Article

Hyperthermia and Body Energy Store Effects on Estrous Behavior, Conception Rate, and Corpus Luteum Function in Dairy Cows

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Abstract

The reproductive performance of 74 Israeli Holstein dairy cows was examined during summer. Cows were fed prepartum to reach high (3.8) and low (2.6) body condition scores by 1 mo prepartum. After calving, half of each group were cooled seven times a day for 30 min by sprinkling and ventilation. Cows were inseminated starting 60 d postpartum. Daily mean body temperatures of cooled and noncooled cows were 38.6 and 39.2 degrees C, respectively, with differences between them reaching 1 degree C and more during the hot hours. Body condition affected only the time taken postpartum to the start of ovarian activity (26 d for high and 32 d for low body condition groups). Estrous behavior lasted longer in cooled (16 h) than in noncooled (11.5 h) cows of the low body condition group only. Conception rate was higher in cooled than in noncooled cows (59 vs. 17%). Pregnancy rate at 90 d postpartum was higher in cooled (44%) than in noncooled cows (14%). Progesterone concentrations were higher in inseminated nonpregnant and in noninseminated cyclic cooled cows than in noncooled cows and were similar in pregnant cows of both cooled and non-cooled groups. The present cooling method appears to have a high potential for improvement of summer fertility.

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... It has been shown that corrective management decisions to compensate for the current environment has as influence on conception rate. Wolfenson et al. (1988) used four fans and a sprinkler system along with timed forced ventilation as the cooling system to analyze the differences between cooled and noncooled females. Cooled cows had higher first service conception rates compared to the non-cooled females, 59% to 17%, respectively (Wolfenson et al., 1988). ...
... Wolfenson et al. (1988) used four fans and a sprinkler system along with timed forced ventilation as the cooling system to analyze the differences between cooled and noncooled females. Cooled cows had higher first service conception rates compared to the non-cooled females, 59% to 17%, respectively (Wolfenson et al., 1988). The same pattern was recognized (P < 0.01) when all inseminations were used to compare cooled cows to non-cooled cows with rates of 57% versus 20%, respectively (Wolfenson et al., 1988 heifers to examine the effects of cold stress, no stress, and heat stress. ...
... Cooled cows had higher first service conception rates compared to the non-cooled females, 59% to 17%, respectively (Wolfenson et al., 1988). The same pattern was recognized (P < 0.01) when all inseminations were used to compare cooled cows to non-cooled cows with rates of 57% versus 20%, respectively (Wolfenson et al., 1988 heifers to examine the effects of cold stress, no stress, and heat stress. Heifers exposed to cold stress were approximately 16% less likely to become pregnant compared to heifers that received no stress, while heat stress showed minimal effects (Chebel et al., 2007). ...
... Like in other mammals, heat stress can compromise physiology and health of dairy cows. Among the most economically important consequences of heat stress are depressed milk yield (Rhoads et al. 2009), low fertility (Wolfenson et al. 1988), and compromised fetal development (Tao et al. 2019). Kekana et al. (2018) and Kino et al. (2019) provide recent example of how heat stress can compromise milk yield and reproduction. ...
... An even greater positive impact of tunnel-ventilation barns than 40% would be expected if differences in seasonal patterns of milk yield were compared for purpose-built tunnelventilation barns such as those studied here for north Florida. Moreover, heat stress can also affect reproduction (Wolfenson et al. 1988) and it is expected that tunnel ventilation would also reduce infertility caused by heat stress. ...
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Tunnel ventilation is an increasingly popular approach to mitigate the effects of heat stress on dairy cattle. Tunnel-ventilation barns use a bank of high-power fans to move air horizontally from one end of the barn to the other at cow level. The overall objective of the present experiments was to determine whether tunnel ventilation is superior to housing with fans and sprinklers with respect to rectal temperature during heat stress and seasonal variation in milk yield. In the first study, rectal temperatures were measured for 1097 lactating Holstein cows in six freestall barns with fans and sprinklers and 575 lactating Holsteins in four tunnel-ventilated freestall barns at a time point between 14:00 and 16:00 h during the months of June to August in Florida, USA. Rectal temperatures were lower for cows in tunnel-ventilation barns than sprinkler-and-fan barns when the tunnel-ventilation barns were built de novo but not when the tunnel-ventilation barns were produced by retrofitting a sprinkler-and-fan barn (interaction, P = 0.0129). In the second study, average daily milk yield in the first 90 days in milk was examined for 8470 lactating Holsteins housed in three sprinkler-and-fan barns and two tunnel-ventilation barns. Milk production for cows calving in cool weather (October to March) was greater (P < 0.0001) than for cows calving in hot weather (April to September). The seasonal reduction in milk yield was less for cows (P = 0.037) in tunnel-ventilation barns (3.5% decrease) than for cows in sprinkler-and-fan barns (5.8% decrease). With this difference in impact of heat stress, it was estimated at a dairy farm could invest up to a $332 more per cow space in a tunnel-ventilated barn than in a sprinkler-and-fan barn. It was concluded that housing cows in tunnel-ventilation barns can reduce the impact of heat stress on body temperature regulation and milk yield.
... Cows kept permanently under HS initially have plasma P 4 concentrations similar to those in a thermoneutral (TN) environment, although there are lower P 4 concentrations between the 6 and 14 days after estrus ( Howell et al., 1994;Wolfenson et al., 1988a;Alhussien et al., 2018), probably due to HS effects on luteal development. However, when HS occurs after ovulation, plasma P 4 concentrations are similar in HS and TN cows (Wilson et al., 1998b;Mogollón et al., 2020), implying that post-ovulation HS does not affect luteal steroidogenesis or P 4 metabolism. ...
... In two studies, HS increased luteal phase ~9 and ~2 days in cows and heifers, respectively (Wilson et al., 1998a,b), implying delayed luteolysis. However, this was not confirmed in another study (Trout et al., 1998), and in yet another, there were indications of premature luteolysis (Wolfenson et al., 1988a). Lastly, in a study by our group, HS did not affect luteolytic responses in non-lactating Holstein cows given 5 or 12.5 mg of PGF2α, implying that HS did not alter PGF2α luteal sensitivity (Mogollón et al., 2020). ...
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Heat stress (HS), a harmful condition affecting animal production, reproduction, and welfare, occurs when an animal is exposed to temperatures that exceed its thermal comfort zone. Several nonspecific body responses involving neural, neuroendocrine, and immune systems are triggered to keep homeostasis in such conditions. These responses, primarily directed to cooling the body, also impact the hypothalamic-pituitary-gonadal axis, compromising the bovine female’s release of gonadotropins. Heat stress also promotes reactive oxygen species accumulation in ovarian cells, impairing protein folding and refolding, triggering antioxidant and DNA protection mechanisms. These mechanisms, directed to reduce cell metabolism and increase survival chances, are not always sufficient to protect the cell and result in apoptosis. Heat stress’s systemic and cellular consequences impact ovarian estradiol production, estrous behaviors, follicular development, oocytes and embryo competence, conception rates, pregnancy establishment and maintenance, and even the future reproductive efficiency of the progenies of cows exposed to HS during pregnancy. The combat of heat stress includes strategies to alleviate the effect of progressive global warming, management strategies to cool the animals, reduced metabolic heat, and methane production dietary approaches. The use of reproductive biotechs and genetic strategies to increase thermotolerant animals are also critical to overcoming the harmful effect of HS.
... It is well accepted that intensive selection for increased milk yield is associated with a decline in reproductive performance of dairy cows [1]. In addition, accumulating evidence indicates that reproductive competence of lactating cows is drastically affected by climate and health [2][3][4]. Taken together, improving fertility has become a major goal of the dairy industry because it will significantly increase the sustainability and efficiency of dairy farms. Therefore, an understanding of the mechanism that underlies the reduction in fertility is required to develop new approaches to cope with the problem. ...
... In light of global warming, it seems that the reduced fertility of lactating cows during the summer will worsen in the coming years. The most common strategy to alleviate the effect of HS is to provide shade and evaporative cooling, based on combining sprinkling and ventilation in both the holding pen and the feeding area [2,4]. However, although intensive cooling mostly prevents the decline in milk production, this approach barely improves conception rate and fertility remains relatively low during the summer [4]. ...
... In heat stressed cows, the duration and intensity of estrus were reduced (Gangwar et al., 1965;Gwazdauskas et al., 1981;Younas et al., 1993;Rodtian et al., 1996) and the incidence of anestrus and silent ovulation were increased (Gwazdauskas et al., 1981). Wolfenson et al. (1988) reported that during the summer months in Israel, estrus behavior lasted longer (16 h) for cooled than in non-cooled Holstein cows with low BCS. The reduction in the number of mounts in hot weather compared to cool weather was observed (Pennington et al., 1985). ...
... In a study by Roth et al. (2000), plasma progesterone concentrations during the estrus cycle in cows that were exposed to heat stress or were cooled did not differ between groups and during the subsequent cycle and, plasma progesterone concentrations did not differ between previously heat stressed or cooled cows. Wolfenson et al. (1988) and Wise et al. (1988 b ) found in earlier studies that plasma progesterone concentrations were decreased in heat stressed cows. Rosenberg et al. (1982) found that plasma progesterone concentrations measured during the estrus cycle before the first insemination was higher in the winter than in the summer in multiparous, but not in primiparous cows. ...
Article
EXP.1 The objectives were to analyses the potential impact of heat stress in different regions, determine the monthly distribution of calving throughout the year and to investigate environmental sources of variation of days open (DO) in first lactation cows. The climate data were obtained from from the 25 official provincial meteorological stations covering the 33 provinces included in the study. Reproductive data were obtained from the bureau of Biotechnology in Livestock Production, Department of Livestock Development, Ministry of Agriculture and Cooperatives. These data contained information from 13,548 lactation records collected from years 2004 to 2006. The lower mean temperature-humidity index was observed in December (72) and the highest mean in April (80). THI differed significantly between regions (P<0.0001), and months (P<0.0001). Significant interactions between region and month (P<0.0001) was found on THI. THI values were different among regions (P<0.0001). The highest frequencies of calving were observed in September and October (13.1 - 14.91%) and the lowest frequencies were observed in February (4.14 - 5.12%). The average DO in the first lactation cows was 151.70 days. Significant effects of MOC (P<0.0001), region (P<0.0001) were found on DO. February calving cows had longest DO (219 ± 11 days) while cows calving in October and November had a significantly shorter mean DO (133 ± 7 and 133 ± 7 days). EXP. 2 The aims of this study were 1) to investigate the effect of heat stress on the resumption of ovarian activity and plasma non-esterified fatty acids (NEFA), insulin-like growth factor-1 (IGF-1) and cortisol concentrations in post partum first lactation dairy cows, and 2) to investigate the effect of heat stress on embryonic loss in first lactation dairy cows. This study was conducted in a commercial dairy farm. There were 68 first lactation cows included in the study. The proportion of normal ovarian cyclicity in mild stress (72 ≤ THI < 78) was higher than in severe stress (78 ≤ THI < 89) group (P<0.01). The interval from calving to first ovulation, interval from calving to first AI, days open and first service conception rate were not statistically different between MS and SS. BCS and body weight were unaffected by THI classification group. Plasma concentrations of NEFA, IGF-1 and cortisol, were not different between groups. Milk production was different (P=0.03) between MS and SS. Neither the number nor the different types of embryonic mortality were affected by heat stress. EXP. 3 The objective was to investigate whether a supplement of beta-carotene given during the dry period is able to 1) increase blood concentrations of beta-carotene postpartum 2) improve ovarian function and progesterone production 3) enhance uterine involution and uterine health 4) improve milk production and milk composition 5) modify hormone and metabolic status in cow 6) increase colostral IgG content 7) modify hormone, metabolic status and enzyme activity in the neonatal calf. Forty high producing Holstein cows were included in the experiment. The beta-carotene supplement was given individually to the cows (1g/d beta-carotene) started at drying-off until calving. The results showed that supplementation of beta-carotne during the dry period increased blood concentrations of beta-carotene in cows (P<0.0001). On day 28 postpartum the percentage of neutrophils in the BC group was lower than in the C group (cervical smear; C: 21.0 ± 3.22% vs BC: 9.7 ± 3.14%, P<0.05 and uterine smear; C: 32.0 ± 3.86% vs BC: 20.9 ± 3.76%, P<0.05). Plasma concentrations of hydroxyproline in the BC group were higher than in the C group on day 21 postpartum (BC: 20.8 ± 1.33µmol/L vs. C: 15.0 ± 1.33µmol/L; P<0.01). The dietary supplement of beta-carotene during the dry period had no effect on ovarian activity, progesterone production, cervix and uterine horn diameters, milk production and milk composition, hormone and metabolic status in cow, colostral IgG content, hormone, metabolic status and enzyme activity in the neonatal calf.
... For example, poor luteal activity has been associated with the intense metabolism and steroid hormone clearance of high milk production [33,34]. Heat stress is also a main factor impairing the CL function [35][36][37]. Luteal deficiency, therefore, is not due to a single etiology, and an etiologic diagnosis may be difficult or impossible to establish in routine clinical practice. Irrespective of its origin, the diagnosis of sub-luteal function can be performed clinically on the basis of plasma or milk P4 concentrations. ...
Article
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Luteal deficiency is defined as reduced progesterone (P4) steroidogenesis by the corpus luteum (CL), either in the amount or duration, or both. This work provides a clinical overview of the current understanding of luteal deficiency and its association with low fertility in dairy cows. Low plasma P4 concentrations during the luteal phase post-artificial insemination (AI) are associated with lower conception rates. Treatments post-AI with P4, gonadotropin-releasing hormone (GnRH) or human chorionic gonadotropin (hCG) improve fertility in some conditions. Sub-luteal function during the late embryonic period (at pregnancy diagnosis, i.e., 28–34 days post-AI), is just one factor among other factors associated with pregnancy loss. Treatment with P4 in cows with one CL favors pregnancy maintenance, while GnRH treatment does the same in cows carrying twins. The diagnosis of sub-luteal function can be made clinically on the basis of plasma or milk P4 concentrations. Automated in-line milk P4 analysis systems to diagnose luteal activity emerge as a very interesting tool in dairy herds. Monitoring plasma or milk P4 concentrations with the help of Doppler ultrasonography to assess the CL function would allow individualizing the luteal phase support.
... Diese äußeren sich u.a. durch einen Anstieg der Anöstrusraten (Polsky and von Keyserlingk, 2017; Hansen, 2020), reduzierte Konzeptionsraten (Wolfenson et al., 1988;Kadzere et al., 2002, Schüler et al., 2016, reduzierte Embryonalentwicklungsraten (Kasimanickam and Kasimanickam, 2021) oder erhöhte Embryonalmortalitäten und Abortraten. Die ersten sieben Tage der Embryonalentwicklung sind dabei besonders anfällig für eine Störung durch Hitzestress (Hansen, 2019). ...
Article
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Due to global warming, the thermal stress of farm animals in form of heat stress will increase in importance even in the temperate climate zones of Central Europe. High-yielding animals in open barn husbandry systems, i.e., especially dairy cows, are particularly affected by this. However, studies also show that there can be significant effects in animals kept in closed systems, i.e., under relatively controlled environmental conditions. These include high-yielding breeding sows, which, like cows, already experience excessive thermal stress due to their increased metabolic performance. To estimate the consequences of thermal stress, scientific studies commonly use temperature-humidity indices (THI), a combination of temperature and relative humidity (RH). Based on these indices, many studies highlight that heat stress affects performance, feed intake, and animal health, reproduction and welfare in both dairy cows and pigs. This literature review describes the effects of heat stress on the technological characteristics and qualities of milk from dairy cows, as well as fertility, health and welfare in dairy cows and breeding sows. In order to counteract the problem of heat stress, there are several possibilities to make suitable adjustments at different levels of animal production. These include feeding (e.g. fodder production), husbandry (e.g. air-conditioned housing) and animal management (e.g. fertility management, breeding).
... Studies comparing blood estradiol concentrations in heat stressed cow and control cows gave inconsistent results [119,120,123e125] but there is a considerable body of evidence showing that heat stress reduced the steroidogenic capacity of theca and granulosa cells in vitro leading to diminished blood estradiol concentrations [43,44,64,65,68,69,119,121,122,126e128]. Decreased plasma concentration of estradiol compromised follicular development, modified ovulatory mechanisms and reduced the quality of oocytes and embryos [43,44,67,119,121,122,126,127]. ...
Article
In the Northern Hemisphere, from June to September and in the Southern Hemisphere from December to March, there are periods of reduced fertility (sub-fertility) in dairy cows that are described as summer infertility. Several factors contribute to sub-fertility during this time, such as ambient temperature, humidity and photoperiod. During the warm season there is a reduction in feed intake that may compromise the energy balance of the cow and/or induce an imbalance in the activity of the hypothalamo-hypophyseal-ovarian axis. These factors reduce the reproductive performance of the cow and compromise the quality of oocytes, embryos and corpora lutea. This paper reviews current knowledge on the metabolic and endocrine mechanisms that induce summer infertility and describe their effects on follicle, oocyte and embryo development in dairy cows.
... Among the potentially adverse effects of heat stress associated with low estradiol levels are 1) reduced plasma estradiol concentration (Badinga et al., 1993;Wolfenson et al., 1995) impairing estrus dura-tion and intensity, increasing incidence of anestrus and silent ovulation, and reducing number of mounts (Gwazdauskas et al., 1981;Wolfenson et al., 1988); 2) suppression of pulsatile LH release and the preovulatory LH surge (Wise et al., 1988;Gilad et al., 1993) which, in turn, might impair events associated with ovulation, oocyte maturation, or both; 3) development of nonovulatory follicles or formation of ovarian cysts; and 4) alteration in luteal functioning, that is, reduced progesterone production and secretion . ...
... This reduction may be associated with endocrine changes and the follicular microenvironment where the oocytes are exposed, leading to a lower development competence, which denotes the complexity of these mechanisms (ROTH, 2012). As an alternative, to solve the negative effects of high temperatures on reproductive performance, cooling methods should be used, such as sprinkling and ventilation, which can reduce RT of Holstein cows and, thus, improve CR (WOLFENSON et al., 1988). ...
Article
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This study aimed to evaluate the effects of rectal temperature (RT) on conception rate (CR), as well as the effects of seasonality (spring-summer vs. autumn-winter) and timing of artificial insemination (AI) (morning vs. afternoon) on RT and CR in crossbred dairy cows (Holstein x Gyr). The experiment was conducted on a dairy farm in Centralina, MG, where 1,219 conventional and fixed-time inseminations were analyzed. The RT was measured immediately before AI using a digital thermometer. Pregnancy diagnosis was performed using ultrasonography between 28 and 60 days after AI. T The effects of seasonality and timing of AI on RT were analyzed with a Mann-Whitney U test and the effects of RT (above or below the average), seasonality and timing of AI on CR were analyzed with a Chi-squared test, both using the SAS program. The RT average was 39.4°C. Cows with RT ? 39.4°C had lower CR than cows with RT < 39.4°C (25.78% vs. 32.54%; P = 0.0096). During spring-summer, cows had higher RT (39.44°C ± 0.025 vs. 39.27°C ± 0.022; P < 0.0001) and lower CR (25.49% vs. 31.75%; P = 0.0146) compared with autumn-winter. Cows inseminated in the morning had lower RT (38.96°C ± 0.022 vs. 39.60°C ± 0.018; P < 0.0001) and higher CR (32.86% vs. 26.06%; P = 0.0102) than cows inseminated in the afternoon. In conclusion, crossbred dairy cows with rectal temperature equal to or greater than 39.4°C had lower conception rate. Moreover, rectal temperature and conception rate were affected by seasonality and insemination time.
... In spite of the measures undertaken during the summer months to ameliorate the adverse effects of heat load in the present study, absence of contemporary controls and the impossibility to quantify the adequacy of the cooling system prohibited critical evaluation of the efficiency of these measures. Nevertheless, intense and frequent use of sprinkling and ventilation cooling under experimental farm conditions (Flamenbaum et al. 1986) seemed able to restore the summer conception rate to that noticed in the winter (Wolfenson et al. 1988). Nevertheless, management interventions to ameliorate the effects of heat load on conception rate should be implemented at least 5 weeks before anticipated service and should continue until at least 1 week after service (Morton et al. 2007). ...
... Furthermore, to meet the requirements of the study design, animals were maintained insecticide free until the designated treatment administration day for each herd and their respective experimental trial. Suggestions of developing a tolerance to environmental stressors have been made (Wolfenson et al. 1988, du Preez et al. 1990. It is possible that animal maintenance in preparation for the study initiation allowed these animals to develop a tolerance to horn fly infestation and their associated stresses. ...
Article
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The behavioral responses of cattle under the influence of naturally occurring seasonal horn fly, Haematobia irritans (L.), populations were evaluated under rangeland conditions. This study was replicated four times using 10 cows as the subsampling unit equipped with GPS collars scheduled to receive locational fixes every 5 min for 6 d prior to, and 6 d following horn fly insecticidal control application. Data derived from GPS collars were used to evaluate potential horn fly-induced behavioral modifications expressed during predawn, daytime, and nighttime periods. These data were used to analyze variables, which included distance travelled, daily area explored, vertical and horizontal head movements, and inferred activities such as resting, grazing, and walking. Horn fly populations were estimated using daily visual counts and were reduced significantly on animals following insecticidal application. There was no significant difference between treatment periods in any of the aforementioned analyzed variables. During the night-time hours estimated differences (pretreatment minus posttreatment) for distance travelled, area explored, and vertical head movements were 0.81 ± 0.46 km/d, 0.35 ± 0.21 km(2)/d, and 7.25 ± 5.30 counts/d, respectively. The implications of these observations are discussed.
... En el periodo 2 los resultados fueron similares a los del periodo 1, ya que el tratamiento T 3 solo redujo en 0,37 y 0,38ºC la temperatura rectal con respecto a T 1 y T 2 (p<0,01). Diferencias superiores fueron reportadas por Her et al. (1988) con medias de 0,5 a 0,9ºC entre vacas con enfriamiento y sin enfriamiento, resultados similares también fueron reportados por Wolfenson et al. (1988). ...
Article
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The objective of this study was to evaluate the effect of a timed artificial insemination protocol plus a period of artificial cooling on conception rate and physiologic response of heifers under heat stress. Ninety Holstein heifers were randomly allotted into one of three treatments: A control treatment (T1) with visual heat detection and insemination morning-evening (n=30), a second treatment (T2) under a timed artificial insemination protocol and a third treatment (T3) with the same protocol than T2 plus an artificial cooling period beginning 11 d before and ending 21 d after insemination. The experiment was divided in two periods: the first period was from June 25 to July 26, and the second one from August 15 to September 16. In period 1, heifers in T3 had a lower (p<0.01) rectal temperature (39.35°C) compared to T1 (39.68°C) and T2 (39.67°C); respiration rate (breaths/min) was more reduced (p<0.01) in T3 (72) in comparison to T1 (85) and T2 (84). Conception rate was not different between T3 (64.3%) and T1 (46.7%) but both showed a tendency to be different (p<0.10) to T2 (13.3%). During the period 2, the rectal temperature in T3 (39.24°C) was lower (p<0,01) than T1 (39.61°C) and T2 (39.62°C). Respiration rate also was decreased (p<0,01) in T3 (77) with respect to T1 (87) and T2 (94), being T1 and T2 different (p<0.01). Conception rate was similar between T3 (40%), T1 (13%) and T2 (13%). The pregnancy rate including both periods had a tendency to be increased (p<0,10) in T3 (51.7%) compared to T2 (13.3%) and T1 (30.0%). The artificial insemination to fixed time plus artificial cooling may be an alternative to increase the fertility of Holstein heifers during the summer.
... La majorité des études réalisées dans des conditions thermiques et hygrométriques particulières telles que celles rencontrées dans des climats tropicaux ou subtropicaux reconnaissent une diminution de la fertilité au cours des mois d'été, surtout si la température extérieure le jour ou le lendemain de l'insémination est élevée (>27-30°C) (Ingraham et al. 1974, Gwasdauskas et al. 1981a, Francos et Mayer 1983, Stevenson et al. 1983a, Ron et al. 1984, Badinga et al. 1985, Cavestany et al. 1985b, Wolfenson et al. 1988, Du Preez et al. 1991, Silva et al. 1992, Weller et Ron 1992, les vaches hautes productrices étant plus sensibles que les autres (Thatcher et Collier in Badinga et al. 1985) ou que les génisses . L'augmentation de la température entraînerait une diminution de la viabilité et du développement des embryons âgés de 6 à 8 jours (Monty et Racowsky 1987). ...
Thesis
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Notre travail poursuivait deux objectifs essentiels: mettre au point d'une part un système de collecte et d'analyse d'observations compatible avec l'activité journalière du praticien et, à partir de la banque de données ainsi constituée procéder d'autre part à une étude comparée chez la vache laitière et viandeuse, de l'influence des facteurs individuels et d'environnement sur les pathologies puerpérales et du post-partum ainsi que sur la fertilité et la fécondité. La première partie de notre travail (Chapitre 1: Introduction générale) a été dévolue à une analyse exhaustive au travers des données de la littérature des facteurs responsables des problèmes de reproduction. Ils peuvent se répartir en deux catégories: les facteurs individuels d'une part et les facteurs collectifs d'autres part. Au nombre des premiers il faut citer l'âge, la génétique, le niveau de production laitière, le type de vêlage, la gémellité, la mortalité périnatale, la rétention placentaire, la fièvre vitulaire, l'involution cervicale et utérine, les infectioins du tractus génital et l'activité ovarienne au cours du postpartum. A l'inverse les facteurs collectifs font davantage référence au troupeau qu'à l'individu. Ils concernent le choix d'une politique de première insémination, la détection des chaleurs, le moment de l'insémination, la nutrition, la saison, le type de stabulation, la taille des troupeaux et les caractéristiques sociologiques de l'éleveur. Cette revue de la littérature nous a permis de constater la grande diversité des effets observés à l'encontre des facteurs étudiés d'une part et le manque habituel d'harmonisation concernant les méthodes d'évaluation de ces effets. Deux chapitres de notre travail ont été consacrés à la présentation du logiciel de gestion de la reproduction GARBO. Celui-ci comprend deux aspects différents au demeurant complémentaires. Le premier plus propédeutique est basé sur le suivi mensuel de reproduction (Chapitre 2). Le second plus analytique comporte l'analyse mensuelle mais surtout annuelle des performances et pathologies de la reproduction (Chapitre 3). Au travers de différentes listes d'intervention, le programme assure le suivi sanitaire et zootechnique de chaque individu femelle depuis l'âge de 14 mois ou depuis son dernier vêlage jusqu'à la confirmation de la gestation ou de la réforme. Il contribue ce faisant à réduire les périodes de non reproduction. Parce qu'il fournit au vétérinaire une anamnèse physiologique, pathologique et thérapeutique, il lui permet d'affiner son diagnostic et de prendre en connaissance de cause une décision thérapeutique appropriée. Le programme a déjà fait l'objet de nombreuses améliorations, fruit de son expérimentation sur le terrain. Puisqu'il ne peut y avoir de gestion sans quantification, l'évaluation des performances de reproduction représente le second aspect au demeurant essentiel d'une démarche préventive de la reproduction. D'une manière générale, nous avons cherché à optimiser et à actualiser au maximum les données disponibles au sein de chaque troupeau. La mise au point d'un bilan de reproduction a été illustrée par la comparaison des performances enregistrées en 1992 dans 3 systèmes d'élevage, le premier ne comportant que des animaux viandeux allaitants de race Blanc Bleu Belge (n = 20). le second (n = 45) que des animaux laitiers de race Holstein Frisonne ou Pie Rouge et le troisième (n = 39) qualifié de mixte rassemblant des animaux viandeux traits ou allaitants de race Blanc Bleu Belge et des animaux de race laitière. Cette étude comparative est la première du genre et peut servir de référence au clinicien pour l'interprétation des performances de troupeau de sa clientèle. Cette étude comparée nous a permis d'identifier plusieurs faits. Quelle que soit la spéculation, les exploitations présentent de larges différences dans les performances moyennes de reproduction. Cette observation traduit vraisemblablement davantage les capacités différentes des éleveurs à gérer leur potentiel de reproduction que les différences liées à la race ou au type de production laitière ou viandeuse. Elle se trouve confirmée par le fait qu'au sein de chaque spéculation, certains troupeaux atteignent pour les différents paramètres étudiés, les valeurs considérées comme optimales. La fécondité des génisses exprimé par l'âge du premier vêlage est comparable quel que soit le type de spéculation allaitante (28 mois), mixte (29 mois) ou laitière (29 mois). Moyennant le respect de certains conditions sanitaires et nutritionnelles, il apparaît que la race viandeuse Blanc Bleu Belge est aussi précoce que les races laitières. La fécondité des vaches exprimée par le délai nécessaire à l'obtention d'une gestation est meilleure dans les troupeaux laitiers (111 jours) qu'allaitants (125 jours), les troupeaux mixtes présentant une situation intermédiaire (117 jours). Ce fait résulte essentiellement d'une première insémination plus tardive dans les troupeaux allaitants (84 jours) que mixtes (76 jours) ou laitiers (73 jours), suite à une période d'anoestrus plus prolongée identifiée indirectement par l'intervalle entre le vêlage et la première chaleur détectée par l'éleveur et respectivement égale en moyenne à 79, 67 et 59 jours dans les troupeaux allaitants, mixtes et laitiers. En effet, les trois spéculations présentent une fertilité comparable qu'elle soit exprimée par le pourcentage de gestation en première insémination (45 %) ou par le nombre d'inséminations nécessaires à l'obtention d'une gestation (troupeaux allaitants: 2.4, mixtes: 2.5 et laitiers: 2.3). La qualité de la détection des chaleurs caractérise les trois types de spéculation. Enfin, les troupeaux laitiers présentent une fréquence plus élevée de pathologies puerpérales (rétention placentaire et fièvre vitulaire) et du post-partum (métrites, kystes ovariens) que les élevages allaitants ou mixtes). Dans le chapitre 4, nous avons cherché à décrire la fréquence des pathologies puerpérales et du postpartum et à en identifier les facteurs de risque individuels ou d'environnement chez la vache viandeuse et laitière. Ont ainsi été étudiées la rétention placentaire, la fièvre vitulaire, l'involution utérine, les infections utérines et les kystes ovariens. Les valeurs fréquentielles observées (Tableau 59) sont les premières du genre pour les conditions d'élevage que nous connaissons. A ce titre, elles ont valeur de référence. Les pathologies puerpérales telles que la rétention placentaire et la fièvre vitulaire sont plus fréquentes chez la vache laitière que chez la vache viandeuse. La vache laitière se caractérise par ailleurs par une plus grande fréquence de retard d'involution utérine et de kystes ovariens que la vache viandeuse. L'infection du tractus génital constitue la pathologie dominante et sa manifeste avec la même fréquence dans les deux spéculations. D'une manière générale, la proportion de vaches atteintes par une ou plusieurs pathologies est plus élevée dans la spéculation laitière que viandeuse. Une fois quantifiée la fréquence des pathologies dans les deux spéculations, nous avons cherché à en identifier les facteurs de risque par la méthode des Odds Ratio et de la régression logistique. Certains se sont avérés être communs aux deux spéculations pour une pathologie donnée. Ainsi, l'âge de l'animal contribue à augmenter le risque de rétention placentaire et de retard d'involution utérine, la réduction de la longueur de la gestation celui de la rétention placentaire et la césarienne celui de l'infection utérine. De même, la gémellité augmente le risque de rétention placentaire et d'infection du tractus génital alors que la rétention placentaire et le retard d'involution utérine favorisent l'infection du tractus génital dont la présence augmente le risque de retard d'involution utérine. A l'inverse, nous avons constaté un effet plus spécifique de certains facteurs en fonction de la spéculation surtout en ce qui concerne la rétention placentaire et la fièvre vitulaire chez la vache laitière ce qui laisse en présumer une pathogénie commune. La saison du vêlage influence davantage le risque d'une pathologie chez la vache laitière que chez la vache viandeuse. Ce fait reflète peut-être l'effet indirect de la production laitière à l'origine d'un métabolisme différent. Sur le plan pratique, il est intéressant de distinguer deux types de facteurs. Les uns sont davantage inhérents à l'animal. Ils sont par conséquent moins directement modifiables . Qualifiés de "marqueurs de risque", ils concernent le numéro de lactation, la longueur de la gestation, le nombre de veaux et la saison du vêlage. D'autres peuvent davantage être considérés comme des "facteurs de risque "proprement dit dans la mesure ou ils peuvent faire l'objet d'une attitude préventive ou curative de la part du vétérinaire. Ainsi chez la vache viandeuse le recours à la césarienne sera préféré au vêlage réalisé par traction pour diminuer la fréquence du retard d'involution utérine. Un suivi thérapeutique anti-infectieux de cette intervention chirurgicale ainsi que de la rétention placentaire sera de nature à diminuer la fréquence des infections du tractus génital et à favoriser la qualité de l'involution utérine. Chez la vache laitière, la prévention de la fièvre vitulaire et une meilleure détection du vêlage contribueront à réduire l'incidence de la rétention placentaire directement ou indirectement par la diminution de la mortalité néonatale. Ce faisant, le risque d'infection utérine sera réduit et ainsi la fréquence du retard d'involution utérine s'en trouvera diminué ce qui contribuera à réduire le risque de kystes ovariens. Le chapitre 5 a été consacré à l'étude comparée chez la vache laitière et viandeuse de la fertilité et de la fécondité ainsi que de leurs facteurs de risque individuels ou d'environnement. La fertilité et la fécondité ont été analysées respectivement par le pourcentage de gestation en première insémination et par l'intervalle entre le vêlage et l'insémination fécondante. Les pathologies puerpérales et du post-partum étudiées exercent d'une manière générale peu d'effet direct sur ces deux paramètres. En effet, chez la vache laitière, le pourcentage de gestation en première insémination ne se trouve diminué que par la rétention placentaire et par la présence d'une infection du tractus génital 41 à 50 jours après le vêlage tandis que la fièvre vitulaire est la seule pathologie à avoir une influence négative sur l'intervalle entre le vêlage et l'insémination fécondante. Il faut sans doute voir dans cette constatation l'effet positif exercé indirectement par la mise en place d'un suivi mensuel de reproduction. Celui-ci offre en effet au praticien la possibilité d'un dépistage et par conséquent d'un traitement précoce des pathologies rencontrées. Par ailleurs, il est possible que ces pathologies contribuent davantage à augmenter le risque de réforme de l'animal que celui d'infertilité ou d'infécondité. Au vu de notre étude, l'amélioration du pourcentage de gestation en première insémination constitue une priorité essentielle chez la vache laitière mais plus encore chez la vache viandeuse. Elle peut être espérée chez la première en évitant le recours à la césarienne, en prévenant la rétention placentaire qui prédispose aux infections du tractus génital, en évitant d'inséminer l'animal avant le 50ème jour du post-partum et en agissant sur les facteurs susceptibles de réduire l'anoestrus du postpartum Chez la vache viandeuse de race Blanc Bleu belge, la césarienne constitue un "mal nécessaire". La réduction de la fertilité qu'elle entraîne est le prix à payer mais non un obstacle à la politique de sélection viandeuse de plus en plus intensive menée dans cette spéculation. Le recours à des conditions optimales pour sa réalisation qu'elles soient de nature chirurgicales ou hygiéniques doit permettre de réduire les complications péritonéales et par conséquent à améliorer le pourcentage de gestation en première insémination. Nos résultats nous incitent par ailleurs à postposer après le 70ème jour du post-partum le moment de la première insémination chez la vache viandeuse et à ne pas recommander l'utilisation de spirales vaginales pour l'induction de la première chaleur après le vêlage. Sans doute, il serait intéressant d'étudier l'impact de solutions alternatives telles que la politique d'un sevrage précoce sur la réapparition rapide d'une activité ovarienne après le vêlage, facteur pouvant contribuer à réduire l'utilisation de traitements inducteurs. L'influence des variables antérieures est pratiquement nulle dans les deux spéculations à l'exception toutefois de la fièvre vitulaire chez la vache laitière. Cette observation devrait inciter le praticien a tenir compte du passé métabolique de l'animal pour décider du traitement préventif des animaux à risque.
... Among the potentially adverse effects of heat stress associated with low estradiol levels are 1) reduced plasma estradiol concentration (Badinga et al., 1993;Wolfenson et al., 1995) impairing estrus dura-tion and intensity, increasing incidence of anestrus and silent ovulation, and reducing number of mounts (Gwazdauskas et al., 1981;Wolfenson et al., 1988); 2) suppression of pulsatile LH release and the preovulatory LH surge (Wise et al., 1988;Gilad et al., 1993) which, in turn, might impair events associated with ovulation, oocyte maturation, or both; 3) development of nonovulatory follicles or formation of ovarian cysts; and 4) alteration in luteal functioning, that is, reduced progesterone production and secretion . ...
Article
In light of the intensive genetic selection for high milk production and the onset of global warming, it seems that the reduced fertility of lactating cows during the summer will worsen in coming years. Although not entirely clear, the mechanism appears to be multifactorial in nature. It includes alterations in follicular development, depression of follicular dominance, and impairment of steroidogenesis and gonadotropin secretion. Heat-induced perturbations in the physiology of the follicle-enclosed oocyte have also been documented, expressed by impaired cleavage rate and reduced developmental competence. With respect to the oocyte, alterations include an increase in PUFA in the membrane, reactive oxygen species, ceramide formation and caspase activity, and induction of apoptosis via the sphingomyelin and/or mitochondrial pathways. New insight into cellular and molecular alterations has revealed that heat induces perturbations in both nuclear and cytoplasmic maturation events, such as resumption of meiosis, metaphase II plate formation, cytoskeleton rearrangement, and translocation of cortical granules. Alterations in mitochondrial distribution (i.e., low proportion of category I mitochondria) and function (i.e., low membrane potential) have recently been reported for oocytes collected during the summer. These were associated with impaired expression of both nuclear (succinate dehydrogenase subunit [SDHD], adenosine triphosphate [ATP] synthase subunit beta [ATP5B]), mitochondrially NADH dehydrogenase subunit 2 (), and mitochondiral (cytochrome c oxidase subunit II [MT-CO2] and cytochrome b [MT-CYB]) genes that are crucial in the mitochondrial respiratory chain. In addition, season-induced alteration in the stored maternal mRNA has been documented, expressed by reduced transcript levels (oocyte maturation factor MOS [], growth differentiation factor 9 [], POU domain class 5 transcription factor 1 [], and glyceraldehyde-3-phosphate dehydrogenase []) in metaphase II stage oocytes and embryos before (i.e., 2-, 4-, and 8-cell stages) and after (i.e., 8- to 16-cell stage) embryonic genome activation. Taken together, the findings indicate an association between cellular and molecular modifications and reduced developmental competence during the hot seasons. Such knowledge is essential for the development of new approaches to cope with this unsolved problem.
... Reproductive success is dependent upon appropriate circulating concentrations of hormones such as progesterone, as it is critical to reproductive events ranging from follicular development to the maintenance of pregnancy (Wiltbank et al., 2011). Whereas many have shown that HS affects circulating progesterone concentrations in cattle, results have been highly variable (Abilay et al., 1975;Roman-Ponce et al., 1981;Rosenberg et al., 1982;Wolfenson et al., 1988). These apparent discrepancies are likely due to study-specific variation in the factors that determine circulating concentrations, including progesterone production (luteal and possibly adrenal), hepatic blood flow or metabolism, hemodilution, and hemoconcentration (Trout et al., 1998) Progesterone metabolism by the liver is influenced by many factors, one of which is insulin. ...
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Two experiments were performed to determine the effects of heat stress (HS) and insulin on hepatic mRNA abundance of enzymes responsible for metabolizing progesterone [cytochrome P450 2C and 3A (CYP2C and CYP3A)]. To distinguish the direct effects of HS from decreased dry matter intake, cohorts were pair fed (PF) in thermoneutral conditions to match the intake of the HS cows during both experiments. In the first experiment, multiparous late-lactation Holstein cows (n = 12, 305 ± 33 d in milk) housed in climate-controlled chambers were subjected to 2 experimental periods: (1) thermoneutral (TN) conditions (18°C, 20% humidity) with ad libitum intake (TN and well fed) for 9 d; and (2) either HS conditions (cyclical temperature 31-40°C, 20% humidity) fed for ad libitum intake (n = 6), or TN conditions and PF to match the HS animal (n = 6) for 9 d. To evaluate hepatic gene expression during experiment 1, biopsies were obtained at the end of each period. In the second experiment, multiparous mid-lactation Holstein cows (n = 12, 136 ± 8 DIM) were housed and fed in conditions similar to those described for the first experiment. Liver biopsies were obtained immediately before and after an insulin tolerance test administered on d 6 of each period. No effects of exogenous insulin were observed on any of the tested variables, nor were there interactions between environment (TN/HS or well fed/PF) and insulin administration. Heat stress decreased hepatic CYP2C expression during both experiments. The relative abundance of CYP3A was not affected by environmental conditions in the late-lactation cows (first experiment), but was reduced by HS in the mid-lactation cows (second experiment). Interestingly, during experiment 2, hepatic CYP3A expression also decreased during PF. These results suggest that HS reduces the capacity of the liver to metabolize progesterone through distinct effects on CYP2C and CYP3A, and that the effects appear to vary based upon stage of lactation. Ultimately, HS may affect reproductive outcomes by reducing the abundance of the enzymes responsible for the breakdown of progesterone. This reduction could serve as a beneficial adaptation for rescuing early embryos or may be detrimental, as it affects feedback mechanisms necessary for proper cyclicity. Copyright © 2015 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.
... Earlier results were controversial: some show decreased plasma concentration of progesterone Ž . during HS Wise et al., 1988b;Wolfenson et al., 1988 , others report no change or Ž . increased concentration Thatcher and Collier, 1986;Wise et al., 1988a . ...
... En el periodo 2 los resultados fueron similares a los del periodo 1, ya que el tratamiento T 3 solo redujo en 0,37 y 0,38ºC la temperatura rectal con respecto a T 1 y T 2 (p<0,01). Diferencias superiores fueron reportadas por Her et al. (1988) con medias de 0,5 a 0,9ºC entre vacas con enfriamiento y sin enfriamiento, resultados similares también fueron reportados por Wolfenson et al. (1988). ...
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espanolLas altas temperaturas afectan la reproduccion del ganado bovino reduciendo la intensidad del estro y la fertilidad. Basado en lo anterior el objetivo del estudio fue evaluar los efectos de la inseminacion artificial (IA) a tiempo fijo mas un periodo corto de enfriamiento ambiental sobre la tasa de concepcion y respuesta fisiologica de vaquillas bajo estres calorico. Noventa vaquillas Holstein fueron distribuidas aleatoriamente en uno de los siguientes tratamientos: Un tratamiento testigo (T1) con deteccion visual de estro e IA manana-tarde (n= 30); un segundo tratamiento (T2) bajo un protocolo de IA a tiempo fijo (n= 30) y un tercer tratamiento (T3) con el mismo protocolo de IA de T2 mas un periodo de enfriamiento ambiental (ventilacion y aspersion) de las vaquillas 11 d antes y 21 d despues de la IA (n= 30). El experimento se dividio en dos periodos: el primero del 25 de junio al 26 de julio; el segundo del 15 de agosto al 16 de septiembre. En el primer periodo las vaquillas en T3 tuvieron una temperatura rectal (39,35°C) mas baja (p EnglishThe objective of this study was to evaluate the effect of a timed artificial insemination protocol plus a period of artificial cooling on conception rate and physiologic response of heifers under heat stress. Ninety Holstein heifers were randomly allotted into one of three treatments: A control treatment (T1) with visual heat detection and insemination morning-evening (n= 30), a second treatment (T2) under a timed artificial insemination protocol and a third treatment (T3) with the same protocol than T2 plus an artificial cooling period beginning 11 d before and ending 21 d after inse-mination. The experiment was divided in two pe-riods: the first period was from June 25 to July 26, and the second one from August 15 to September 16. In period 1, heifers in T3 had a lower (p
... Long-term exposure to heat stress may lead to reduced progesterone concentrations, however, because luteal concentrations of the hormone during the luteal phase have been reported to be lower in summer than winter (Howell et al., 1994). Additionally, cooling cows during the summer increased circulating concentrations of progesterone (Wolfenson et al., 1988). Some effects of heat stress on peripheral blood concentrations of hormones could be the result of changes in water balance during heat stress and reduced hematocrit (Richards, 1985;Lamp et al., 2015). ...
... Long-term exposure to heat stress may lead to reduced progesterone concentrations, however, because luteal concentrations of the hormone during the luteal phase have been reported to be lower in summer than winter (Howell et al., 1994). Additionally, cooling cows during the summer increased circulating concentrations of progesterone (Wolfenson et al., 1988). Some effects of heat stress on peripheral blood concentrations of hormones could be the result of changes in water balance during heat stress and reduced hematocrit (Richards, 1985;Lamp et al., 2015). ...
Chapter
Depending on its severity, heat stress can have moderate to severe effects on many aspects of reproductive function in both females and males. Among the most notable effects of heat stress are reduced intensity of behavioral estrus and low fertility in females, and compromised sperm output and increased sperm abnormalities in males. Lactation increases the sensitivity of females to heat stress because the associated increase in heat production makes regulation of body temperature more difficult. Among the strategies to reduce the magnitude of heat stress effects are the provision of housing that contains shade, sprinklers or misters, and fans. Effects of heat stress on estrus detection can be eliminated by the implementation of timed artificial insemination programs. However, such programs do not improve fertility. The most effective means for enhancing pregnancy rate during heat stress is to perform embryo transfer. The embryo transferred at day 7 after estrus has escaped deleterious effects of heat stress and is more resistant to subsequent heat stress than embryos at earlier stages of development. Opportunities also exist for changing cattle genetically to increase their ability for thermoregulation and cellular resistance to elevated temperature.
... In addition to antioxidant therapy, many approaches have been explored to reduce the effects of heat stress experienced by the lactating dairy cow on fertility. Cooling of cows during heat stress increases pregnancy rates (Thatcher et al., 1974;Roman-Ponce et al., 1977;Wolfenson et al., 1988;Ryan et al., 1993;Khongdee et al., 2006) but large seasonal variations in reproductive function can still persist on farms that use such cooling systems (Hansen and Aréchiga, 1999). Reasons for this variation in fertility could be attributed to the delayed effects on follicular development and oocyte competence caused by heat stress, differences in energy balance or milk yield between cows, or inadequate cooling systems. ...
... In this respect, Niekerk et al., (1990), and Freetly and Cundiff (1998) reported that the level of feeding of heifers up to mating at 2 years has little effect on their reproductive performance. In other study with cows, results revealed that body condition was affected only on the time taken postpartum to the start of ovarian activity (26-d for high and 32-d for low body condition group (Wolfenson et al., 1988). Results obtained in Table (7) cleared that CR of the 1 st and 2 nd service were superior for the animals fed R2 than those of other treatments, and all primiparous buffaloes received R1 or R2 were conceived after 2 rd service. ...
... In Israel, this approach was successfully implemented 22 years ago in a large dairy herd. Cooling management based on seven 30-min cooling periods a day enabled maintenance of normal body temperature (< 39.0ºC) in cows producing 30 kg milk/day, and conception rates (CRs) similar to those in the winter (Wolfenson et al. 1988). However today, intensive cooling consisting of 10 periods for a total of 7 cumulative h/day prevents the decline in milk production in extremely high-yielding cows (>13,000 kg/ year) but not that in summer reproduction. ...
... The goal is to maximize the number of wet and dry cycles per hour. Management which based on three cooling periods in the holding pen enables to maintain normal body temperature (<39.0 °C) in cows producing 30 kg milk/d with conception rates similar to those in the winter (Wolfenson et al., 1988). However, for high lactating cows (45 to 50 kg milk/d), intensive cooling consisting of 10 periods for a total of 5 to 7 cumulative h/d are required. ...
... The number and the duration of cooling periods and the interval between periods play a pivotal role in preventing hyperthermia. In Israel, cooling management which based on seven cooling periods a day (30-min each) can maintain normal body temperature in cows producing 30 kg milk/day and to keep the conception rate similar to that in the winter (Wolfenson, Flamenbaum, & Berman, 1988). On the other hand, intensive cooling consisted of 10 cooling periods is required to prevent the decline in milk production in high-yielding cows (>13,000 kg/year; Flamenbaum & Galon, 2010 ...
Article
Reduced reproductive performance of lactating cows during the summer is associated mainly with intensive genetic selection for high milk production, which places a great load on the thermoregulatory mechanism. In the last decades, a big effort has been made to explore the mechanism by which heat stress compromises fertility. The data gained so far revealed that the effect of thermal stress on the female reproductive tract is multifactorial in nature. Based on this understanding, new strategies to mitigate the effect of heat stress have been developed. The review summarizes some of the physiological responses of the cow to elevated temperature and discusses its limitations to maintain normothermia. The review emphasizes that cooling is the predominant strategy used today to alleviate the effects of heat stress. Findings from the Israeli dairy herd indicate that efficient cooling management can improve milk production during the summer to a similar level of the winter, expressed by summer to winter ratio of 0.98. However, cooling as a singular approach cannot eliminate the decline in reproduction. Nonetheless, an efficient cooling system is a prerequisite for any other strategy. The review suggests additional hormonal treatments to improve reproductive performance during the summer. Given the complexity of heat‐stress effects on reproduction, comprehensive reproductive management during the summer is suggested i.e. combining two or more strategies in a program, might be more beneficial.
... The negative consequences of heat stress on the reproductive performance of dairy cattle are well documented. Heat stress may alter duration of estrus (Gangwar et al., 1965), uterine function (Collier et al., 1982), endocrine status (Collier et al., 1982;Wise et al., 1988;Wolfenson et al., 1988b;Howell et al., 1994), follicular growth and development (Wilson et al., 1998), and luteolytic mechanisms (Wilson et al., 1998). Extended periods of heat stress can also affect early embryonic development and survival (Biggers et al., 1987;Wolfenson et al., 2000;De Rensis and Scaramuzzi, 2003), fetal growth (Wolfenson et al., 1988a), and colostrum quality (Nardone et al., 1997). ...
Article
Animal welfare can be negatively affected when dairy cattle experience heat stress. Managing heat stress has become more of a challenge than ever before, due to the increasing number of production animals with increased milk yield, and therefore greater metabolic activity. Environmental temperatures have increased by 1.0°C since the 1800s and are expected to continue to increase by another 1.5°C between 2030 and 2052. Heat stress affects production, reproduction, nutrition, health, and welfare. Means exist to monitor and evaluate heat stress in dairy cattle, as well as different ways to abate heat, all with varying levels of effectiveness. This paper is a summary and compilation of information on dairy cattle heat stress over the years.
... In addition, among other factors, in HH, the high PP generates abundant forage growth with higher nutritional quality that affects positively the body condition of the heifers. In Holstein cows water spraying decreases respiratory rate and body temperature and improves the pregnancy rate (Wolfenson et al. 1988;Chen et al. 2015). In dairy cows from intertropical and subtropical zones, heat stress induced an increase in body temperature (Vasconcelos et al. 2011;Lima et al. 2013). ...
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The high climatic variability of hot climates of the intertropical zone reduces cattle fertility. In dairy cows in temperates zones, the THI has been used to evaluate the temperature and relative humidity (RH) joint effect in reproduction, but its use is not recommended in all geographic zones; in hot climates, the maximum temperature (Tmax) can provide more convenient information than THI. The objective of this study was to determine the artificial insemination (AI) service seasons and their joint effect with the maximum temperature and relative humidity of the previous seven days, the service day, and posterior seven days to the AI in the tropical milking criollo (LT) heifer’s gestation. Climatic data was used to define three seasons: hot-dry (HD), hot-humid (HH), and fresh-dry (FD), and 313 artificial insemination services from 176 heifers were analyzed over fourteen years. The seasons were determined by cluster analysis. Gestation at first service (GF) was analyzed with a logistic regression model and global gestation (GG) with a mixed linear generalized model. The Tmax of previous seven days insemination β̂1= − 0.20 ± 0.09 (p ≤ 0.02) in HD (p ≤ 0.02) and RH of seven days posterior insemination β̂2= − 0.08 ± 0.04 (p ≤ 0.04) in HD (p ≤ 0.01) affected GF. No effect of the Tmax and RH on the service day was observed (p > 0.05). The highest GG probabilities were higher than 0.70 in HH and FD, making those seasons the most suitable for inseminating LT heifers.
... En el periodo 2 los resultados fueron similares a los del periodo 1, ya que el tratamiento T 3 solo redujo en 0,37 y 0,38ºC la temperatura rectal con respecto a T 1 y T 2 (p<0,01). Diferencias superiores fueron reportadas por Her et al. (1988) con medias de 0,5 a 0,9ºC entre vacas con enfriamiento y sin enfriamiento, resultados similares también fueron reportados por Wolfenson et al. (1988). ...
Article
Full-text available
Las altas temperaturas afectan la reproducción del ganado bovino reduciendo la intensidad del estro y la fertilidad. Basado en lo anterior el objetivo del estudio fue evaluar los efectos de la inseminación artificial (IA) a tiempo fijo más un período corto de enfriamiento ambiental sobre la tasa de concepción y respuesta fisiológica de vaquillas bajo estrés calórico. Noventa vaquillas Holstein fueron distribuidas aleatoriamente en uno de los siguientes tratamientos: Un tratamiento testigo (T1) con detección visual de estro e IA mañana-tarde (n= 30); un segundo tratamiento (T2) bajo un protocolo de IA a tiempo fijo (n= 30) y un tercer tratamiento (T3) con el mismo protocolo de IA de T2 más un período de enfriamiento ambiental (ventilación y aspersión) de las vaquillas 11 d antes y 21 d después de la IA (n= 30). El experimento se dividió en dos períodos: el primero del 25 de junio al 26 de julio; el segundo del 15 de agosto al 16 de septiembre. En el primer periodo las vaquillas en T3 tuvieron una temperatura rectal (39,35oC) más baja (p
... During the summer months, heat stress is associated with decreased fertility, which could be attributed to a variety of factors including hormonal imbalances or reduced quality of oocytes, embryos and corpora lutea (reviewed by De Rensis, Lopez-Gatius, García-Ispierto, Morini, & Scaramuzzi, 2017). Grazing-based cattle systems should provide sufficient shade, and cattle housed indoors should similarly be provided with cooling systems such as sprinklers and ventilation that can reduce body temperature and increase fertility (Wolfenson, Flamenbaum, & Berman, 1988). ...
Article
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Using reproduction parameters as indicators for cattle welfare has limitations and, at best, these parameters should only be viewed as indirect indicators of welfare. On a farm level, measures such as fertility rates emphasize biological performance of the herd but fail to consider the welfare of individual animals. Even on an individual level, the relationship between reproductive effectiveness and animal welfare is complex. Good reproductive performance does not automatically signify good welfare, as domestication and targeted breeding programmes have led to prioritization of high productive and reproductive performance in most modern farm animal species. In this review, we synthesize literature regarding cattle husbandry, reproduction, welfare and their multidimensional relationships. We argue that practices such as artificial insemination or the use of sexed semen may provide potential welfare advantages as these practices reduce the risk of disease transmission and injury or enable selection of specific beneficial traits. Furthermore, they may offer a solution to current practices jeopardizing welfare, such as the management of surplus bull calves in the dairy industry. Conversely, the animals’ ability to perform natural behaviours such as oestrous expression, an aspect arguably contributing to welfare, is often limited on commercial farms; this limitation is particularly evident in housing systems such as tie stalls where movement is restricted. Moreover, common management practices such as oestrus manipulation may lead to negative attitudes in citizens who often regard naturalness as important element of animal welfare.
... Long-term exposure to heat stress may lead to reduced progesterone concentrations, however, because luteal concentrations of the hormone during the luteal phase have been reported to be lower in summer than winter (Howell et al., 1994). Additionally, cooling cows during the summer increased circulating concentrations of progesterone (Wolfenson et al., 1988). Some effects of heat stress on peripheral blood concentrations of hormones could be the result of changes in water balance during heat stress and reduced hematocrit (Richards, 1985;Lamp et al., 2015). ...
Article
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Heat stress causes a large decline in pregnancy success per insemination during warm times of the year. Improvements in fertility are possible by exploiting knowledge about how heat stress affects the reproductive process. The oocyte can be damaged by heat stress at the earliest stages of folliculogenesis and remains sensitive to heat stress in the peri-ovulatory period. Changes in oocyte quality due to heat stress are the result of altered patterns of folliculogenesis and, possibly, direct effects of elevated body temperature on the oocyte. While adverse effects of elevated temperature on the oocyte have been observed in vitro, local cooling of the ovary and protective effects of follicular fluid may limit these actions in vivo. Heat stress can also compromise fertilization rate. The first seven days of embryonic development are very susceptible to disruption by heat stress. During these seven days, the embryo undergoes a rapid change in sensitivity to heat stress from being very sensitive (2- to 4-cell stage) to largely resistant (by the morulae stage). Direct actions of elevated temperature on the embryo are likely to be an important mechanism for reduction in embryonic survival caused by heat stress. An effective way to avoid effects of heat stress on the oocyte, fertilization, and early embryo is to bypass the effects through embryo transfer because embryos are typically transferred into females after acquisition of thermal resistance. There may be some opportunity to mitigate effects of heat stress by feeding antioxidants or regulating the endocrine environment of the cow but neither approach has been reduced to practice. The best long-term solution to the problem of heat stress may be to increase genetic resistance of cows to heat stress. Thermotolerance genes exist within dairy breeds and additional genes can be introgressed from other breeds by traditional means or gene editing.
... This reduction may be associated with endocrine changes and the follicular microenvironment where the oocytes are exposed, leading to a lower development competence, which denotes the complexity of these mechanisms (ROTH, 2012). As an alternative, to solve the negative effects of high temperatures on reproductive performance, cooling methods should be used, such as sprinkling and ventilation, which can reduce RT of Holstein cows and, thus, improve CR (WOLFENSON et al., 1988). ...
Article
Summer heat stress lowers fertility in cattle in hot environments by influencing oocyte quality, follicular activity and progesterone (P4) level in blood plasma. However, the mechanisms by which elevated temperature influences corpus luteum function remain unclear. Elevated temperature has generally been known to upregulate the gene expression of heat-shock protein (HSP) 70 in a variety of cell types. To clarify the direct effects of elevated temperature on bovine corpus luteum function, we examined the expressions of HSP70, cell viability and the production of P4 and prostaglandins (PGs) in luteal cells cultured at 37.5 degrees C(normal temperature in our culture system), 39.0 degrees C(moderately elevated temperature) or 41.0 degrees C(severely elevated temperature) for 12 or 24 h. HSP70 mRNA expression was increased by incubation at 39.0 degrees C for 12 h and at 41.0 degrees C for 12 and 24 h, whereas HSP70 protein expression was not significantly affected. The viability of luteal cells cultured for 24 h, measured by flow cytometry with propidium iodide staining, was not significantly affected by temperature. Interestingly, the production of P4 by cultured luteal cells was higher at 39.0 degrees C than at 37.5 degrees C after 12 and 24 h of incubation. The production of PGF2 alpha was higher at 39.0 degrees C and 41.0 degrees C than at 37.5 degrees C after 12 and 24 h of incubation. The production of PGE2 was higher at 41.0 degrees C than at 37.5 degrees C after 24 h of incubation. The overall results suggested that elevated temperature does not negatively affect luteal function, and that the low fertility observed during summer is not due to a direct effect of elevated temperature on luteal cells.
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Heat stress has consequences on both the physiology and reproductive performance of cows, but the most dramatic effect for dairy producers is the decrease produced in fertility. The effects of heat stress on fertility include an increased number of days open, reduced conception rate, and larger number of cows suffering different types of anestrus. Once becomes pregnant, heat stress affects also the reproductive success of the cow through its direct effects on the ovary, uterus, gametes, embryo, and early fetus. This article reviews current knowledge of the effects of heat stress on fertility in dairy cows and the hormonal strategies used to mitigate these effects at the farm level. Administration of GnRH at the moment of artificial insemination can improve the conception rate. Breeding synchronization protocols for fixed-time insemination may reduce the calving conception interval and the number of services per conception. Progesterone-based protocols seem resolve better the reproductive disorders related to a hot environment (anestrus) than GnRH-based protocols. The use of combinations of GnRH, eCG, and hCG in progesterone-based protocols can improve results. Progesterone supplementation during the late embryonic and/or early fetal period would be useful in curtailing pregnancy losses, mainly in single pregnancies, whereas a more positive effect of treatment with GnRH than progesterone has been found in twin pregnancies. Melatonin therapy is emerging as a promising strategy to improve the natural reproductive performance of cows suffering conditions of heat stress. Copyright © 2015 Elsevier Inc. All rights reserved.
Article
The objective of the experiment was to examine the interaction of endophyte-infected tall fescue and environmental temperature on follicular and luteal development and function in beef heifers. Heifers were fed endophyte-free or endophyte-infected tall fescue seed at thermoneutral or heat stress temperatures (n = 6/treatment) 4 wk before and 3 wk after synchronized ovulation. All heifers were subjected to thermoneutral conditions (19°C, 50% relative humidity) from Days −7 to −2; temperature increased incrementally from Days −1 to 0 and cycled between 25°C and 31°C between Days 1 and 20 for heat-stressed heifers. Serum was collected and ovaries monitored every other day after induced luteolysis between Days 1 and 23 or until ovulation. Size and location of follicles >4 mm and corpora lutea were recorded. Serum concentrations of prolactin were reduced in heat-stressed heifers fed infected seed and both heat stress and infected seed decreased total cholesterol. Rectal temperature and respiration rate were greatest in heifers fed the infected seed when exposed to maximal temperatures. Heat stress led to reduced diameter of the corpus luteum and serum progesterone compared with thermoneutral conditions. Progesterone was reduced more so in heifers fed infected seed. The combination of infected seed and heat stress was associated with reduced diameter of the preovulatory dominant follicle, and consumption of infected seed led to fewer large follicles during the estrous cycle. Both stressors led to reduced serum estradiol. Impaired follicle function may explain reduced pregnancy rates commonly observed in heifers grazing infected tall fescue pasture.
Chapter
The fertility and reproductive efficiency of both male and female animals is very sensitive to climatic disturbances, particularly hyperthermia. The most evident consequences of heat stress are decreased quantity and quality of sperm production in males and compromised fertility in females. In this chapter, the effects of climate change on male and female reproduction have been separately and thoroughly elaborated. The effect of heat stress on embryo and fetal development has also been described. In the end, various approaches for mitigating the effects of heat stress on animals have been brought to light.
Thesis
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Female fertility is one of the most important economic drivers of cow-calf operations, however, the achievement of genetic improvement for female fertility traits is challenging due to the biological complexity of reproductive performance and the difficulties related to its statistical modeling. Among the traits relevant to beef cattle breeding practices, those related to key fertility events such as conception and calving are binary in nature. Traditional evaluations of binary traits involve the use of threshold models (TM) that convert categorical phenotypes to an underlying normally distributed range of genotypic values known as liabilities. Despite the successful influence that TM have had on genetic trends of categorically evaluated traits within livestock species, these models also have drawbacks. Among the most important weaknesses are their susceptibility to the extreme category problem (ECP) and their lack of flexibility to incorporate genomic information differently than using genomic relationship matrices whose inverse is difficult to obtain when the number of genotyped animals is high. These deficiencies of TM prevent them from comprehensively utilize all available phenotypic data and preclude their utilization in single-step genomic prediction methodologies based on marker effects models. Contrastingly, random regression models (RRM) have emerged as an attractive alternative for the evaluation of binary fertility traits in cattle due to their ability to overcome ECP problems and utilize all available information to produce more accurate results in comparison to TM. Furthermore, these models are flexible enough to accommodate any of the single-step genomic evaluation procedures that have been developed. Consequently, their extension to genomic evaluation procedures that avoid the need of inverting dense genomic relationship matrices such as the recently developed super-hybrid marker effects models, represents a novel approach to evaluate binary fertility traits in beef cattle. Traits like heifer pregnancy (HPG), first-service conception rate (FSCR) and stayability (STAY) constitute important elements of the breeding objective of beef cattle producers, therefore, they were selected as the traits to evaluate in this study. All the reproductive data utilized in this investigation was produced by the Angus cattle population of the John E. Rouse Colorado State University Beef Improvement Center (CSU-BIC). In general, this dissertation was divided in three different studies according to the physiological status of the females producing the phenotypic record (e.g., heifer vs. multiparous cows) and the number of instances that such phenotype can be recorded on the life of the animals (non-longitudinal vs. longitudinal). The first study involved the comparison of expected progeny differences (EPD) and genetic parameters obtained with TM and RRM in genetic evaluations of singly-observed heifer dichotomous fertility traits such as HPG and FSCR. Breeding and pregnancy ultrasound records of 4,334 Angus heifers (progeny of 354 sires and 1,626 dams) collected between 1992 to 2019 at the CSU-BIC were utilized. Observations for HPG and FSCR (1, successful; 0, unsuccessful) were defined by fetal age at pregnancy diagnosis performed approximately 130 d post artificial insemination (AI). Traditional evaluations for both traits were performed using univariate TM, whereas alternative evaluations were performed by regressing HPG (or FSCR) on age at first exposure (AFE) using linear RRM with Legendre Polynomials as the base function. Heritability (h2) estimates were 0.04 and 0.03 for HPG and FSCR using TM; whereas RRM derived h2 estimates were 0.02 and 0.006 for the average AFE for HPG and FSCR, respectively. Pearson and rank correlations between EPD obtained with each methodology were 0.97 and 0.96 for HPG, while for FSCR were 0.75 and 0.72, respectively. Regression coefficients from RRM predictions on those obtained with TM were 0.27 and 0.15 for HPG and FSCR, respectively. Differences in mean accuracies of prediction calculated at the average AFE were minimal between methodologies; however, RRM produced consistently higher accuracies than TM especially when considering young selection candidates. These results suggested that RRM genetic predictions for singly-observed fertility traits in beef heifers were feasible. More importantly, moderate to strong degrees of concordance were found between predictions obtained with both methodologies for both traits, implying that RRM could substitute for TM in genetic evaluations of heifer binary fertility traits. The second study focused on the comparison of EPD and genetic parameters yielded by TM and RRM in genetic evaluations for longitudinal binary fertility traits such as STAY and FSCR in multiparous Angus cows. Calving performance data, as well as, breeding and reproductive ultrasound records of Angus cows collected between 1990 to 2019 at the CSU-BIC were used for the study. Ten STAY endpoints defined as whether a cow calved at age 3, 4, and up to 12 yr given she calved as a 2-yr-old were assigned observations (1, successful; 0, unsuccessful). Similarly, ten FSCR age specific observations were assigned depending on the age of exposure of the females (ages ranged from 2 to 11 yr) and were defined by fetal age at pregnancy inspections performed approximately 130 d post-AI. Traditional evaluation for STAY was performed using a TM that only considered the success/failure of females reaching the age of 6 (STAY06), since this age is considered as the financial break-even point for cows within the beef industry. Conversely, given there is no specific age of interest for a multiparous cow to conceive in response to her first AI, the traditional evaluation for FSCR was performed using a repeatability TM. Alternative evaluations for both traits were performed by regressing each trait on its corresponding age specific endpoints using univariate linear RRM with Legendre Polynomials as the base function. Heritability (h2) estimates obtained for STAY were 0.10 and 0.04 for the TM and the RRM, respectively. In the case of FSCR, age was not a significant longitudinal descriptor for the trait; however, only with documentation purposes, h2 estimates were reported. For the TM the h2 estimate was 0.03 whereas for the RRM, heritabilities ranged between 0.02 to 0.05 for all the ages at exposure considered in the model. Pearson (rp) and Spearman’s (rs) correlations between EPD obtained with each method for STAY were 0.84 and 0.86. For FSCR, correlations were calculated between the EPD obtained with the repeatability TM and each one of the age-specific EPD obtained with the RRM; therefore, results for the rp ranged between 0.70 to 0.99; whereas results for rs ranged between 0.69 to 0.99, depending on the age of exposure considered in the RRM. Although mean accuracies of prediction were higher using RRM than using TM for both traits, increments were much more relevant for STAY than for FSCR. The strong degrees of concordance found between predictions obtained with both methodologies for STAY, suggests that RRM could effectively substitute TM in genetic evaluations of this trait. For FSCR, no improvements were achieved by evaluating the trait using RRM, mainly due to the lack of influence that age had on the ability of cows to conceive in response to their first AI at any age. Finally, the third study had as objectives 1) to explore the feasibility of implementing single-step random regression super-hybrid models (ssRR-SHM) for the genomic evaluation of HPG, FSCR and STAY; 2) to assess the impact of differing data structures in the resulting genomic predictions of ssRR-SHM for all traits; 3) to identify quantitative trait loci (QTL) associated with the binary fertility traits contemplated in this dissertation. Two types of genetic evaluations were implemented for each trait, the first type was a pedigree-based RRM that utilized Legendre polynomials as the base function in where the phenotype of interest was regressed on an appropriate age covariate. The second evaluation type was a ssRR-SHM that also used Legendre polynomials as the base function and regressed observations of the trait of interest on its appropriate age covariate, but that included random effects of marker and extra polygenic effects. Within each trait, four different data structure scenarios were created depending on the phenotypic performance of the genotyped and non-genotyped subsets of animals. The behavior of the genomic predictions was assessed through the calculation of Pearson and Spearman’s correlations and the estimation of the regression coefficients of EPD obtained with the ssRR-SHM on those obtained with their corresponding pedigree-based RRM. Results of this study indicated that the implementation of ssRR-SHM for the genomic evaluation of singly-observed binary fertility traits like HPG and FSCR, as well as for the evaluation of a longitudinally recorded binary trait such as STAY was feasible. Nonetheless, an overestimation of genomic predictions occurred with these models when phenotypic records of pre-selected genotyped animals were included in the evaluation. Additionally, inaccurate imputation of genotypes for non-genotyped animals also impacted resulting genomic predictions, although this issue was restricted to this subgroup of animals only. In all cases, the removal of phenotypic records from preselected animals and the maintenance of closely related individuals in the pedigree ameliorated problems associated to overestimation of genomic predictions and improved correlations among genomically-enhanced and pedigree-based EPD for all traits. Regarding GWAS analyzes, the application of ssRR-SHM identified single nucleotide polymorphisms that resulted located either within or relatively close to genes that have been previously associated with important reproductive processes and fertility traits in cattle.
Chapter
The nutritional, physiological, and reproductive function has detrimental effects on heat stress, which is found in many species of mammals. High ambient temperature in mammals cause a decrease in the length and intensity of estrus by disturbing ovarian function as well as decreasing pregnancy rate after artificial insemination. The effects of nutritional stress on developing oocytes in the ovarian follicle and in the reproductive tract on early embryos are because of the environment where a breeding female lives before conception and at the early stages of pregnancy. Maturity of oocyte, blastocyst yield, prenatal survival, and the number of offspring born alive are affected by change in consumption and quantity of the food taken during the pre-mating period. To improve reproductive efficiency and offspring quality, it is necessary to detect and evaluate the deteriorating effects of heat stress on reproductive organs and cells and to plan nutrition related strategies.
Conference Paper
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RESUMO-São muitos os fatores que contribuem para o aumento dos efeitos do estresse térmico como, produtividade, raça e sistema de criação. Desta forma, objetivou-se com o presente trabalho realizar uma revisão bibliográfica com o intuito de destacar a importância da ambiência no desempenho produtivo de vacas leiteiras. A combinação da alta temperatura e a elevada umidade relativa do ar pode prejudicar a dissipação de calor corporal. Animais em estresse térmico podem apresentar alterações comportamentais e fisiológicas. A mensuração da frequência respiratória, frequência cardíaca, temperatura superficial e temperatura retal (temperatura interna) são ferramentas que podem ser utilizadas para diagnosticar o estresse térmico em bovinos. Sendo assim, a climatização pode ser utilizada proporcionando aos animais um ambiente com temperaturas mais amenas, evitando situações de estresse térmico e possibilitando que os animais expressem seu potencial produtivo.
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Reproductive management in high producing dairy cows is difficult because many fertility factors determine success. These many factors do not exert themselves with the same influence on fertility. Further, the degree to which each factor can be controlled varies greatly. Organizing fertility factors into groups that reflect their control enables reproductive management teams to focus on the most important factors and to exert positive influence. Factors controlling fertility can be subdivided into three distinct groups that reflect the degree to which each can be controlled. These groups are fertility factors controlled by humans, those controlled by the reproductive system of the cow, and those factors natural (intrinsic) to any herd. The most control can be exerted by factors controlled by humans, and there can be intermediate influence on factors controlled by the reproductive system of the cow. Very little control can be exerted on fertility factors intrinsic to each herd. Management effort should be focused on those factors over which control can be exerted and where there is a high probability of success.
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A field trial was conducted to evaluate the effects of bovine somatotropin (bST) on estrous characteristics of multiparous, lactating Holstein cows (n = 44) during the summer months. Cows were randomly assigned to receive bST every 14 d or no bST (control) and were fitted with a HeatWatch® transmitter (HW; DDx Inc., Denver, CO). A temperature-humidity index (THI) was calculated for the day of estrous onset. Ranges of THI were 68 to 80 (THI < 72 = THI 1 [no heat stress], THI 72 to 76 = THI 2 [mild heat stress], THI > 76 = THI 3 [moderate heat stress]). Duration of estrus, number of standing events, and quiescent periods between standing events were similar (P>0.10) between bST and control cows. The number of standing events was influenced (P<0.05) by THI and averaged 20.3 ± 3.0, 8.6 ± 1.3, and 8.9 ± 1.2 for THI 1, THI 2, and THI 3, respectively. Quiescent periods observed between standing events tended (P=0.11) to be influenced by THI and were 1.2 ± 0.8, 3.0 ± 0.4, and 3.0 ± 0.4 h for THI 1, THI 2, and THI 3, respectively. Days to first service were less (P=0.07) for bST-treated cows (90.9 ± 5.1 d) than for control cows (105.9 ± 6.1 d). First service conception rates and pregnancy rates were similar (P>0.10) between bST-treated and control cows. We conclude that estrous characteristics and pregnancy rates of lactating dairy cows were not influenced by bST treatment. However, the number of standing events was reduced, and quiescence between mounts tended to increase, in lactating dairy cows as ambient temperature and humidity increased.
Chapter
Heat stress induces infertility in farm animals and represents a major source of economic loss to the livestock sector. The decrease in animal fertility is caused by elevated body temperature that influences ovarian functions, oestrous expression, oocyte health and embryonic development. Protection from heat stress during dry period is particularly crucial for a high-producing cow since it involves mammary gland involution and subsequent deve­lopment, rapid fetal growth and induction of lactation. Cows and cycling buffaloes under heat stress have lower plasma inhibin concentrations, reflecting reduced folliculogenesis, since a significant proportion of plasma inhibin comes from small- and medium-sized follicles. Concentrations of plasma FSH are higher during the preovulatory period in summer and are associated with lower circulating concentrations of inhibin. The neuroendocrine mechanisms controlling gonadotrophin secretion are more sensitive to heat stress particularly in animals with low concentrations of plasma oestradiol. Environmental temperature and humidity 2 days prior to insemination is critical for conception than at any other phase of the reproductive cycle. A rise in rectal temperature diverts blood from the visceral organs to the peripheral circulation due to redistribution of blood to alleviate heat, which could reduce perfusion of nutrients and hormones to the endometrial and oviductal tissues affecting reproductive functions. In terms of steroid production, the thecal cells are more susceptible than granulosa cells to heat stress and express a delayed effect of heat stress in both medium-sized and preovulatory follicles. A rise in testicular temperature in bulls similar to other mammals with external testes leads to reduced sperm output, decreased sperm motility and an increased proportion of morphologically abnormal spermatozoa in the ejaculate. X and Y spermatozoa are affected differentially by high temperature. The plasma concentrations of insulin, IGF-I and glucose are low in summer months compared to winter months () probably because of low dry matter intake and increased negative energy balance. Insulin is required for the development of follicles and has beneficial effects on oocyte quality. Genetic selection for heat adaptability, both natural and artificial, is likely to modulate the impact of heat stress on reproductive functions, and therefore, genetic selection for thermal tolerance may be a necessity under climate change conditions.
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A number of measurable physiological events characteristically occur and cause changes during the perioestrual period including the classical, diagnostic sign of standing behaviour. The onset of oestrus coincides with peak titres of oestradiol-17β that subsequently induce the preovulatory surge of LH within 1 to 3 h and ovulation of a mature follicle some 24 to 32 h after the onset of oestrus. Although detection efficiencies are consistently greater in higher producing herds, oestrus-detection efficiency generally has declined in recent years as herd size and milk production have increased. New technologies have introduced some needed assistance for detecting cows in oestrus. These include various in expensive heat mount detectors to more sophisticated electronic gadgetry, such aspedometry and radiotelemetric sensors that detect temperature, tissue impedance, and pressure. Oestrus detection aids are usually more efficient but not necessarily more accurate than visual observation. Differences in housing and environmental conditions, in addition to labor inputs, costs, and efficacies, result in variable acceptance of such technologies. Detection efficiency and accuracy can be improved by simultaneous use of synergistic technologies; those that compliment each other and monitor different indicators of oestrus. Combining technologies for simultaneous measurements of several physiological events associated specifically with the onset of oestrus and their radiotelemetrically signaling to a central computer for subsequent analysis should provide greater efficiency ofoestrus detection with fewer false positives. The ultimate goal of determining the onset of oestrus or ovulation is to predict the optimal timing for insemination. Ultimately, herd personnel must interpret information gathered by these technologies and judge whether or not and when to inseminate cows based on their visual inspection of identified cows.
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To study the duration, intensity and behavioural signs of oestrus in Holstein heifers and cows in a grazing system, 15 heifers and 33 milking cows were used. Both groups were synchronised with two Prostaglandin F2 alpha treatments 14 days apart, after what animals were observed continuously for 6 days. Activities recorded were: butting, flehmen, restlessness, sniffing the vulva, chin resting, mounted but not standing, mounting (or attempt) other cows, and standing to be mounted. Duration of oestrus was different in heifers than in cows (9.9 +/- 1.8 vs. 13.5 +/- 2.0 hours), as average number of mounts (48.2 +/- 13.4 vs. 26.8 +/- 3.6), and mounting intensity (5.6 +/- 0.8 vs. 2.5 +/- 0.5). The interval between the first accepted mount and ovulation (determined by ultrasonography) was 29.1 +/- 3.9 in heifers and 26.9 +/- 3.7 in cows, and between the last accepted mount and ovulation of 19.3 +/- 3.9 in heifers and 12.7 +/- 2.6 hours in cows. Both categories started the activities with butting, sniffing, flehmen, chin resting, to continue with mounting. In heifers the activity started earlier in the proestrus, while in cows started closer to oestrus. Best observation periods were at dawn and at dusk, and worst were when animals prioritized other activities like eating or milking. More observation and longer daily periods are more efficient in the detection of heat.
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The effects of season on the fertility of the dairy cow added to the metabolic stress of milk production are well known. We here present lactating dairy cows as a comparative model of this problem. This review examines the results of recent studies that have highlighted heat stress (HS) effects on pre-ovulatory follicles. From these studies, we draw information regarding the mechanisms giving rise to temperature gradients across reproductive tissues. Our review is completed by a discussion of approaches designed to reduce the negative effects of HS based on cooling strategies implemented before ovulation at or around estrus.
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Forty pregnant F 1 crossbred cows (20 Holstein-Friesian × Boran and 20 Simmental × Boran) were assigned to a 2 × 2 (work × diet) factorial experiment as follows: supplemented-non-working (SNW), supplemented-working (SW), non-supplemented-non-working (NSNW) and non-supplemented-working (NSW). Working cows pulled sledges 100 days/year (pull = 350 to 450 N, 4 h/day, 4 days/week). Conception and oestrus at fixed times (200 and 365 days post partum ) were analysed using linear logistic models. Proportional hazard models were used for analysing ‘failure’ time data such as time to first oestrus or time to conception. Diet supplementation significantly decreased days to first oestrus and days to conception in non-working and working cows. SW cows had similar reproductive performance to NSNW cows. In supplemented cows, work significantly delayed days to conception. However, by 365 days post partum , conception rate was similar for SNW and SW cows. Body condition at calving significantly affected post-partum reproductive ability of non-working and working cows. Natural grass hay alone could not support potential reproductive ability of crossbred cows. Work output of supplemented cows may be associated with longer calving intervals. The economic trade-offs between longer calving intervals and work output should be examined in detail.
Chapter
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6 Universidade de Évora UE, Évora-Portugal, vfc@uevora.pt RESUMO-São muitos os fatores que contribuem para o aumento dos efeitos do estresse térmico como, produtividade, raça e sistema de criação. Desta forma, objetivou-se com o presente trabalho realizar uma revisão bibliográfica com o intuito de destacar a importância da ambiência no desempenho produtivo de vacas leiteiras. A combinação da alta temperatura e a elevada umidade relativa do ar pode prejudicar a dissipação de calor corporal. Animais em estresse térmico podem apresentar alterações comportamentais e fisiológicas. A mensuração da frequência respiratória, frequência cardíaca, temperatura superficial e temperatura retal (temperatura interna) são ferramentas que podem ser utilizadas para diagnosticar o estresse térmico em bovinos. Sendo assim, a climatização pode ser utilizada proporcionando aos animais um ambiente com temperaturas mais amenas, evitando situações de estresse térmico e possibilitando que os animais expressem seu potencial produtivo. Palavras-chave: conforto térmico; bovinocultura leiteira; bem-estar; construções rurais. INTRODUÇÃO Os bovinos da raça Holandesa destacam-se por serem animais de grande porte, peso elevado, com alta taxa de ingestão de matéria seca, elevada produção leiteira, possuem boa habilidade materna, úbere grande, e ligamentos fortes para sustentação do grande volume de leite, porém são dependentes de temperatura amena (PASSETTI et al., 2016). Pesquisadores vêm dedicando suas atenções para produção de leite, buscando solucionar os mais diversos problemas da produção, relacionando ambiência com a nutrição. Chandler (1987) e West (2002) obtiveram respostas, que variam em função de
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Global warming seems more probable, whether as gradual warming or increased frequency of warmer episodes. The productivity of cattle in temperate countries will decline unless counteracting steps are adopted. The probability of pre-emptive breeding for maintaining temperate breed performance coupled with heat stress tolerance is too low to be adopted for counteracting warming. The expected warming will mostly involve temperature increases. These will indirectly affect radiant heat gain in animals owing to reduced radiant heat dissipation from the body by convective heat loss, which results in an increased sensitivity to incoming radiant heat at higher air temperatures. These necessitate an emphasis on increasing convective heat loss by structure design and forced air flow by fans. Convective heat loss diminishes with increasing air temperatures. Evaporative heat loss remains the alternative. Evaporative cooling of the ambient requires partial enclosing of the space surrounding the animals and is limited by the humidity in ambient air. An alternative was developed of coupling forced ventilation with wetting of animal surface. The exchange of ambient air flowing on animal surface makes the evaporation practically independent of air humidity and the loss of heat from animal surface practically independent of the surface to air temperature gradient. The coupling of forced ventilation with wetting combination may be attained in various parts of the dairy farm, the holding area of the milking parlour, the feeding trip and the resting area. Each of these requires differing structural and technological adaptations. Climate and farming systems vary between locations which require specific solutions.
Chapter
Activation of the hypothalamic–pituitary–adrenal axis and the consequent increase in plasma glucocorticoid concentrations are two of the most important responses of the animals to heat stress. The short- and long-term environmental heat affects endocrine glands and in turn release of hormones, namely, thyroxine, cortisol, growth hormone and catecholamines. Some of them result in initial increase due to acute stressors and a decline in plasma levels after prolonged exposure to stressors has been observed. The relationship of amounts in plasma of these hormones to milk production appears to be related directly for cortisol, growth hormone and prolactin with an inverse relationship with thyroxine. Epinephrine and norepinephrine are elevated with prolonged environmental heat stress. Hormones in plasma are important as potential indicators of the physiological status of a cow and reflect the physiological compensations a cow undergoes at various stages of lactation and exposure to heat stress. The plasma thyroxine (T4) and triiodothyronine (T3) levels have been observed to decline under heat stress as compared to thermoneutral conditions. The decline in thyroid hormones along with decreased plasma growth hormone (GH) level has a synergistic effect to reduce heat production. A reduced secretion of GH is required for survival of the homeotherm during heat stress. The concentration of insulin-like growth factor-1 (IGF-1) has been observed to decrease during the summer months. Aldosterone concentration declines due to a fall in serum K levels and increased excretion in sweat during heat stress. Heat stress has a detrimental effect on animal reproduction partly by disrupting the normal release of gonadotrophin-releasing hormone from the hypothalamus and luteinising hormone (LH) and follicle-stimulating hormone from the anterior pituitary gland. Heat stress reduces the degree of dominance of the selected follicle as reduced steroidogenic capacity of its theca and granulosa cells and a fall in blood oestradiol concentrations. Plasma progesterone levels may be increased or decreased depending on whether the heat stress is acute or chronic and also on the metabolic state of the animal. Insufficient progesterone secretion by the corpus luteum during summer is a probable reason of low fertility in cattle and buffalo during summer months in tropical climates.
Article
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Hereford and Hereford X Angus cows (n = 31) were utilized to determine the effects of heat stress on early embryonic development and survival. After acclimation to handling, cows were cannulated via the jugular vein on d 7 and assigned to either a control (C) chamber environment of 22 C, 35% relative humidity (RH) or one of two heat stress treatments. Ambient temperature was maintained at 37 C for 12 h followed by a decrease to 33 C for the remainder of the day in both treatment groups. Relative humidity was maintained at 27% in treatment 1 (TRT 1) and 38% in treatment 2 (TRT 2). On d 8 to 16, daily measurements of respiration rate (RES), rectal temperature (REC) and water intake were taken along with samples of blood, which were analyzed for hematocrit (HEM) and plasma concentration of protein (PP), progesterone (P4), estradiol-17 beta (E2), thyroxine (T4) and glucose (GLU). The uterus was recovered and flushed with saline on d 17 to recover the conceptus and uterine contents. Conceptus (if present) and corpus luteum (CL) wet weight were determined. Cows subjected to TRT 2 had increased RES and REC (P less than .01), while HEM was decreased (P less than .05) compared with C cows. Plasma T4 concentration was decreased (P less than .10) in TRT 2 compared with TRT 1 and cows, while P4 concentration were not significantly different. Corpora lutea wet weights were reduced (P less than .10) in heat-stressed cows vs C cows.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
Lactating cows (116) were assigned randomly to shade or no shade treatments during the summers of 1974 and 1975. Shade structure was 9.1 × 24.4 m with an insulated metal gable roof and floor of reinforced concrete. Feed and water were available under the structure, and cows had free access to adjacent bermudagrass sod. Black globe temperature was the climatological response that differed among treatments (shade = 28.4 C, no shade = 36.7 C). Respirations/min (54<82) and rectal temperatures (38.9 C<39.4 C) were lower for shade cows. Least squares means for milk yield, considering variability due to treatment, year, treatment-year, breed, breed-treatment, year-breed, year-breed-treatment, cows in year-breed-treatment, week of experiment, and days pregnant, were 16.6 and 15.0 kg/day for shade and no shade, a 10.7% effect. Lactation curves were heterogenous. Conception rates were 44.4% (54 services) and 25.3% (75 services) for shade and no shade. Results suggest improvement in reproduction and lactation from providing shade structure.
Article
Rabbits were heat-stressed during two definite stages of pregnancy: 1. during early stages of blastocyst formation and rapid growth of the corpus luteum (Days 3–5), and 2. during implantation period (Days 6–8). Hyperthermia was created (+ 1.2°C) in which food intake was reduced to 1/3 of control. Both treatments, H(3–5) and H(6–8), reduced conception rate to 59% from 74% of the control. The development of the remaining live embryos was retarded in the H(3–5) group only.Plasma progesterone concentration in the H(3–5) group was significantly lower than in the control, immediately following termination of heat exposure. In the H(6–8) group, progesterone was only slightly changed, as compared to control. Histological examination of the ovarian corpus luteum indicated that size and number of the large luteal cells were reduced in both heat-stressed groups, as compared with the control.These results indicate that: (a) rabbit embryos are more susceptible to heat stress during blastocyst formation than during implantation, (b) ovarian function impairment is more pronounced during the rapid linear growth stage of the corpus luteum (Days 3–5), and (c) a possible link between impaired ovarian function and reduced reproductive performance can be suggested.
Article
Two groups (five animals each) of 12- to 15-month-old virgin Holstein heifers were used to evaluate the effects of natural and controlled hot and cool climatic conditions in a 180-day experiment on certain reproductive and physiological responses.Under cool climatic conditions (62 to 65 F), the average length of the estrous cycle was 20 to 21 days, as compared with 25 and 21 days under controlled, cycled hot (75, 85, and 95 F), and natural summer climatic conditions, respectively. The difference in responses under hot and cool climatic conditions was highly significant (P < 0.01). Under spring, cycled hot, air conditioning, and natural summer climatic conditions the average duration of estrus was 20, 11, 20, and 14 hr, respectively. Thus, hot climatic conditions significantly (P < 0.01) depressed the length of the estrual period. The incidence of clinical anestrous was 33% among the heifers during the cycled, hot period (in climatic chamber). The intensity of estrus and post-ovulatory bleeding time were decreased under hot climatic conditions.Thyroidal activity was depressed on the day of estrus in contrast to other days of the estrous cycle. Neutrophila, lymphopenia, and general leucocytosia (P < 0.01) were observed on the day of estrus.
Article
The relationship between fatty liver and reproductive performance was investigated in a commercial herd of Guernsey dairy cattle. Forty-two cows were sampled by liver biopsy at 1 week after calving, and divided into two groups, a fatty liver and a non-fatty liver group, on the basis of the level of liver fat. The cows in the fatty liver group had a milk yield of 5267 kg and a calving interval of 428 days compared with 4407 kg and 369 days for the cows in the non-fatty liver group. The reduced fertility was associated with an elongation in the interval from calving to first service of 20 days and with a reduced conception rate. The occurrence of fatty liver significantly impaired the reproductive performance of the cows.
Article
Thirty-two cows were provided with 115% of their maintenance digestible en- ergy requirements (low-prepartum) during the last sL-~ to eight weeks of gestation for comparisons with 32 cows fed 160% of their maintenance energy needs (high- prepartum). The 64 cows were factorially assigned to two energy levels postpartum. One group was fed alfalfa hay at 2% of body weight and enough concentrates to maintain relatively constant body weights through a complete lactation (high-post- partum). A second group was fed alfalfa hay at 2% of body weight and enough con- centrates to satisfy the National Research Council energy recommendations of 1958 (low post-partum).
Article
Rectal temperatures and hormone concentrations were monitored at intervals of 2 to 3 weeks, and milk, milk fat, and California mastitis test scores at intervals of 1 week in five shaded and in four nonshaded early lactation cows. Measurements were taken from September to December in the mildly heat stressing climate of Oahu, Hawaii. The daily ambient temperature flux ranged from 22 C to 29 C in September to 20 C to 25 C in December. Average daily temperature-humidity index (THI) values were 75 to 70 for September and December, respectively. Average daily THI values were correlated with rectal temperatures in nonshaded cows and were negatively correlated with plasma adrenal cortex hormones (corticoids) in shaded cows, plasma thyroid hormone in shaded and nonshaded cows, and with milk production in nonshaded cows. Estimated milk production decline per unit increase in THI was 0.32 kg. Nonshaded cows had higher rectal temperatures, a trend for lower plasma corticoids, produced less milk and milk fat, and had higher California mastitis test scores. Shaded cows maintained a higher fat percentage at THI above 74. Average plasma thyroid hormone values were not different between treatment groups. Both groups failed to attain normal rectal temperatures at night. Afternoon rectal temperatures were more highly correlated with the rectal temperature with which the cow started the day than they were with the THI of the day itself.
Article
Data representing 5,062 services during 1960 to 1971 in the Florida Agricultural Experiment Station dairy herd were analyzed by least squares to delineate factors affecting conception rates. Overall conception rate was 37.9%. From a set of 21 climatological measurements, the five selected as most important ranked (1) maximum temperature day after insemination, (2) rainfall day of insemination, (3) minimum temperature day of insemination, (4) solar radiation day of insemination, and (5) minimum temperature day after insemination. Warm months were more closely associated with lower conception rates than were cool months (33.7 compared to 40.1%); month effects appeared to be accounted for by the climatological measurements. Conception rates declined with age: heifers, 47.6%; young cows, 42.7%; older cows, 31.9%. No decline with advancing service number (1 to 5) occurred. Service sire and inseminator effects were detected as expected. Although breeds differed (Aryshires, 33.8; Brown Swiss, 34.6; and Guernseys, 37.0; Holsteins, 35.5; and Jerseys, 48.4%), there was no evidence of breed (Jerseys and Holsteins) by month or breed by season interactions nor was it possible to detect age by season interactions.
Article
Plasm progesterone and cortisol were measured in jugular blood by competitive protein-binding assay. Six cycling, estrus-synchronized Guernsey heifers were followed for four consecutive estrous cycles under two controlled temperature (18.2 C, 55% relative humidity; and 33.5 C, 55% relative humidity) conditions. Prolonged exposure to heat of Guernsey heifers increased plasma progesterone on days 2 to 19 of the first cycle and only on days 2 to 8 of the second cycle. However, heat stress depressed plasma cortisol in both cycles and reduced the correlation coefficient between these steroids relative to specific stages of the estrous cycle.
Article
Effects of cooling high producing dairy cows during the dry period were examined in 84 pluriparous Israeli-Holstein cows. Cooling was by a combination of wetting and forced ventilation from 0600 to 1800 h until parturition and common management afterwards for both groups. Cooling maintained diurnal increase in rectal temperature within .2 degrees C as compared with .5 degrees C in control cows in warmer months, Mean rectal temperatures at 1400 h in control cows were moderate, within 39.2 degrees C. Cooling did not affect prepartum or postpartum body condition score or mean blood progesterone during the dry period. Results suggested a possible increase in blood progesterone in later pregnancy by cooling during hot weather. Cooling increased mean 150-d milk production by 3.6 kg/d (3.1 kg FCM/d). Prepartum cooling negatively affected first lactation month yield in cows calving in early summer. Prepartum cooling might prevent adaptation to heat and impair subsequent postpartum performance. Prepartum progesterone was not related to milk yield. Calves' birth weight increased by cooling, but the effect was mostly in older cows. Birth weight was related to milk yield, independently of cooling effect, mostly in older cows. Cooling during the dry period might increase milk yield as it does during lactation. Results indicate possible benefit of cooling dry cows even under mild heat stress.
Article
Effect of cooling on body temperature, milk production, estrous behavior, and reproductive performance was examined in 66 estrous-synchronized, Israeli-Holstein dairy cows. Cooling was by an automated system, which actuated sprinkling (30 s) followed by forced ventilation (4.5 min) for 30-min periods. Cows were cooled 9 times/d between 0500 and 2100 h over 10 d, starting 1 d before expected estrus until d 8 post estrus. Cooling reduced typical diurnal rise of body temperature in summer heat-stressed cows by .5 to .9 degrees C, and body temperature was maintained close to normothermic temperature (38.6 degrees C). Milk production of cooled cows was 2.6 kg/d (+8%) above control at end of the cooling period. More cooled cows than noncooled exhibited standing estrous behavior; in noncooled cows, silent ovulations or anestrus were more frequent. Conception rate of cooled cows did not differ from control, suggesting need for a longer than a 10-d cooling period for improvement of fertility. The cooling system has potential to alleviate heat stress in dairy cows and to improve their thermal balance, productive, and reproductive performances.
Article
A method for cooling dairy cattle based on repeated wetting to attain maximal water trapping in the coat, followed by its rapid evaporation by using forced ventilation has been examined. Effects examined include duration of wetting, duration of cooling, and density of the animals in the holding area. The coat was wetted by inverted static sprinklers. Also examined was the extent to which the diurnal increase in rectal temperature can be prevented. The maximal decrement of temperature was attained at 30 min after cessation of cooling in all trials. Wetting the coat for 10 s was less effective than for 20 or 30 s; the latter did not differ in their effects. Cooling animals for 15, 30, and 45 min produced decrements in temperature of .6, .7, and 1.0 degrees C, respectively. Maintaining animals at a density of 1.9 m2/cow in the holding area reduced to about half the decrement as compared with a density of 3.5 m2/cow. When cows were cooled 5 times per day for 30 min, temperatures were maintained within 38.2 to 38.9 degrees C during the day, which were significantly lower than for those not cooled.
Article
The breeding records and meteorological data for cows with first services between July 1, 1979, and June 30, 1980, in a large Florida herd were analyzed to determine the relationship between temperature and breeding efficiency. Seasonal high environmental temperatures were associated with low breeding efficiency. Increased maximum temperature from 29.7 degrees C during April to 33.9 degrees C during July was associated with a decrease in conception rate on first service from 25 to 7%. Also, the average number of inseminations per conception, based on pregnancy diagnosis 6 to 8 wk after breeding, was higher from May to August (4.5 to 5.3) than from September to April (2.3 to 3.5). Days open were longer for the cows first inseminated during May, June, and July (173, 171, and 167 days, respectively) than during other months (99 to 149 days). Temperature decreases of any magnitude for 1 to 3 days before or after the day of breeding, when maximum temperatures on the day of breeding were greater than or equal to 27 degrees C, were associated with higher pregnancy rates. Also, similar temperature decreases around the time of breeding, below the previously mentioned high maximum temperatures for 20 days before the day of breeding, were accompanied by higher conception rates. Fertility was consistently lower under all temperature changes when maximum temperatures on the day of breeding were greater than or equal to 33 degrees C.
Article
Conception rates of a Holstein dairy herd near Culiacan on the west coast of Mexico were evaluated with respect to the average temperature-humidity index of the 2 days prior to breeding, the day of breeding, and the day following breed- ing. Average daily index for 3 yr ranged from 62 to 86. Average daily ambient temperature and relative humiditv for indexes 76 and 82 were 26.5 C," 68% and 29.7 C, 75%. Conception rates for 191 cows serviced on days with an av- erage index under 66 was 67% as com- pared to 21% for 818 cows serviced on days averaging above 76. The average temperature-humidity index of the 2nd day prior to breeding was the most re- lated to conception rate. Conception rate declined from 55 to 10% as the average index of this day increased from 70 to 84 (r = --.995). Between 68 and 82 the average conception was 42.3% ff the average index of the 2 days prior to breeding was less than on the day of breeding. Conception rates averaged 10.4% lower (31.9%) ff the index of the 2 days prior to breeding was higher than on the day of breeding indicating that temperature~humidity of individual days prior to breeding influenced breed- ing efficiency.
Article
Environmental and genetic effects on reproductive performance were estimated. Data included records of 194,579 inseminations of cows and 56,132 inseminations of heifers in 200 kibbutz herds from 1980 to 1981. Conception status was ascertained by veterinary palpation if no subsequent parturition was recorded. With subsequent parturition, the insemination closest to 277 days before parturition was considered successful. Largest differences in conception rate were between cows (40.4%) and heifers (64.3%) and among insemination month for cows (23.5 to 51.5%). Heritabilities of sire effect on conception rate were .016 for cows and .006 for heifers. Correlations between heifers and cows were .64 for inseminator and .54 for service sire. Low correlation between heifers and cows for herd effect (.17) indicates a management problem; low correlation between heifers and cows for sire effect (.27) suggests a different genetic mechanism for fertility. Significant improvement may be achieved in fertility by selection of service sires, sires, and inseminators if evaluations are based on a large number of observations. However, the major increase of conception rate may be expected from reducing adverse effects of summer conditions on reproductive performance.
Article
The effects of high dietary protein concentrations, high ambient temperatures and low dietary beta-carotene levels on fertility and on plasma progesterone and oestradiol-17 beta levels in high-yielding dairy cows, are described. High-yielding dairy cows were fed diets containing 15 or 20% crude protein. Cows fed the higher level of protein were less fertile and had a lower plasma progesterone concentration during the oestrous cycle preceding the first insemination. This phenomenon was especially pronounced in cows fed a diet containing 85% concentrates and 15% hay, where plasma progesterone levels during days 9-17 of the oestrous cycle were 2.5-3.7 ng/ml in cows fed the high level of protein and 4.0-5.5 ng/ml in cows fed the low level of protein (P less than or equal to 0.05). In cows fed 50% more energy before parturition, plasma progesterone levels did not differ between animals fed the low and high protein diets. Heat stress, which caused a rise in body temperature, decreased fertility and plasma progesterone levels during the luteal phase of the oestrous cycle but increased plasma oestradiol-17 beta levels during the 36 h preceding the onset of oestrus from 5 to 7 pg/ml (P less than or equal to 0.005). The effect on fertility of supplementing the diet of dairy heifers and cows with beta-carotene is reviewed. In some of the experiments where the basal plasma beta-carotene levels were lower than 50 micrograms/100 ml, beta-carotene supplementation significantly increased fertility. However, in no case was fertility affected when plasma beta-carotene levels exceeded 150 micrograms/100 ml. The possible relationships among body weight changes, energy balance, plasma progesterone levels and fertility of dairy cows are discussed.
Article
Holstein heifers (n = 29) were used to determine whether thermal stress during the first 7 d of embryonic development may increase the incidence of embryonic abnormalities in dairy cattle. Heifers were acclimated to environmental chambers at 20 degrees C for 9 d and superovulated with follicle stimulating hormone-pituitary (FSH-P; 40 mg total), beginning on Days 9 to 11 of the estrous cycle. Prostaglandin F(2)alpha (Lutalyse; 50 mg total) was administered on Day 3 of FSH-P. Heifers were inseminated artificially at estrus and then maintained at either thermal neutrality (20 degrees C) or under hyperthermic conditions (daily exposure up to 16 h at 30 degrees C and 8 h at 42 degrees C) for 7 d beginning at 30 h after the onset of estrus. On Day 7 post estrus, embryos were recovered nonsurgically and evaluated morphologically for stage of development and quality. The distribution of embryos classified as normal, abnormal, retarded or as unfertilized ova, differed (P<0.001) between heat stress and thermoneutral treatments. Only 20.7% of 82 embryos recovered from stressed heifers were normal compared with 51.5% of 68 embryos from thermoneutral animals. Stressed heifers had a higher incidence of abnormal and retarded embryos with degenerate nonviable blastomeres. Responses indicated that thermal stress from 30 h after the onset of estrus to Day 7 post estrus increases the incidence of abnormal and retarded embryos in superovulated heifers.
Article
Lactating cows (n = 64) were assigned randomly to shade or no shade treatments for a continuous trial (20 wk) during summer of 1976. Respirations/min and rectal temperatures were higher for no shade cows. Dry matter forage intake was 9.7% higher for shade cows, whereas water intake was 19% greater for no shade cows. Milk yield and conception rates were higher for shade managed cows. Mean plasma corticoid concentrations were high throughout the entire estrous cycle in no shade compared to shade cows (13.04 > 8.72 ng/ml). No shade cows had higher progesterone and LH concentrations, and a lower estradiol to progesterone ratio during the cycle. Results indicated that endocrine changes were indicative of recurring estrous cycles in thermal stressed lactating dairy cows. However, alterations in water intake and thermoregulation of stressed cows were associated with decreased fertility and milk production, and changes in steroid concentrations that may reduce uterine blood flow.
An update on cow cooling methods in the West
  • Armstrong
Low-cost efficient cooling method for dairy cows and its effects when used pre- and postpartum
  • Berman
Circulatory adaptations to heat stress and their relationship to fertility
  • Lublin