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High-milking sheep have a lower ovulation rate and tend to yield fewer embryos in response to superovulation and intrauterine artificial insemination
Abstract
Contents
Antagonistic relationship between milk yield and reproduction is reported in several livestock species. This study aimed to investigate whether genetic merit for milk production in dairy sheep affects responses to superovulation, embryo yield and quality. A total of 21 cross‐bred Sarda x Lacaune ewes homogeneous for age, parity and stage of lactation were included. The ewes were stratified as high‐producing or low‐producing based on their genetic merit for milk production estimated by a pentatrait repeatability animal model. Oestrus was synchronized using an intravaginal progesterone pessary inserted on Day 0 and removed on Day 14. Superovulatory treatment consisted of 350 I.U. of porcine FSH administered in eight decreasing intramuscular doses every 12 hr with a total dose of 10 ml of solution starting 12 days after insertion of sponges. Laparoscopic artificial insemination ( AI ) was performed 48 hr after pessary removal. Surgical embryo recovery was performed at Day 8 after pessary removal. Correlation between breeding value for milk production and the number of corpora lutea ( CL ) was significantly different from zero (−0.49). High‐producing ewes had a lower number of CL than low‐producing counterparts (7.6 ± 2.50 vs 12.1 ± 5.16 respectively; p < .02). Furthermore, there was a tendency for high‐producing ewes to yield fewer embryos than low‐producing females (5.3 ± 3.46 vs 9.18 ± 5.11; p = .09). No differences were observed between ewes in both genetic groups with regard to the number of embryos of grades 1, 2 and 3. To our knowledge, this is the first report highlighting an antagonism between genetic merit for milk production and the ability to produce embryos in sheep. These results deserve to be considered in sheep breeding programmes.
Supplementary resource (1)
Data
May 2017
... *Unfertilized oocyte. (Alvarez et al., 2014;Cordeiro et al., 2003;Figueira et al., 2020;Forcada et al., 2011;Lima et al., 2015;Maciel et al., 2019;Mayorga et al., 2011;Menchaca, Vilariño, Pinczak, et al., 2009;Merai et al., 2017;Taira et al., 2022). As mentioned above, this difference may be due to the influence of the intrafollicular hormone mechanism. ...
The aim of this study was to determine the effect of exogenous melatonin administration on transferable embryos by increasing total antioxidant status before superovulation in Assaf ewes. Selected ewes were randomly divided into two equal groups: melatonin ( n = 9) and control ( n = 9). In the melatonin group, a melatonin implant (18 mg melatonin, Regulin®, Ceva, Turkey) was placed under the skin of the ear 7 days prior to insertion of the progesterone‐containing sponge. In the control group, a physiological saline solution was injected under the skin of the ear on the same day. The same superovulation protocol was used in both groups. In addition, blood samples for determination of Glutathione peroxidase, superoxide dismutase, total antioxidant status and total oxidant status concentrations were collected on five different days, including the day of melatonin implant placement (Day−7), vaginal sponge insertion (Day 0), vaginal sponge removal (Day 11), mating (Day 12–13) and uterine flushing (Day 19). Embryos were collected by laparotomy on the 7th day after mating. Uterine flushing taken into petri dishes were scanned under a stereomicroscope, and the quality and developmental stages of the embryos were recorded. In the study, total corpus luteum count and total cell count were found to be higher in the control group than in the melatonin group ( p < .05). When the results were evaluated in terms of oxidative stress index, a negative correlation was found between the total number of corpus luteum, number of cells obtained, count of transferable embryos and number of Grade 1 embryos on Day 0. There was also a positive correlation oxidative stress index and the number of unfertilized oocytes on Day−7. As a result, exogenous melatonin administration prior to superovulation during the breeding season is thought to have a negative effect on embryo yield and quality. Therefore, the use of exogenous melatonin in MOET studies during the breeding season is recommended to be investigated in new studies.
... Thus, it is nec es sary for sheep to be sub mit ted to MOET pro grams when they are in lac ta tion and dur ing the non-re pro duc tive sea son. When this approach is em ployed, the first as pect that de serves at ten tion is that there seems to be an im pair ment of the su per ovu la tory re sponse in an i mals of high milk po ten tial [46]. In ewes, the 17β-estra diol me tab o lism increases due to el e vated feed in take [47]. ...
This study assessed the effect of progestogen treatment length on ovarian parameters and embryo yield in superovulated Lacaune ewes collected by nonsurgical embryo recovery. Twenty-three lactating ewes were superovulated 30 d apart using a cross-over design. All ewes received 60 mg of MAP intravaginal sponges for 6 (G-6 group) or 9 (G-9 group) d. A total dose of 133 mg pFSH was given in six decreasing doses (twice a day) starting at 60 h before device removal. Ultrasound examination of the ovaries was performed at the first pFSH injection and one day before embryo recovery, which was performed 6–7 d after the onset of estrus. Embryo recovery was conducted only in ewes that expressed estrus and were mated. There was no difference (P > 0.05) in the total number of follicles between G-6 (15.7 ± 1.0) and G-9 (15.6 ± 0.8) at the time of the first pFSH treatment. The percentage of responding donors with ≥3 corpora lutea (CL; 78.2% [18/23] vs 69.5% [16/23]), mean (±SEM) CL number (7.0 ± 1.2 vs 8.1 ± 1.6), transcervical passage rate (94.4% [17/18] vs 83.3% [15/18], and ova/embryo recovery rate (54.5% [60/110] vs 68.0% [83/122]) were not different (P > 0.05) between the G-6 and G-9 groups. However, the mean number of viable embryos was lower (P < 0.05) in the G-6 group (1.8 ± 0.7) than in the G-9 group. (3.5 ± 1.1). In conclusion, treatment with an intravaginal MAP sponge for 9 d during a superovulation protocol is beneficial for viable embryo yield in Lacaune ewes out of the breeding season.
Abstract In this paper, we present recent advances in the molecular dissection of complex traits in dairy sheep and discuss their possible impact on breeding schemes. In the first step, we review the literature data on genetic polymorphisms and the effects of sheep αs1-casein and β-lactoglobulin loci. It is concluded that the results are rather inconsistent and cannot be used in dairy sheep selection. In a second step, we describe the strategy implemented in France, Italy and Spain taking advantage of the genetic maps for QTL detection. These studies were part of a European project, called "genesheepsafety", which investigated both milk production and functional traits. Preliminary QTL results are presented for production traits.
The relationship between milk production in donor cows (74) and quality of embryos was examined in the experiment. According to their milk production, the donors were divided into three groups. In the group 1 there were 18 donors with the milk yield lower than 5000 kg per lactation; in group 2, 32 donors, with milk yield between 5000 kg and 7000 kg, and in group 3, 24 donors with milk production over 7000 kg. Number of total embryos and percentage of transferable embryos in groups were statistically significant. The higher rate of non-transferable embryos was recorded in donors in group 3 with high milk production (48.91%). A positive correlation was recorded between the number of total embryos suitable for transfer decreased in cows with higher milk production (r =-0.267), and an important correlation was recorded (r = -0.070) between milk production and transferable embryo number.
La lapine peut être fécondée aussitôt après la mise bas ou tout au long de la lactation, et être simultanément gravide et allaitante. Néanmoins, la réceptivité des femelles est variable au cours de la lactation : elle est maximale aussitôt après la mise bas (proche de 100 %) et minimale 3-5 jours après (40-65 %). Bien que les résultats expérimentaux concernant les effets de la lactation sur le taux d’ovulation et la mortalité embryonnaire soient parfois contradictoires, la fertilité et la prolificité des lapines allaitantes sont globalement plus faibles que celles des lapines non allaitantes. En effet, la lactation a, d’une manière générale, un effet négatif sur le pourcentage de femelles ovulant (-26 %), le taux de gestation (-33 %), et la viabilité foetale (-10 %). De plus, la lactation entraîne une diminution de la croissance pondérale des foetus (-20 %). L’hyperprolactinémie et la faible progestéronémie chez les lapines simultanément gravides et allaitantes, ainsi que le déficit nutritionnel engendré par la production laitière, semblent être les principaux facteurs responsables des effets observés.
Heritabilities and correlations for milk yield (MY), fat yield (FY), protein yield (PY), combined fat and protein yield (FPY), fat percentage (F%), protein percentage (P%), age at first kidding (AFK), interval between the first and second kidding (KI), and real and functional productive life at 72 mo (FPL72) of 33,725 US dairy goats, were estimated using animal models. Productive life was defined as the total days in production until 72 mo of age (PL72) for goats having the opportunity to express the trait. Functional productive life was obtained by correcting PL72 for MY, FY, PY, and final type score (FS). Six selection indexes were used, including or excluding PL72, with 6 groups of different economic weights, to estimate the responses to selection considering MY, FY, PY, and PL72 as selection criteria. The main criteria that determined the culling of a goat from the herd were low FS, MY, and FY per lactation. Heritability estimates were 0.22, 0.17, 0.37, 0.37, 0.38, 0.39, 0.54, 0.64, 0.09, and 0.16 for PL72, FPL72, MY, FY, PY, FPY, F%, P%, KI, and AFK, respectively. Most genetic correlations between the evaluated traits and PL72 or FPL72 were positive, except for F% (−0.04 and −0.06, respectively), P% (−0.002 and −0.03, respectively), and AFK (−0.03 and −0.01, respectively). The highest genetic correlations were between FPL72 and MY (0.39) and between PL72 and MY (0.33). Most phenotypic correlations between the traits evaluated and FPL72 and PL72 were positive (>0.23 and >0.26, respectively), except for F% (−0.004 and −0.02, respectively), P% (−0.05 and −0.02), KI (−0.01 and −0.07), and AFK (−0.08 and −0.08). The direct selection for PL72 increased it by 102.28 d per generation. The use of MY, FY, PY, KI, or AFK as selection criteria increased PL72 by 39.21, 27.33, 35.90, −8.28, or 2.77 d per generation, respectively. The inclusion of PL72 as selection criterion increased the expected response per generation from 0.15 to 17.35% in all selection indices studied.
This study aimed to investigate monthly changes in oestrus and ovulatory activity of Sicilo-Sarde sheep. Experimental animals comprised 25 adult and 10 maiden ewes at the start of the experiment. For 12 consecutive months (September-August), the females were exposed to natural photoperiod and permanently kept in presence of seven aproned rams. Oestrus was checked daily and ovarian activity was monitored by monthly endoscopies during the last week of each month. Ovulation rate for a particular month was assessed as the sum of corpora lutea or corpora albicans present on both ovaries at the time of endoscopy. Proportions of ewes observed in oestrus at least once a month were lowest in March (24.3%) and highest in June and October (100%). They tended (p < 0.06) to be different according to age, dropping during summer from a common value of 100% in June to 85.7% and 90% in July and then to 57.1% and 70% in August for, respectively, the Adults and Maiden females. Overall, the experimental period, 92.5% and 83.8% of Adult and Maiden ewes ovulated at least once per month (p < 0.01) respectively. Least proportions ovulating, attained 60% and 30% in April for, respectively, Adult and Maiden ewes before peaking up at 100% again in May (p < 0.05). Mean (±SD) ovulation rate of Sicilo-Sarde sheep is 1.40 ± 0.503. Adult females had a higher (p < 0.001) ovulation rate than Maiden sheep with respective average values of 1.51 ± 0.516 and 1.16 ± 0.373. It varied little between months and decreased in Adults from a maximum value of 1.95 in October to a minimum value of 1.16 in April. It is concluded that benchmarking seasonal variations of reproductive activity in Sicilo-Sarde breed would be valuable in designing improved management calendars for this breed.
This study investigated the factors affecting milk production and lactation curve parameters from the complete lactations of Awassi dairy sheep. The animals were kept in a single flock under intensive management and milked twice daily starting at lambing. Lambs were removed from the ewes at birth into an artificial rearing unit. The results of the analyses of 3740 complete lactations showed a mean litter size of 1·28 lambs born per ewe lambing and average total milk yield of 506 l from lactations 214 days in length and with an average lambing interval of 330 days. Mean lactation number was 3·71 and ewes conceived on average in the 6th month of the lactation. The lactations peaked on day 45 at a yield of 3·44 l. The maximum milk secretion potential of the ewes was 3·9 l/day, with milk yield increasing at 62 g/day mid way between lambing and peak yield and declining at 16·5 g/day mid way between peak and the end of lactation. Age at first lambing, lactation number, litter size, month of lambing and month of conception during the lactation had significant effects ( P< 0·05) on some or all of the lactation parameters investigated. Relatively high milk yield was obtained in lactations starting in the January to March period. The monthly effect on milk production was explained by significant ( P< 0·05) heat load and photoperiod effects. High milk production was found to have a significant (P< 0·05) adverse effect on reproductive performance. Conceptionfollowed a significant (
P< 0·05) short term variation in milk production.
Artificial inseminations (n = 678 168) recorded during 5 years in five French artificial insemination (AI) centres (2 'Lacaune', 1 'Manech tête rousse', 1 'Manech tête noire' and 1 'Basco béarnaise') were analysed to determine environmental and genetic factors affecting the insemination results. Analyses within centre-breed were performed using a linear model, which jointly estimates male and female fertility. This model combined four categories of data: the environmental effects related to the female, those related to the male, the non-sex-specific effects and finally the pedigree data of these males and females. After selection, the environmental female effects considered were age, synchronisation (0/1) on the previous year, total number of synchronisations during the female reproductive life, time interval between previous lambing and insemination, already dry or still lactating (0/1) when inseminated, and milk quantity produced during the previous year expressed as quartiles intra herd * year. The environmental male effects were motility and concentration of the semen. The non-sex-specific effects were the inseminator, the interaction herd * year nested within the inseminator, considered as random effects and the interaction year * season considered as a fixed effect. The main variation factors of AI success were relative to non-sex-specific effects and to female effects. Heritability estimates varied from 0.001 to 0.005 for male fertility and from 0.040 to 0.078 for female fertility. Repeatability estimates varied from 0.007 to 0.015 for male fertility and from 0.104 to 0.136 for female fertility. These parameters indicate that genetic improvement of AI results through a classical polygenic selection would be difficult. Moreover, in spite of the large quantity of variation factors fitted by the joint model, a very large residual variance remained unexplained.
Multiple ovulation and embryo transfer (MOET) is a very important tool for the genetic improvement and preservation of endangered livestock. However, the success of a MOET programme highly depends on the number of transferable embryos in response to a superovulation treatment. Thus, the aim of this study was to compare the number and quality of embryos produced during natural oestrus under porcine FSH treatment without the use of progesterone devices to more traditional protocols. Forty Sarda sheep were divided into 2 groups: without sponges (WS) (n = 20) and with sponges (S) containing 40mg FGA for 12 d (n = 20) (control group); 350 I.U. of porcine FSH per sheep was administered in eight decreasing doses twice daily starting four days after estrus was detected (Day 0) in group WS and 48 h before sponge removal in group S. A single i.m. dose of 125 μg of cloprostenol was administered on Day 6 after estrus in group WS to induce luteolysis. Sheep were naturally mated 24 h after cloprostenol injection or sponge removal. Seven days after mating, an inguinal laparotomy was performed and the number of corpora lutea (CL) recorded. Embryos were recovered surgically by flushing each uterine horn. A total of 38 fresh and 22 vitrified embryos were transferred in pairs into 3 groups of recipients seven days after estrus detection: fresh embryos from group S (S-F) (n = 9), fresh embryos from group WS (WS-F) (n = 10) and vitrified embryos from group WS (WS-V) (n = 11). Data on the number of corpora lutea (CL), recovered ova and embryos (OER), and quality 1-2 and 3 embryos (EQ(1-2), EQ(3)) per ewe were analyzed by ANOVA. Recovery (RR), fertility (FR) and quality 1-2 embryo (Q(1-2)R) rates per treatment were analyzed by a Chi Square analysis. A Chi Square analysis was also applied to pregnancy rate (PR), lambing rate (LR) and twinning rate (TR) of fresh and vitrified embryos in order to analyze embryo transfer results. Among all superovulation variables analysed, results show statistically significant differences in mean number of CL/ ewe (9.3 ± 3.9 vs 7 ± 3.2), RR (67% vs 80 %) and FR (100% vs 80%) (P < 0.05) between WS and S groups respectively. There were no significant differences in PR (78%, 70% and 82%), LR (67%, 60% and 59%) and TR (71%, 71% and 44.4%) among S-F, WS-F and WS-V groups respectively. In conclusion, it is possible to produce a good number of transferable embryos during natural oestrus avoiding the use of sponges.
First-parity 305-d milk yield and intervals between first and second kiddings from 1975 through 2005 were analyzed to estimate genetic and environmental parameters for United States Alpine, LaMancha, Nubian, Saanen, and Toggenburg dairy goats. The data set included 43,612 does with first-parity milk yield and 25,863 does with first kidding interval. Parameters were estimated by REML using bivariate mixed models within and across breeds. Fixed effects were month and herd-year of kidding within breed and month and breed-herd-year of kidding across breeds. Random effects were animal and residual. The heritability estimate for first-parity milk yield was 0.36+/-0.01 across breeds and ranged from 0.35 to 0.38 within breed; heritability for first kidding interval was 0.05+/-0.01 across breeds and ranged from 0.00 to 0.15 within breed. The estimate of the genetic correlation between first-parity milk yield and first kidding interval was positive (unfavorable) across breeds (0.35+/-0.09). Estimates of environmental correlations within and across breeds were positive (0.16-0.25). The presence of unfavorable genetic relationships between milk yield and kidding interval indicates a need to include reproductive performance as a selection criterion.
In the non breeding period, the effect of two superovulatory treatments (eCG/FSH in single dose or FSH alone in four decreasing doses) on the production of embryo quality following in vitro viability after vitrification procedures was investigated using forty-four adult Sarda breed ewes. In sheep treated with eCG/FSH, the mean number of corpora lutea was significantly (P < 0.05) higher (11.8+/-4.0 vs. 8.05+/-3.8), although the recovery rate was significantly (P < 0.01) lower (74.6 vs. 59.9) than with FSH alone. After vitrification (ethylene glycol and glycerol) was repeated three times, the rates of re-expansion at first and second warming were significantly (P < 0.01) higher in embryos derived from FSH alone than in those with both gonadotrophins (94.9 and 41.9 vs. 72.8 and 18.6) and after the last vitrification the hatched blastocyst rates were 22.5 and 7.6. After differential stain, blastocysts derived from FSH alone showed a mean number of cells significantly higher than blastocysts from eCG/FSH (184.2 vs. 157.7). It was concluded that superovulatory treatment with eCG/FSH may increase the ovarian responses compared with FSH alone, but these embryos showed a reduction in viability rates after repeated vitrification.
Poor fertility has become a major reason for involuntary culling of dairy cows in the United Kingdom. Calving interval (CI) and body condition score (BCS) are recorded, heritable, genetically correlated with each other, and could be used to extend the scope of dairy indices to include fertility traits. The use of U.K. insemination information for the evaluation of fertility has not been examined previously. Fertility and correlated traits were examined using nationally recorded milk (MILK = daily milk yield at test nearest d 110), BSC, and fertility traits (CI and the insemination traits of nonreturn rate after 56 d, NR56; days to first service, DFS; and number of inseminations per conception, INS). Genetic parameters for the traits were estimated simultaneously with a multitrait sire maternal grandsire (MGS) model and a multitrait BLUP sire MGS model was used to predict sire predicted transmitting abilities for each trait. The relationship between the fertility traits and other predicted transmitting abilities calculated in the United Kingdom was then examined. Heritabilities for the fertility traits were CI = 0.033 +/- 0.01, DFS = 0.037 +/- 0.01, NR56 = 0.018 +/- 0.001, and INS = 0.020 +/- 0.001, with a genetic correlation of 0.671 +/- 0.063 between CI and DFS and -0.939 +/- 0.031 between NR56 and INS. There was an unfavorable genetic correlation between the fertility traits and milk yield and BCS. Predicted transmitting abilities produced are similar in size and range to those produced in other studies and genetic trends are as expected. Results to date are encouraging and suggest that the planned program of work will lead to a fertility index that, when used by breeding companies, will lead to improvements in national dairy cow fertility.
The Assaf breed of dairy sheep, a stabilized cross of the Awassi and East Friesian breeds, has replaced the Awassi as the breed of choice in its country of origin, Israel, and has spread to other Mediterranean countries. In Israel the Assaf breed is managed under an intensive production system involving weaning lambs at birth, rearing them artificially, and milking ewes after parturition. There are several breeding periods in the year when ewes are mated following hormonally synchronized estrus. Records of 18,976 lactations from 5 farms were analyzed to investigate factors that influenced Assaf milk and reproductive performance. Lactation curves were fitted to each lactation, and a range of parameters and calculated values were analyzed. Daily milk yield records also were analyzed to describe a typical Assaf lactation and compared with those of the Awassi breed. Factors affecting age at first lambing also were studied. An average Assaf ewe kept under this intensive management regimen was found to produce 334 L of milk during a 173-d lactation. Mean litter size was 1.57 lambs/ewe lambing, and lambing interval was 272 d. Milk production was affected by litter size, with twin- and triplet-bearing ewes producing approximately 20 L more milk per lactation than single-bearing ewes. Day length was the major environmental variable influencing milk yield. The difference between midsummer and midwinter day lengths accounted for a difference in daily milk yield of 0.44 L in favor of summer. Ewe lambs that were mated for the first time at later ages produced more lambs and more milk due to greater early lactation characteristics. Milk production was found to be negatively associated with subsequent reproductive performance. Comparing these results with those from an earlier study in the Awassi breed, the Assaf was found to produce less milk during a shorter lactation than the Awassi, but its greater litter size made it a more profitable breed.
In this paper, we present recent advances in the molecular dissection of complex traits in dairy sheep and discuss their possible impact on breeding schemes. In the first step, we review the literature data on genetic polymorphisms and the effects of sheep alphas1-casein and beta-lactoglobulin loci. It is concluded that the results are rather inconsistent and cannot be used in dairy sheep selection. In a second step, we describe the strategy implemented in France, Italy and Spain taking advantage of the genetic maps for QTL detection. These studies were part of a European project, called "genesheepsafety", which investigated both milk production and functional traits. Preliminary QTL results are presented for production traits.
The relationship between milk production in donor cows and the yield and quality of embryos and oocytes was examined. No significant differences in the yield of embryos among cows with low (group 1), medium (group 2), and high milk production (Group 3) were found. In group 1, there was the higher number of embryos per one donor. A significantly higher percentage of transferable embryos were recorded in the cows in group 1 with low milk production in comparison with group 3 with high milk yield (P<0.01). A slightly negative correlation (r = -0.35) was recorded, i.e. the number of embryos suitable for transfer decreased in cows with higher milk production. Also, a significant higher frequency of occurrence of degenerated embryos was recorded in the donors in group 3 with high milk production (P<0.01) in comparison with the other two groups, while the number of degenerated embryos increased positively in correlation to donors with higher milk production (r = 0.58). No differences emerged in the percentage of yielded oocytes among the groups.
The reproductive performance of young adult rams (age 13 or 14 months) of the Dorset, Finnish Landrace (Finn), Suffolk and Scottish Blackface (Blackface) breeds was evaluated over 14 months, beginning in June (latitude 50°N). Blood FSH, LH and testosterone signals were examined in relation to testicular function as rams passed through their second sexual cycle. Consistent with estrual activity of ewes at this latitude, the testes were relatively large and testosterone concentrations higher for longer durations in the Dorset and Finn rams. Increases in FSH concentration in the summer were soon followed by increases in testicular size in all four breeds, but only in the Finns and Suffolks did changes in FSH and scrotal circumference continue to parallel each other throughout the year. Basal (interpulse) LH was associated with LH pulse frequency (r ≥ 0.64, P < 0.01) in the four breeds and was, on average, five-fold higher (∼1ng/ml) when the testes were developed than regressed. Whereas the relationship between changes in testosterone and LH pulse frequency throughout the testicular cycle was highly significant in each breed (r ≥ 0.63, P < 0.01), such a relationship with basal LH was observed only in the Blackface rams (r = 0.74). Regression of the testes was aligned with decreases in testosterone, but not with numbers of sperm voided in urine. Other than in the Finns, changes in sperm output resembled those in testosterone 60 days earlier, especially in the Suffolks and Blackface (r ≥ 0.73, P < 0.01). Results indicate that FSH secretion per se can play a central role in regulating the magnitude of the testicular cycle in both seasonal and relatively nonseasonal breeds, while participation of basal LH in regulating testosterone secretion and of testosterone in regulating sperm output (spermatogonial proliferation) may be more important in the seasonal breeds. Normal breed differences were noted in adult body weight, testicular size (e.g. smaller in the Blackface) and sexual behavior (e.g. more intense for the Finn). Scottish Blackface rams, a rare breed in Canada, adapted well to the severe prairie climate.
The management of an experimental flock of dairy sheep was changed from a onceyearly to a frequent-lambing regime. Results are reported on the performance of the flock under the new regime in the course of 3 years. There were 53 and 160, 46 and 242, and 70 and 237 Awassi and Assaf (East-Friesian x Awassi) ewes, respectively, in the flock at the beginning of the 3 consecutive years. A breeding calendar was adopted to produce four mating seasons each year, namely June–July; September–October; December–January; March–April.
Average annual production was 1·16 ± 0·24 lambs and 209±9 kg milk for Awassi ewes, and 2·07 ± 0·20 lambs and 287 ± 19 kg milk for Assaf ewes. Hoggets of the same breeds produced 0·61 ± 0·14 and 1·23 ± 0·10 lambs and 99 ± 37 and 220 ± 21 kg of milk, respectively.
Following the February-March lambing, conception rates of hormone-treated ewes weaned 2 or 70 days post-partum were 57·1 and 48·8% respectively ( P < 0·10). There were no differences in the length of the post-partum interval to conception between low and high milk-yielding ewes. Fertility was highest in the September–October and December–January mating periods, intermediate in June–July and lowest in March–April.
Twenty-seven per cent of the original 126 mature Assaf ewes and 15% of the original 46 mature Awassis remained in the flock at the end of 3 years for further breeding. Thirty-one per cent of the mature Assaf population (mixed ages) and 21% of the hoggets were culled in the course of 3 years due to failure to conceive within 6 months post-partum . With Awassi ewes the rate of failure was much higher.
Ewes which had lambed twice and completed, on average, 1·5 lactations in a year, produced 30% more milk per year than those which lambed only once during the same period. The more frequent lambing resulted in shorter lactations (156 days) and lower average daily milk yields (1·27 kg) compared with the 182 days and 1·41 kg in the less frequently lambing groups. Pregnancy during early stages of lactation had a small but significant (P < 0·05) effect on the concurrent lactation. Shortening the breeding interval had a much more marked effect on the subsequent lactation. Ewes that conceived, on average, 120 days post-partum , in the subsequent lactations produced 17% more milk than those conceiving 60 days post-partum ( P < 0·02).
Ewes gaining weight at a rate of 5–7 kg during the first 2 months of pregnancy produced, on average, 0·27 kg less milk per day than those which either lost or maintained their weight in that period (P < 0·01).
Fourteen adult ewes from each of three breeds, Karagouniko (K), Serres (S) and Chios (C), were maintained, barren, as a single flock at Diavata (latitude 40·5°N) for 2 years. Oestrus was checked twice daily by vasectomized rams for 17 months from April 1979. For K, S and C ewes, respectively, the mean dates of onset were 7 August (s.e. 6·5), 31 July (s.e. 8·2) and 28 July (s.e. 7·3) (P < 0-05) and the spread of first oestrus extended to 100, 94 and 95 days, respectively. Over all breeds, the dates of first oestrus ranged from 23 May to 19 September. Mean dates of last oestrus were 16 April (s.e. 8·5), 5 April (s.e. 9·5) and 20 May (s.e. 7·0) (P > 0·01) and the mean durations of the breeding period were 253 (s.e. 11·0), 247 (s.e. 12·2) and 301 (s.e. 10·2) days, respectively (P > 0·01). In the second season, the mean dates of first oestrus were 4 September (s.e. 2·4), 28 August (s.e. 5·1) and 25 July (s.e. 6·2), respectively (P < 0·01).
There have been a number of reports on the frozen storage of ram semen, and artificial insemination with frozen semen has been performed on an experimental basis in several countries. Intensive laboratory studies led to considerable progress regarding the freezing and thawing procedures (Salamon & Visser, 1972; Colas, 1975). However, fertility following insemination tends to be considerably lower than for fresh or chilled semen (Maxwell et al. 1980).(Received April 22 1983)
Post-partum interval to oestrus and conception was studied in relation to previous and current lactation (milk yield and lactation length), age of ewe and treatment with intravaginal sponges in a total of 186 Awassi ewes lambing in December/January. In the first trial, 62% of ewes, tested for oestrus twice a day with vasectomized rams until the end of May, showed oestrus between 1 and 170 days after lambing with a mean interval of 83 (s.d. 31·9) days. Neither current nor previous lactation had important effects on the rebreeding interval (P > 0·05). In another trial where ewes were exposed continuously to fertile rams until the end of March, 50% showed oestrus with a mean interval of 56 (s.d. 23·7) days (range 33 to 113 days). Of those showing oestrus, 86% conceived with a mean post-partum interval of 70 (s.d. 33·0) days (range 33 to 133 days). Lactation yield had no significant effect on the lambing-to-oestrus interval (P > 0·05) but ewes with longer lactations showed longer lambing-to-conception intervals (P > 0·01). Treatment with progesterone-impregnated vaginal sponges at 1, 2 and 3 months post partum showed an increase in the percentage of ewes showing oestrus from 35% to 75% and in those conceiving from 25% to 70% as the timing of treatment increased from 1 to 3 months post partum. It is concluded that lambing three times in 2 years is biologically feasible and that hormone treatment can facilitate its operation in practice.
Functional traits have become important for efficient breeding schemes in the dairy goat and sheep industries, mainly in Mediter-ranean countries, due to increased costs of production relative to milk prices and consumers demand for safe, quality food and attention to animal welfare. The challenge facing the European dairy sheep and goat sector is to cost-effectively produce typical cheeses attractive to the consumer, i.e. of high quality and perceived to be safe, while maintaining production in less favoured rural regions. The emphasis for functional traits related to udder morphology and health, at the moment on a quantitative genetics basis, has resulted from the knowledge established during the last decade that selection on milk traits only, as practiced for several decades for breeds benefiting from efficient breeding schemes, would lead in the long term to "baggy" udders that are more difficult to milk by machine and more susceptible to mastitis. At the same time another window has been opened based on new molecular tools allowing the detection and mapping of genes of economic importance in farm animals. To date, marker-or gene-assisted selection (MAS/GAS) has been applied in dairy small ruminants either for introgression of a major gene such as the Booroola mutation or for selection of major genes such as the polled mutation and s1-casein gene in goats, or the PrP gene for scrapie resistance in sheep. These applications clearly showed the need for balance over time between selection for polygenes and the major gene for a given trait, or between increasing frequency of favorable alleles of a major gene while maintaining selection for other traits and the genetic variability within the breed. It showed that the selection for major genes will be more profitable at the breed level if an efficient breeding scheme is already running to be able to account for these optimizations over time. Moreover attention is also turning to the mapping of quantitative trait loci (QTL) for production and functional traits. Results are promising since numerous QTL have now been detected, mainly in dairy sheep, showing that cattle results can be partly transferred to dairy small ruminants. But QTL fine mapping is a crucial next step before any application of MAS/GAS because of the need to dramatically reduce genotyping costs for these species. Finally, given the large differences among existing breeding programmes for dairy sheep and goats, the ability to use these new technologies and molecular knowledge in the breeding schemes will probably be breed dependent at least in a near future.
Dairy sheep have been farmed traditionally in the Mediterranean basin in southern Europe, central Europe, eastern Europe, and in Near East countries. Currently, dairy sheep farming systems vary from extensive to intensive according to the economic relevance of the production chain and the specific environment and breed. Modern breeding programs were conceived in the 1960s. The most efficient selection scheme for local dairy sheep breeds is based on pyramidal management of the population with the breeders of nucleus flocks at the top, where pedigree and official milk recording, artificial insemination, controlled natural mating, and breeding value estimation are carried out to generate genetic progress. The genetic progress is then transferred to the commercial flocks through artificial insemination or natural-mating rams. Increasing milk yield is still the most profitable breeding objective for several breeds. Almost all milk is used for cheese production and, consequently, milk content traits are very important. Moreover, other traits are gaining interest for selection: machine milking ability and udder morphology, resistance to diseases (mastitis, internal parasites, scrapie), and traits related to the nutritional value of milk (fatty acid composition). Current breeding programs based on the traditional quantitative approach have achieved appreciable genetic gains for milk yield. In many cases, further selection goals such as milk composition, udder morphology, somatic cell count, and scrapie resistance have been implemented. However, the possibility of including other traits of selective interest is limited by high recording costs. Also, the organizational effort needed to apply the traditional quantitative approach limits the diffusion of current selection programs outside the European Mediterranean area. In this context, the application of selection schemes assisted by molecular information, to improve either traditional dairy traits or traits costly to record, seems to be attractive in dairy sheep. At the moment, the most effective strategy seems to be the strengthening of research projects aimed at finding causal mutations along the genes affecting traits of economic importance. However, genome-wide selection seems to be unfeasible in most dairy sheep breeds.
The aim was to study the polymorphisms of the melatonin receptor 1A gene (MTNR1A) and its relationship with seasonal reproduction in the Sarda sheep breed. Four-thousand multiparous ewes reared under natural photoperiod were randomly chosen. Genomic DNA was extracted and subjected to PCR for the amplification of the main part of exon II of the ovine MTNR1A gene (GenBank U14109). PCR products were subjected to restriction enzymes MnlI and RsaI and placed into +/+, +/- or -/- group for MnlI and C/C, C/T or T/T group for RsaI. Samples were cloned and sequenced. The sequences were aligned with the U14109 sequence of GenBank. Data were subjected to allelic frequency analysis and to the chi(2) test in order to evaluate the link between genotype and reproductive activity. After MnlI digestion, allelic frequency was 0.78 for allele +and 0.22 for allele -; genotype frequency of the +/+ homozygote was 68%, 20.5% for +/- and 11.5% for -/-. After RsaI, allelic frequency was 0.66 for allele C and 0.34 for allele T; genotype frequency of the C/C homozygote was 53.5%, 26% for C/T and 20.5% for T/T. The population was in Hardy-Weinberg disequilibrium both for the MnlI and RsaI. Lambing frequency of +/+ genotype ewes was higher in the period September-December while for -/- genotype in January-April (P<0.01). Lambing of C/C genotype ewes showed a higher frequency in September-December while for T/T genotype in January-April (P<0.01). Results confirmed that the polymorphism of the MTNR1A locus was also present in the Sarda with a higher incidence of the +/+ and C/C genotypes. The animals that carried one of these two gene isoforms showed a not seasonal reproductive activity with the lambing period in September-December.
ExtractSheep ova are normally obtained from the reproductive tract using the flushing techniques described by Hunter et al.(1955). Oviduct flushes, in the writers' experience, give a higher recovery of ova than uterine flushes, but they result in more adhesions of the tract, which can cause infertility. Consequently, the development of satisfactory uterine flushing techniques appears necessary before ova can be recovered repeatedly from superior ewes. This paper describes such a technique.
Repeated superovulation using three treatments of pFSH at intervals of 45 to 55 days during the same breeding season was carried out in 18 Préalpes ewes. The embryos were recovered by surgery after the first two treatments and by slaughter after the last one at Day 6. Three lots of control ewes (n = 5 or 6) receiving the same superovulation treatment were slaughtered respectively at the same time. The first and third repeated superovulation treatments gave averages of 5.2 +/- 0.6 and 4.5 +/- 0.6 corpora lutea. The second one gave 3.4 +/- 0.4 corpora lutea, which was significantly lower than with treatments 1 and 3, but adhesions did not permit a perfect view of the whole surface of the ovaries. Recovery rates decreased regularly with repeated collection (88.2, 52 and 24%, respectively). The proportion of embryos at the morula/blastocyst stage also decreased from 86 and 93% to 6.7% at the third treatment. The development of post-surgical lesions probably caused variations in the apparent rate of ovulation and a decrease of egg recovery and fertilization rates. In control ewes the mean level of superovulation did not vary significantly during the breeding season and embryonic development was normal when checked at slaughter. Repeated superovulation using pFSH is worthwhile only if the eggs are recovered by perfusion with an appropriate catheter (introduced into the uterus by laparoscopy) instead of by surgery.
The dairy industry in the United States has changed dramatically in the last decade. Milk production per cow has increased steadily because of a combination of improved management, better nutrition, and intense genetic selection. Dairy farms are larger, and nearly 30% of the dairy cows in the United States are on farms with 500 or more cows. The shift toward more productive cows and larger herds is associated with a decrease in reproductive efficiency. Cows with the greatest milk production have the highest incidence of infertility, but epidemiological studies suggest that, in addition to milk production, other factors are probably decreasing reproductive efficiency in our dairy herds. The reproductive physiology of dairy cows has changed over the past 50 yr, and physiological adaptations to high milk production may explain part of the reproductive decline. Critical areas for new research include control of the estrous cycle, metabolic effects of lactation on reproduction, mechanisms linking disease to reproduction, and early embryonic mortality. Solving reproductive loss in dairy cows will not be easy because only a small number of research groups study reproduction in postpartum dairy cows. Therefore, the present research base will need to be expanded. For this to occur, research funding must be increased above its current level and a renewed emphasis must be placed on solving the emerging crisis of infertility in dairy cows.
This review presents an overview of the technical bases of in vivo and in vitro embryo production in sheep and goat. The current limitations of in vivo production, such as variability of response to the hormonal treatment, fertilization failure in females showing a high ovulatory response, and the importance of premature regressed CL in the goat, are described along with possibilities for improvement. The new prospects offered by in vitro embryo production, by repeated ovum pick-up from live females and by juvenile breeding, are presented along with their limiting steps and research priorities. The recent improvements of embryo production and freezing technologies could be used for constitution of flocks without risks of disease transmission and will allow wider propagation of valuable genes in small ruminants populations in the future.
Bivariate models (censored linear-linear and censored threshold-linear) were used to estimate genetic parameters for production and fertility traits in the Spanish Holstein population. Records on 71,217 lactations from 41,515 cows were used: 30 and 36% of lactations were censored for days open (DO) and number of inseminations to conception (INS), respectively. Heritability estimates for production traits (milk, fat, protein) ranged between 0.18 and 0.25. Heritability of days to first service (DFS) and DO was 0.05; heritability of INS on the liability scale was 0.04. Genetic correlations between fertility traits were 0.41, 0.71, and 0.87 for DFS-INS, DO-INS, and DO-DFS, respectively. Days open had a larger genetic correlation (ranging from 0.63 to 0.76) with production traits than did DFS (0.47 to 0.59) or INS (0.16 to 0.23). Greater antagonism between production and DO may be due to voluntary management decisions for high-yielding cows, resulting in longer lactation lengths. Inseminations to conception appeared to be less correlated with milk production than were the other 2 female fertility traits. Including INS in a total merit index would be expected to increase genetic gain in terms of profit, but profit would decrease if either DO or DO and DFS were included in the index. Thus, INS is the trait to be preferred when selecting for female fertility. The genetic correlation between actual milk yield and 305-d standardized milk yield was 0.96 in the present study, suggesting that some reranking of sires could occur. Because the target of attaining a 12-mo calving interval, as implied by a 305-d standardized lactation length, is changing in the dairy industry, routine genetic evaluation of actual total lactation milk yield should be considered.
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