Weaning stress in lambs

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Sheep are subjected to a multitude of psychological and environmental stressors that cause decreased productivity, increased disease and hence to poorer welfare. The weaning is one of the most stressful procedures for all lambs not only in terms of the dam-lamb relationship, but also because of its potential effect on the health of lamb. In numerous studies have been discussed the effects of different weaning strategies, along with physiological and behavioural responses to weaning stress of lambs. However, there does not seem to be a consensus on the strategy that completely eliminates weaning stress. Sheep producers should know weaning strategies which minimize negative stress caused by nutritional, environmental, physical and social changes experienced by lambs at weaning time. The purpose of this paper is to provide an overview of the literature examining what is known about the importance and impact of weaning stress in lambs.
Journal of International Scientific Publications: Agriculture and Food
Volume 2, ISSN 1314-8591 (Online), Published at: http://www.scientific-publications.net
Ferda Karakuş
Yuzuncu Yıl University, Faculty of Agriculture, Department of Animal Science, Van, Turkey
Sheep are subjected to a multitude of psychological and environmental stressors that cause decreased
productivity, increased disease and hence to poorer welfare. The weaning is one of the most stressful procedures
for all lambs not only in terms of the dam-lamb relationship, but also because of its potential effect on the health
of lamb. In numerous studies have been discussed the effects of different weaning strategies, along with
physiological and behavioural responses to weaning stress of lambs. However, there does not seem to be a
consensus on the strategy that completely eliminates weaning stress. Sheep producers should know weaning
strategies which minimize negative stress caused by nutritional, environmental, physical and social changes
experienced by lambs at weaning time. The purpose of this paper is to provide an overview of the literature
examining what is known about the importance and impact of weaning stress in lambs.
Key words: Weaning, stress, welfare, lamb
Animal stress is identified as a unique event that elicits a specific behavioral, physiological, neuroendocrine,
endocrine, and/or immune response that may be as unique as the stressful event itself (Carroll & Burdick
Sanchez 2013). The detrimental effects caused by stress can reduce the fitness of an animal, affect reproductive
and immune systems as well as the quality of animal products and can even cause death (Etim et al. 2013).
All living organisms maintain a complex dynamic equilibrium or homeostasis, which is constantly challenged by
internal or external adverse effects, termed stressors. Stress occurs when homeostasis is threatened or perceived
to be so (Chrousos 2009). Stressor is defined as the environmental stimulus that provokes the stress response
(Kelley 1980). Sheep are subjected to a multitude of psychological and environmental stressors that cause
decreased productivity, increased disease and hence to poorer welfare. Routine management procedures such as
isolation (Altın et al. 2012), restraint (Rivalland et al. 2007), milking (Negrao & Marnet 2003), shearing (Fidan
et al. 2009), castration and tail docking (Mears & Brown 1997), and transportation (Ekiz et al. 2012a) have been
reported to be stressful to sheep.
The weaning is one of the most stressful procedures for all lambs not only in terms of the dam-lamb relationship,
but also because of its potential effect on the health of lamb. The lambs may have difficulty in adapting to the
weaning, because the weaning produces weaning shock in the lambs. The level of shock manifested by reduction
in post-weaning growth rate may vary depending on weaning age and weight, the intake of solid feed before
weaning as well as health status of the lamb. The purpose of this paper is to provide an overview of the literature
examining what is known about the importance and impact of weaning stress in lambs.
Under natural conditions, the survival of the newborn depends on the establishment of a strong and lasting social
bond with the dam. The mother-young bond has been defined as a preferential mutual, emotional attachment, of
relatively long duration (Enriquez et al. 2011). Suckling is a major factor in the strength of the mother-young
bond that usually begins at birth (Schichowski, Moors & Gauly 2008). Lambs are allowed to suck their dams
until four weeks old. At the same time good quality roughage and a concentrate mixture in pelleted form with
clean drinking water should be available in front of lambs from the second week. After the fourth week restricted
suckling should be applied to encourage the consumption of solid feed. Increasing solid feed consumption
stimulates rumen morphological development.
The sheep is a follower species and in the first day of life the ewe remains within one meter of the lamb. When
both are grazing the distance between ewe and lamb increases rapidly over the next 10 days of life, reaching a
plateau with an average distance of 20 meters (Blackshaw 2003). Schichowski, Moors & Gauly (2008) reported
that the intervals between suckling increase with age, indicating that 16 wk old lambs are more accustomed to a
Journal of International Scientific Publications: Agriculture and Food
Volume 2, ISSN 1314-8591 (Online), Published at: http://www.scientific-publications.net
separation from the mother than younger lambs. With age the distance between mother and young becomes
longer. Older lambs also move more frequently and further from the ewe than younger lambs and they do not
vocalize as much as younger ones. The fact that younger lambs were more stressed by weaning procedures when
compared with older lambs may be due to the stronger mother-young bond (Schichowski, Moors & Gauly 2008).
Accidental separation in the first few days causes great agitation of both lamb and ewe, and reunion
is immediately followed by suckling (Blackshaw 2003).
The frequency and duration of suckling decrease with reduced milk production. Therefore, progressive natural
weaning has very little apparent negative consequences on social groups of ewes and lambs (Schichowski,
Moors & Gauly 2008). A decrease in milk production leads to the distancing of both partners. The changes in the
lamb’s nutritional requirement also seem to play a part in the inception of the weaning process (Orgeur et al.
1998). Lambs reared with their mothers become accustomed to solid feed more rapidly than artificially reared
lambs (Napolitano et al. 2003). The lambs subjected to a gradual separation from their mothers exhibited a more
rapid approach to and a higher intake of solid feed than did the lambs that were abruptly removed from their
dam’s 24-30 h post-partum (Sevi et al. 2003).
The weaning is defined as the complete physical separation of mother and young, and also the transition from
feeding of milk to solid feeds. In sheep production the traditional method of weaning referred to as abrupt
separation is performed by separating lambs from their dams without applying any treatment before weaning.
The weaning age of lambs may vary between 4-16 weeks. It is recommended that lambs should not be weaned
until they reach 3-4 times of their birth weights or 12-13 kg live weight.
Ewe condition, feed quality and quantity, and target market as well as the age and weight of lamb are important
factors in determining the weaning time. Rauw et al. (2007) reported that the phenotypic correlation between
weaning weight and weaning age in lambs was positive (0.20) and highly significant (P<0.001). On the other
hand Mousa et al. (2013) estimated phenotypic and genetic correlation between birth weight and weaning weight
(eight weeks age) as 0.52 and 0.37, respectively.
Weaning weight is an important factor of influence on later growing rate and should be considered as important
criteria for lamb weaning determination. After weaning, it was expected that lambs weaning with lower weights
would have less growth rate by the effect of weaning stress and poor quality of the native pasture. Body weight is
more important than weaning age on lamb growth and it should be considered on weaning decision (Selaive-
Villarroel, Maciel & de Oliveira 2008).
Early weaning may be defined as the withdrawal of the milk supply before the time when weaning would
normally occur. The success of early weaning must depend partly upon the speed with which the rumen develop
in lambs and partly upon the level of milk production of the dams (Abou Ward et al. 2008). In many milk
production systems, lambs are separated from the ewe at an early age in order to increase the amount of milk
available for cheese making. However, this rearing system is often associated with poor performance of lambs
(Napolitano et al. 1995). Therefore, feeds given to lambs must be carefully formulated to ensure animal health.
The reaction of the animal to stressors depends on the duration and intensity of the stressors, the animal’s
previous experience to the stressors, the physiological status and immediate environmental restraints. An animal
may react either by physiological or a behavioural responses, but most often a combination of both (Etim et al.
During the weaning process, the lambs like piglets (Campbell, Crenshaw & Polo 2013) and calves (Enriquez et
al. 2011) experience changes in their physical and social environments. Therefore, weaning can be a multi-
factorial stressor, in which, nutritional, social, physical, and psychological stress are combined. Physical and
nutritional stressors are often present through the introduction and adaptation to a new diet and new
environment, whereas, psychological stress is present in the form of maternal separation and social disruption
(Earley & McGee 2011).
A potential indicator of animal welfare is the absence of stress. A multitude of hormones (e.g., ACTH,
glucocorticoids, catecholamines, prolactin, etc.) is involved in the stress response (Möstl & Palme 2002). These
hormones serve to adapt animals to stress by altering their cardiovascular, energy-producing and immune
systems (Mears & Brown 1997). There is no single biochemical assay system to measure stress. Thus, there is a
need for additional biochemical or endocrine parameters for detection of disturbances (Möstl & Palme 2002).
Journal of International Scientific Publications: Agriculture and Food
Volume 2, ISSN 1314-8591 (Online), Published at: http://www.scientific-publications.net
The evaluation parameters are not always the same for short or long periods of stress and require the use
different measures. In case of short-term stimuli, the behavioral, physiological and endocrine evaluation
parameters consist of vocalizations, escape attempts, heart rate, respiration rate, cortisol blood level, etc.
Differently, in the event of long-term stress, important behavioral, physiological and endocrine parameters can
be the reproductive efficiency, growth rate, stereotype manifestation, blood hormones and metabolites
concentrations, and immune responses (Carzedda 2011-2012).
In domestic livestock, excessive concentrations of cortisol have been linked to reduced rates of reproduction,
suboptimal growth, suppressed milk production, and suppression of immune function that could increase
susceptibility to disease (Carroll & Burdick Sanchez 2013). Plasma cortisol levels are elevated after either
physical or psychological stress. Likewise, sheep respond with elevated plasma ß-endorphin following stressful
procedures. In Suffolk lambs weaned at 7-wk old, plasma cortisol was elevated for only the first 60 min and at
24 h after weaning compared to basal levels at 0 min, while weaning did not affect plasma ß-endorphin.
Weaning had no influence on cortisol level at 48 and 72 h after weaning (Mears & Brown 1997).
Orgeur et al. (1998), who studied the consequences on animal welfare of two weaning procedures, progressive
weaning and sudden weaning, found out that the cortisol levels in ewes were not affected by separation from
their young whatever weaning method was used. In a subsequent study, Orgeur et al. (1999) evaluated the
psychobiological consequences of two types of sudden weaning at 3 months of age in sheep. Ewes and their
lambs were either completely denied the opportunity to communicate (total separation) or allowed to visually
and vocally communicate (partial separation). Plasma cortisol levels of lambs showed a greater increase when
the partners were totally separated than when maintained visual and auditory contact. Napolitano et al. (2003)
observed a lower cortisol response in ewe-reared animals than in artificially reared lambs. Ekiz et al. (2012b)
also reported that suckling management at 45-d and 75-d resulted in stress responses in lambs with increasing
plasma cortisol concentration.
The process of separation at weaning can induce some stress for lambs (Gauly et al. 2004). Early separation from
the ewe affects humoral immune response and post-separation performance of lambs as a possible consequence
of a reduced ability of young animals to cope with emotional and nutritional stresses (Napolitano et al. 1995).
Weaning performed by breeders is sometimes associated with a complete separation of the two partners.
Therefore, such practices may cause more profound behavioural and/or physiological disturbances (Orgeur et al.
1999). Lambs were generally found to be disturbed when they were separated from their mothers than when they
were reunited (Abdul-Rahman, Chikpah & Yaro 2012).
In a review on minimizing the stress of weaning of beef calves, Enriquez et al. (2011) noted that among the
many behavioural changes taken as indicators of weaning stress, the most characteristic was the high frequency
of vocalizations emitted by the calf. Vocalizations by the young are thought to evoke maternal care and the need
to reunite with the dam. Both ewes and lambs temporarily separated from each other express their distress by an
increase in bleating and locomotor activity. These behavioural modifications help the animals to cope with the
stress-inducing situation and to keep contact (Orgeur et al. 1998). Mears and Brown (1997) also concluded that
lambs separated from their mothers vocalize to show their displeasure. Orgeur et al. (1999) revealed that
regardless of the separation procedure, lambs vocalized significantly more than mothers on the day of weaning.
However, on the days after weaning, mothers were more vocal than their young. According to the researches,
this suggests either a better adaptation by the lambs to weaning or that ewes called their lambs to be suckled.
Lambs prevented from suckling their mothers and receiving milk from a bucket show more distress bleats and
less time near their companions compared with dam-suckled lambs (Napolitano et al. 2003). Schichowski,
Moors & Gauly (2008) compared lambs weaned at 8 or 16 weeks of age in two stages to those weaned by abrupt
separation. Weaning was done by one of two procedures. The traditional weaning method was by abrupt visual
and acoustical separation of the ewe and lamb. In the 2-stage method, lambs were first prevented from nursing
their dam for 1 week before their physical separation. Researchers concluded that lambs weaned with the 2-stage
method vocalized less and showed less behaviors indicative of agitation after separation than animals weaned by
the traditional method of abrupt separation. However, Sevi et al. (2003) concluded that gradual separation from
their mothers induced behavioral, endocrine and immune disturbances in lambs. The lambs subjected to a sudden
separation from their mothers displayed responses comparable to those of the dam-suckled lambs. In another
study, Camarillo (2011) compared the effect of gradual versus abrupt weaning strategies on lamb performance. It
was found that total vocalizations on Day 0, the day of initial weaning, were significantly higher for ewe and
lambs in gradual-weaned group than those from abrupt-weaned group. On day 1, mean vocalization scores were
significantly higher for abrupt-weaned ewes and lambs, as they approached 48 hours of complete separation
from each other. By day 2, abrupt-weaned ewes had dramatically decreased their frequency of vocalization.
Journal of International Scientific Publications: Agriculture and Food
Volume 2, ISSN 1314-8591 (Online), Published at: http://www.scientific-publications.net
However, gradual-weaned ewes and lambs were vocalizing more. Vocalization and agitation levels quickly
declined for both groups after day 2 and no significant differences between groups were noted after day 2
(Camarillo 2011).
The health of lamb can be adversely affected by the new pathogens associated with exposure to changing
conditions due to weaning. Especially, abrupt weaning can increase lambs’ susceptibility to disease. Milk may
play little role in the enhancement of host resilience to infection. It was found that
suckled lambs had a greater ability to resist worm establishment (Iposu 2007). Continued suckling may have
benefits in the control of nematodes in young lambs, probably through reducing nematode larval establishment.
The major benefit of continued suckling in young lambs appears to be in the provision of nutrients which
enhance growth rate rather than resilience to nematode infection (Iposu et al. 2008).
One of the most important consequences of weaning stress in lambs is the reduction in feed intake. The reduction
in feed intake results in reduced growth rate and therefore increased susceptibility to diseases.
Growth rate can be inhibited by early weaning (21-77 days) as the animals are slow in adapting to solid food
consumption as a consequence of the physiological delay in ruminal development. Thus, in the weeks following
weaning at 45 days, weight gain can drop due to a low consumption of grass and concentrate. The effect of
weaning on growth is less marked in lambs separated from their dams at 65 days of age (Napolitano, De Rosa &
Sevi 2008). Gauly et al. (2004) noted that the lower average daily gain in lambs weaned at age of 40 days
compared with unweaned lambs might be due to weaning stress.
Numerous studies have been conducted concerning the effects of different weaning strategies on lamb
performance. Sevi et al. (2003) suggested that the lambs subjected to a gradual separation from their dams
exhibited a lower growth rate than dam-suckled lambs (P<0.01) and artificially reared lambs (P<0.05, P<0.001).
However, the higher hay and concentrate consumption was not enough to bridge the gap in growth rate between
the lambs gradually separated and the other lambs. According to the researchers, the provision ad libitum of a
milk substitute having a nutritional value comparable to ewe milk may minimize the stress associated to artificial
Ekiz et al. (2012c) investigated the effects of suckling length and rearing type on average daily gains (ADG) of
lambs at different periods of growth. A significant (P<0.05) decrease in ADG was observed in lambs of SC-45
group after weaning at 45 days and in lambs of SC-75 group after weaning at 75 days. These results indicate that
weaning might cause a decrease in ADG of lambs. With respect to ADG from birth to slaughter, lambs suckled
until slaughter age (SC-120) had higher ADG than those weaned at either 45 d (SC-45) or 75 d (SC-75)
Lambs weaned at 8 weeks had greater ADG than lambs weaned at 16 weeks of age. The availability of high-
quality concentrates may have allowed early weaned lambs to compensate for the loss of maternal milk by
increased feed intake, resulting in a greater total intake of energy. However, traditional and 2-stage weaning did
not differ regarding daily weight gains (Schichowski, Moors & Gauly 2008). Also, Abou Ward et al. (2008)
indicated that age at weaning affected (P<0.05) ADG in favor of the early weaned lambs (8 weeks) compared
with the late weaned lambs (12 weeks). Similar results were obtained by Abdel-Fattah et al. (2013).
All farmers should aim to keep all their animals within their comfort zone and also employ proper management
practices in order to minimize stressful situations and allow for greater well-being, growth, reproductive
efficiency of the animals (Etim et al. 2013). Weaning is a stressful time for lambs and their dams due to the
sudden separation from their dams and changes in the social and physical environment. Therefore, weaning time
is a crucial period in the management of ewes and lambs. In numerous studies have been discussed the effects of
different weaning strategies, along with physiological and behavioural responses to weaning stress of lambs.
However, there does not seem to be a consensus on the strategy that completely eliminates weaning stress. Sheep
producers should know the main stressors associated with weaning and benefit from appropriate strategies to
minimize the adverse effects of weaning stress in lambs. Lambs should be carefully observed in the process of
weaning due to the effect of weaning stress on post-weaning lamb performance.
Journal of International Scientific Publications: Agriculture and Food
Volume 2, ISSN 1314-8591 (Online), Published at: http://www.scientific-publications.net
The risks of pneumonia, scours, coccidia and urinary calculi are increased at the time of weaning. To avoid
additional stress, vaccinations, castration, worming and tagging should be performed at least two weeks before
weaning. Lambs should be monitored closely for health problems (Redden 2013).
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Supplementary resource

  • ... In sheep production, weaning process is recognized as one of the stressful procedures which is influenced by environment, nutrition and psychology that potentially affect the growth performance and health of the lambs [1,2]. ...
    Full-text available
    Background: Postbiotics have been established as potential feed additive to be used in monogastric such as poultry and swine to enhance health and growth performance. However, information on the postbiotics as feed additive in ruminants is very limited. The aim of this study was to elucidate the effects of supplementation of postbiotics in newly-weaned lambs on growth performance, digestibility, rumen fermentation characteristics and microbial population, blood metabolite and expression of genes related to growth and volatile fatty acid transport across the rumen epithelium. Results: Postbiotic supplementation increased weight gain, feed intake, nutrient intake and nutrient digestibility of the lambs. No effect on ruminal pH and total VFA, whereas butyrate and ruminal ammonia-N concentration were improved. The lambs fed with postbiotics had higher blood total protein, urea nitrogen and glucose. However, no difference was observed in blood triglycerides and cholesterol levels. Postbiotics increased the population of fibre degrading bacteria but decreased total protozoa and methanogens in rumen. Postbiotics increased the mRNA expression of hepatic IGF-1 and ruminal MCT-1. Conclusions: The inclusion of postbiotics from L. plantarum RG14 in newly-weaned lambs improved growth performance, nutrient intake and nutrient digestibility reflected from better rumen fermentation and microbial parameters, blood metabolites and upregulation of growth and nutrient intake genes in the post-weaning lambs.
  • ... However, natural weaning rarely occurs in a production setting and early weaning (i.e. immediate dissolution of the ewe-lamb bond prior to the natural weaning age) is performed due to several factors including, but not limited to; labor, pasture and feedstuff availability, pasture quality (Orgeur et al., 1998;Napolitano et al., 2008), and lamb weight and age (Karakuş, 2014). It is a common practice in intensive sheep operations such as those found in the Eastern United States for weaning to occur as early as 60 days of age (Ricketts, 1999;Barkley, 2014). ...
    Two experiments were conducted to determine the effects of weaning age on lamb growth and the severity of parasitic infection in grazing lambs. All lambs were fed in a feedlot until they reached a set marketable weight after their allocated grazing period. In experiment 1, 48 Hampshire. ×. Dorset and Suffolk. ×. Dorset crossbred lambs and 24 Dorset. ×. Suffolk and Dorset. ×. Hampshire crossbred ewes were placed into one of two weaning treatments for 63. days: Pasture control (PC): lambs weaned early at 60. days of age and placed on pasture and Ewe (E): Lambs placed on pasture at 60. days of age with ewe and weaned at approximately 123. days of age. The E lambs had a greater average final body weight, total ADG, and PCV value on day 63 compared to PC lambs during the grazing period (P. <. 0.05). In the feedlot, E lambs spent fewer days in the feedlot to reach market weight and had a greater overall ADG with PC lambs demonstrating a greater G:F and total DMI (P. <. 0.05). In experiment 2, a total of 72 crossbred lambs and 27 crossbred ewes were placed into one of four weaning treatments for 56. days: Pasture control (PC). Ewe (E): lambs weaned at approximately 116. days of age. Social facilitator (SF): lambs weaned at 60. days of age and placed on pasture with non-lactating, non-related ewes. Feedlot control (FC): lambs weaned at 60. days of age and placed in a research feedlot facility. Feedlot control lambs were not re-exposed to parasites after the initiation of the experiment and therefore included as an industry standard control. The E lambs demonstrated greater BW from day 42 to the end of the grazing period and FC lambs had the lowest BW from day 7 to day 28 and a greater ADG on day 56 of the grazing period (P. <. 0.05). The E and FC lambs also demonstrated a smaller difference in change in PCV values from day 28 to the end of the grazing period (P. <. 0.05). In the feedlot, E lambs required less total weight gain and had lower DMI compared to all other treatments to reach market weight (P. <. 0.05). The FC lambs had a greater total weight gain, DMI, and G:F compared to all other treatments (P. <. 0.05). The results from these two experiments demonstrate that extending the weaning age of lambs beyond 60. days of age in pasture-based systems can be beneficial from an animal health standpoint and requires less harvested grain in the feedlot to reach a market appropriate endpoint.
  • ... Variation in feed intake, protein deficiency, starvation, shortage of feeding space, vaccination and various other managemental operations may lead to stress which ultimately cause immunosuppression [6,7]. Stress cause of reduction in performance and increase susceptibility to disease [8]. Therefore it is mandatory to minimize the stress and restore the immunity in livestock for optimum production by adopting proper managemental practice and or supplementation of immunomodulators. ...
  • Article
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    We investigate the effects of postbiotic Lactobacillus plantarum RG14 on gastrointestinal histology, haematology, mucosal IgA concentration, microbial population and mRNA expression related to intestinal mucosal immunity and barrier function. Twelve newly weaned lambs were randomly allocated to two treatment groups; the control group without postbiotic supplementation and postbiotic group with supplementation of 0.9% postbiotic in the diet over a 60-day trial. The improvement of rumen papillae height and width were observed in lambs fed with postbiotics. In contrast, no difference was shown in villi height of duodenum, jejunum and ileum between the two groups. Lambs received postbiotics had a lower concentration of IgA in jejunum but no difference in IgA concentration in serum and mucosal of the rumen, duodenum and ileum. In respect of haematology, postbiotics lowered leukocyte, lymphocyte, basophil, neutrophil and platelets, no significant differences in eosinophil. The increase in of IL-6 mRNA and decrease of IL-1β, IL-10, TNF mRNA were observed in the jejunum of lambs receiving postbiotics. Postbiotics also improved the integrity of the intestinal barrier by the upregulation of TJP-1, CLDN-1 and CLDN-4 mRNA. Postbiotic supplementation derived from L. plantarum RG14 in post-weaning lambs enhance the ruminal papillae growth, immune status and gastrointestinal health.
  • Article
    Plasma cortisol, β-endorphin, T3 and T4 were determined in lambs before, during and after exposure to stress in order to evaluate the potential use of these hormones to objectively measure stress responses. Lambs were exposed to tail-docking, castration, weaning, isolation, and restraint stress. Twelve ewe and 24 ram lambs were assigned to the experiment, with 12 of the ram lambs surgically castrated when 3-wk old. Tail docking within 24 h of birth did not (P > 0.05) elevate either plasma cortisol or β-endorphin. Castration markedly elevated (P < 0.001) plasma cortisol and β-endorphin within 15 min of surgery. Both hormones were highly elevated for the first 4 h . Plasma cortisol returned to control levels by 24 h whereas β-endorphin was still elevated (P < 0.05) 24 h after castration. Plasma cortisol levels were elevated for the first 60 min following weaning (P < 0.005) and again at 24 h after dam removal (P < 0.001). Plasma β-endorphin was not elevated (P > 0.05) any time during the 72 h following weaning. Plasma cortisol (P < 0.001) and β-endorphin (P < 0.05) were elevated during the first 60 min following the start of 1 h of isolation. Results were similar for partial and total isolation. No effects of isolation were found for the next 23 h. Plasma cortisol (P < 0.005) was elevated during the first 30 min following 4 min of shearing-like restraint, whereas plasma β-endorphin was elevated only at 7 min (P < 0.05) after restraint began. No further effects of restraint were found prior to termination of sample collection at 24 h. None of the stressors employed affected plasma concentrations of T3 and T4. This study has shown that measurements of plasma cortisol and β-endorphin in blood samples obtained before, during and after stress are useful in assessing stress in lambs. The painful stressor, castration, induced marked and prolonged elevations of both hormones, whereas psychological stressors elicited graded, short-term cortisol responses and limited β-endorphin responses.
  • Article
    The aim of the experiment was to compare the welfare and weight gains of artificially reared lambs when gradually separated from their mothers or separated from them early and immediately or gradually moved from maternal to reconstituted milk. Forty Comisana lambs were assigned to a control dam-suckled (DS) group and three test groups of 10 each. The lambs in the GRAD group were gradually separated from their dams reducing the time spent with the mothers by degrees over 10 days, while the lambs in the substitute (SUB) and EM groups were abruptly removed from their dams 24–30h post-partum. After separation, the lambs in the SUB group were provided with a milk substitute, while the lambs in the EM group were subjected to a gradual transition from ewe milk to the milk substitute over 10 days. At 12 and 32 days of age all the lambs underwent open-filed tests, during which their behavioral responses to isolation and to an inanimate stimulus—a hobby horse—were measured. In addition, blood samples were collected immediately before the isolation test, and then 10 and 60min after to evaluate cortisol concentrations. Cell-mediated immune responses in vivo to phytohemagglutinin (PHA) injection were evaluated at 7, 21 and 35 days of age, while antibody titers against chicken egg albumin (OVA) were determined at 2, 10, 20, 30 and 42 days of age. The weight gains of the lambs were also recorded weekly. When isolated in a novel environment, the GRAD lambs performed less frequent climbing attempts (P
  • Article
    Weaning sheep under farming conditions combines two factors that can be potentially stressful agents: (1) physical separation of mother and young and (2) modification of lambs' feeding habits. The purpose of this study is to measure the consequences on animal welfare of two weaning procedures currently used in France: (1) progressive weaning (PROG) with daily separation starting when lambs are 3.5 weeks of age increasing in duration until definitive weaning at 3 months and (2) sudden weaning (SUDD) at 3 months. Forty Ile de France ewes and their 60 lambs were used in the study. In the PROG group, a sharp increase in the vocal activity of ewes and lambs was recorded during periods of temporary separation. However, animals became accustomed to the procedure with repeated separations and very few behavioural reactions were recorded when lambs were definitively weaned at 3 months of age. In the SUDD group, ewes and lambs were very vocal at weaning but signs of disturbance were no longer noticeable after two days. In ewes, the cortisol levels were not affected by separation from their young whatever weaning method was used, but an increase in leucocyte levels was recorded in SUDD ewes on the day of weaning. In lambs the number of coccidial oocysts excreted at 9.5 and 16.5 weeks of age was higher in PROG than in SUDD lambs. Their growth rate was not affected by the daily separation. In conclusion, neither method seems highly stressful in sheep. However, lambs are more sensitive to parasite infestation when separation from the mother is repeated until weaning. Finally, sudden weaning, which involves less work for the breeder, can be used without heavy disadvantages on welfare.
  • Article
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    The influence of artificial rearing at different ages was evaluated in Comisana lambs. Animals were assigned to three test groups (2d, 15d and 28d) on the basis of age (2, 15 or 28 days, respectively) at the time of their separation from the ewe, and three corresponding control non-separated groups (2c, 15c and 28c). On the day of separation from their dam, animals were injected i.m. with 250 μg of keyhole limpet hemocyanin in complete Freund's adjuvant. Antibody titers and surface leukocyte antigens were determined at weekly intervals. Group 2d showed a lower antibody response than the corresponding control group (F = 8.0, P < 0.01), whereas groups 15d and 28d did not differ from the control. No significant difference between test and control groups was found in the proportion of cells bearing different surface antigens. Furthermore, lambs were subjected to a behavioral test (isolation from tactile and visual contact with other animals). Younger animals showed reduced duration of movement (162.8 vs. 272.1 and 221.1 s for 2d, 15d and 28d, respectively; U = 21.0, P < 0.01 and U = 30.5,P < 0.05, respectively; Mann-Whitney U test) and enhanced latency time (15.8 vs. 3.4 and 2.3 s for 2d, 15d and 28d, respectively; U = 28.0, P < 0.01 and U = 14.5, P < 0.001, respectively; Mann-WhitneyU test) in comparison with older animals. Cortisol concentration was evaluated immediately before the separation from the mother and 15, 45, 90, 150, and 225 min after. An increased cortisol level was observed in group 2d 15 min after removal from the dam (LSD: P < 0.001), whereas the other two groups did not show any significant increase. In addition, during the first 28 days of age all the animals were weighed at birth and at weekly intervals. When the animals were removed from the mother either at 2 or 15 days of age, the daily weight gain decreased significantly in comparison with the corresponding control groups (107.1 vs. 157.1 g for 2d and 2c, respectively, F = 4.8, P < 0.05; 37.3 vs. 126.8 g for 15d and 15c, respectively, F = 5.8, P < 0.05). In conclusion, early separation from the ewe affects humoral immune response and post-separation performance of lambs as a possible consequence of a reduced ability of young animals to cope with emotional and nutritional stresses.
  • Article
    Soon after parturition a lasting and mutual ewe–lamb bond is established. However, in an increasing number of intensive sheep farms, lambs are separated from the dam at an early age. When artificial rearing is applied lambs are often kept with mothers for 2 days to allow the ingestion of maternal colostrum and then abruptly removed from their dams. Thus, lambs experience a marked emotional stress represented by the loss of the most relevant social model at this early stage of their behavioural development and a nutritional stress represented by the transition from maternal milk to a commercial milk substitute. These animals when exposed to open field tests show reduced levels of vocalization, are slower to initiate movements, spend less time in ambulatory behaviour and display an increased cortisol response than non-separated animals. In addition, artificial rearing performed on lambs from 2 days of age onward can cause decreased cellular and humoral immune responses. The main oral abnormal behaviour performed by artificially reared lambs is represented by sucking the navel or the scrotum of pen mates. This activity is evident from the initial days on reconstituted milk and lasts until weaning from milk. Attempts have been made to reduce the detrimental effects of early separation. Some of them mainly focus on the emotional aspects (it is recommended not to leave a lamb alone for artificial rearing), others aim at reducing the nutritional impact of artificial rearing (milk intake can be increased by offering a mix of ewe milk and a milk replacer during the first week and then gradually moved to a diet based only on milk substitute which results in higher growth rates). As compared with artificial rearing, early weaning performed at 3 months of age is associated with a later disruption of the mother–young bond and the consequent direct replacement of maternal milk by solid food. However, when they are given the chance, ewes and their lambs form long-term social associations which exceed the age of natural weaning, regarded as the end of the milk feeding period. Early weaned lambs emit an increased number of high pitched bleats immediately after weaning than before and this increment is still evident 2 days afterwards. Neither partial nor gradual separation from mothers is able to reduce the stress associated with early weaning. In conclusion, premature separation from mothers has clear and marked detrimental effects on various functions in lambs. For lambs maternal deprivation seems to be worse at 2 days (artificial rearing) than at 3 months of age (early weaning)
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    The Rafter 7 Merino flock was initiated in Nevada in 1990 with the purchase of 500 purebred Rambouillet ewes. A gradeup program was initiated using Australian Merino genetics with the aim of developing a purebred Merino flock. Early in the project the Rafter 7 Merino line was created, which is approximately 5/8 Merino and 3/8 Rambouillet and has been a closed line since 1999. In a genetic selection program that includes weaning weight, weights must be adjusted for environmental factors. The present study investigated factors influencing weaning weight in 9,594 lambs. Results show a decrease in lamb weaning weights with the inclusion of Merino blood in the lines. At weaning, rams were heavier than ewes (P < 0.001) and weights decreased with increased litter size (P < 0.001). Lambs born from 2-yr old dams had lower weaning weights than lambs born from older dams (P < 0.01), and lambs born from 5-year old dams had lower weaning weights than lambs born from 3-year old dams (P < 0.05). Lambs born from 3-, 4-, 6-, and 7-year old dams did not significantly differ. Multiplicative-adjustment factors for adjusting lamb weaning weights to a common sex, age of dam, and birth-rearing type were compared with values from the Report of the National Sheep Improvement Program Technical Committee. Adjustment factors were slightly lower for triplet ewes and rams born from a 3- to 6-yr old dam. Other adjustment factors were very similar, suggesting that adjustment factors derived from more intensive production systems are applicable to our extensive production systems as well.
  • Article
    The experiment was conducted to verify whether the first machine milkings post-partum cause stress in primiparous ewes, and to study the profile of cortisol (CORT), adrenalin (AD), noradrenalin (NOR), oxytocin (OT) and milk parameters during the first milkings. Twelve Lacaune ewes milked twice daily were used in this experiment. Milk yield and milk composition were determined during the first 15 days of lactation. Blood samples were taken before, during and after the morning milking on days 1, 4, 7 and 15. Baseline levels of AD, NOR and OT did not change significantly during the successive milkings. However, basal levels of CORT varied between days and the highest level was observed before the first machine milking. From days 1 to 4, there was no significant release of OT, however on days 7 and 15, the onset of milking induced a significant and abrupt increase in OT levels. In contrast, AD and NOR measured on day 1 were higher than on day 15. On days 1 and 7, CORT release was greater than on day 4, but CORT release observed on days 1 and 7 did not differ from that on day 15. OT released during machine milking was significantly associated with milk yield, milk fat and milk protein, however total CORT release was negatively associated with milk yield. At the same time, three ewes never released OT during milkings. These ewes produced significantly less milk (660±140ml/day) than other ewes (1386±115ml/day), and two of these three ewes presented high AD and NOR levels. In the present research, milk yield, OT, AD and NOR levels suggest that the first milkings are important stressors, however the majority of the ewes had adapted to machine milking by day 15.
  • Article
    Full-text available
    The aim of this research were to study the effect of weaning age and weight on post-growing rate (PWG) and to estimate the optimal weaning age (WA) and weight (WW) of Morada Nova-white variety breed lambs raised under extensive system conditions. A total of 31 male and female lambs were evaluated, being 19 lambs born in April/May 2001 and 12 lambs born in February/March 2002. Lambs were distributed in the following treatments at weaning: 1) weaning age = T1: weaned at 60 days; T2: weaned at 75 days; T3: weaned at 90 days, and 2) weaning weight = T1: weaned with 9 to 10.4kg weigth; T2: weaned with 10.5 to 12.4kg weight and T3: weaned with above 12.5kg weight. The PWG was recorded through successive weightings done every fourteen days from weaning to 180 days of age. Data were analysed through a statistical model that included age and weight at weaning, sex and year of birth as fixed effects. Lambs weaned with 60, 75 and 90 days of age showed non-significant differences (P>0.05) on PWG. However, WW had a significant influence (P<0.05) on lamb weight. The group weaned with 9-10.4kg had smaller live weight than those weaned with 10.5-12.4kg or above 12.5kg. No differences were found between these last two groups. Also, sex had significant effect (P<0.05) on lamb growing with males being heavier than females (20.7kg and 17.6kg, respectively). Year of birth did not affect PWG. It was concluded that weight at weaning is more important than age at weaning on post-weaning growing of lambs. The most efficient live weaning weight on white Morada Nova lambs raised in extensive system production is over 10.5kg.
  • Article
    Environmental stressors are involved in the etiology of important livestock diseases, including transmissible gastroenteritis in young pigs, Newcastle's and Marek's disease in chickens and shipping fever in cattle. Unfortunately, very little research has been conducted to learn how stress alters host resistance, although it is generally assumed that the immune system of the host is affected. This paper identifies eight stressors that typically occur in modern livestock production units: heat, cold, crowding, mixing, weaning, limit-feeding, noise and restraint. All of these stressors have been shown to alter the immune system of animals. These changes in immune function may ultimately explain the physiological basis of disease-environment interactions. A thorough understanding of stress-induced changes in host resistance will also provide the scientific basis for effective prophylactic therapy. More controlled experiments are needed to learn how stress alters the susceptibility of animals to infectious and noninfectious diseases.