Behavioural development in the neonatal lamb: effect of maternal and birth-related factors

The survival of the neonate relies on the integrated expression of appropriate behaviours from both the mother and young. In precocious species, like the sheep, the speed with which the lamb stands and seeks the udder is related to lamb survival. In this study the effects of birth difficulty, lamb birth weight, ewe loss or gain in backfat from conception to delivery, ewe parity, litter size, and lamb sex on neonatal lamb behavioural development were investigated in over 500 lambs of two breeds (Scottish Blackface and Suffolk). Lambs that required assistance to be delivered were significantly slower to perform all neonatal behaviours than unassisted lambs (P<0.001), and were less active over the first 3 days after delivery (P<0.05). There were no effects of lamb birthweight that were not accounted for by the increased likelihood of requiring assistance in heavier birth weight lambs. Ewes that mobilised less body fat during their pregnancy produced lambs that stood and sucked quickly (P<0.001), and were more active over the first 3 days of life. Lambs born to first parity ewes were slower to stand and suck than lambs born to experienced ewes (P<0.001). There was an improvement in time taken by lambs to stand, seek the udder and to suck with each increase in ewe parity. Litter size had an additional retarding influence on the behaviour of multiple-born lambs that could not be accounted for by birthweight. In the Suffolk breed male lambs were slower to stand and suck than female lambs, this effect was not seen in Blackface lambs. These data demonstrate that lambs that require assistance at birth, even if they survive the birth process, lambs born to ewes that lose a lot of condition over pregnancy or first parity ewes, triplet lambs and, at least in some breeds, male lambs are slower to progress through the sequence of neonatal behaviours. These lambs are, therefore, at greater risk of not surviving to weaning.     

From birth to colostrum: early steps leading to lamb survival

New-born lambs have limited energy reserves and need a rapid access to colostrum to maintain homeothermy and survive. In addition to energy, colostrum provides immunoglobulins which ensure passive systemic immunity. Therefore, getting early access to the udder is essential for the neonate. The results from the literature reviewed here highlight the importance of the birth site as the location where the mutual bonding between the mother and her young takes place. Attraction to birth fluids by the periparturient ewe leads to intense licking of the lamb. Grooming not only dries, cleans and stimulates the newborn it also facilitates bonding through learning of its individual odour. Ewes having twins should ideally stay on the birth site for at least six hours in order to establish a strong bond with both lambs and favour lambs survival. However, primiparous ewes or ewes having high levels of emotivity are more likely to exhibit poor maternal behaviour. In addition, difficult parturition and weather conditions have an indirect effect on the behaviour of the mother and are other major causes of lamb death. On the lamb's side, rapid access to the udder and early suckling are extremely important. Delayed lactation or insufficient colostrum yield may be fatal especially since suckling has strong rewarding properties in the establishment of a preference for the mother, which in turn increases lamb survival. Insufficient access to the udder in mothers leaving the birth site too soon after parturition, especially in twin-bearing ewes, could also partly account for the high incidence of loss of mother-young contact and subsequent death in such lambs. Strategies to improve neonatal survival should be aimed at maximising lamb vigour, colostrum production, and mutual mother-young bonding through adequate feeding in late pregnancy and selection on behaviour.     

Development and validation of on-farm behavioural scoring systems to assess birth assistance and lamb vigour

Lamb mortality remains a significant welfare and economic issue for sheep production. Lamb survival is to a degree dependent upon an easy delivery and the expression of appropriate behaviours from both mother and offspring, such as rapid standing, udder seeking and sucking by the lamb. Genetic solutions have the potential to improve birth assistance and lamb behaviour but large amounts of data are needed. Therefore, to achieve this objective, simple, proxy methods (scoring systems) were developed to quantify the level of birth difficulties and lamb vigour on farm. In the first study, detailed historical behavioural data from 1156 lambs (Scottish Blackface and Suffolk (S)) were analysed to develop criteria for 3 scores: birth assistance, lamb vigour and sucking assistance. The birth assistance score was developed by analysing the relationships between birth presentation and intervention levels, and intervention level and labour length. Lambs with abnormal birth positions required more assistance than normally presented lambs and lambs with long labours required more and greater assistance than those with short labours. Lamb vigour score was developed by analysing the latencies for the lamb to first perform specific behaviours; more vigorous lambs reach landmark behaviours faster than low vigour lambs. The sucking assistance score was developed from the relationship between the latency to suck successfully and assistance level, where lambs that were slow to suck required more assistance than lambs that were quick to suck. In the second study, the behaviour scoring systems (5-point categorical scales) were validated using a commercial flock of 80 twin-bearing crossbred ewes mated with either Texel (T) or S sires by simultaneously recording scores and the latency to perform specific landmark behaviours (i.e. to stand, seek the udder and suck). The vigour scores (recorded at 5 min of age) were compared with the latency from birth to standing and showed that lambs with lower (better) vigour scores were faster to stand after birth than those with higher scores. The sucking assistance scores were compared with the latency from birth to sucking, and showed that lambs with lower sucking assistance scores are quicker to suck than those with high scores. These results showed that the scoring systems could provide a practical and reliable assessment of birth assistance and lamb behaviour on farm and were sufficiently sensitive to discriminate vigour levels between lambs sired by either S or T rams.     

The impact of lambing stress on post-parturient behaviour of sheep with consequences on neonatal homeothermy and survival

During lambing the expression of an appropriate behavioural response from both the ewe and the lamb are extremely important to lamb survival. The aim of this study was to show the effect of length and difficulty of the birth process on the expression of maternal and neonatal behaviour with consequences on homeothermy and survival of the neonate lamb. Data were collected from 61 Finnish Landrace × Rahmani crossbred (second generation) primiparous ewes and their single born lambs. Based on the average length of parturition, the ewes were grouped into short birth (less than 32.5 min) and long birth (equal to or higher than 32.5 min) classes. The data recorded include maternal and neonatal behaviour, lamb body temperature over the first 3 days of life and survival rate of the neonate lamb during the first week after birth. Blood samples were also collected from the lamb, pre-suckling and at 24 and 72 h after birth. The obtained sera were assayed for thyroid hormones (T₃ and T₄) that are associated with heat production. Ewes that had prolonged and difficult births did not show competent maternal behaviour compared to mothers with short and un-complicated deliveries, as they were slower to begin grooming their lambs after birth, spent less time licking their lambs, made less low-pitched vocalizations and nosing, were more likely to show rejection behaviour (10.34 % vs 5.4 %, P < 0.05), and were more likely to move away when the lamb sought the udder in an attempt to suck (acceptance rate, 55.5 % vs 64.79 %, P < 0.05). Similarly, lambs from a prolonged and difficult birth were significantly less vigorous after birth, as they had taken more time to stand, reach the udder and to suck successfully. These lambs had lower serum concentrations of T₃ and T₄, and they also had a reduced ability to maintain body temperature after birth. This effect persisted over the first 3 days of life and was associated with higher neonatal mortality in the first week after birth (11.54 %), compared to lambs from short and non-stressful birth processes (2.86 %, P < 0.01). From the present study, it can be concluded that, prolonged deliveries with birthing difficulty were one of the main causes of death of large, single-born lambs, as these complications cause the expression of inappropriate behavioural responses from both the ewe and neonatal lamb. Thus, interventions designed to reduce the incidence of prolonged parturitions are likely to be associated with better welfare for the ewe and the lamb and consequently improved lamb homeothermy and survival.     

Factors associated with neonatal lamb mortality

Three factors were associated with lamb neonatal mortality: birthweight (P<0.003), number of lambs born per ewe (P<0.001) and lamb sex (P<0.32). Lamb birthweight had the greatest predictive power for survival during the neonatal period. The neonatal mortality rate was 14.3%. The age specific mortality for lambs one day old was 7.9% (P<0.05). Seventy-nine percent of the lambs that died, did so by the end of the fourth post-natal day. Starvation was associated with 58.3% (P < 0.05) of the lamb deaths.     

Colostrum production in ewes: a review of regulation mechanisms and of energy supply

In sheep production systems based on extensive grazing, neonatal mortality often reaches 15% to 20% of lambs born, and the mortality rate can be doubled in the case of multiple births. An important contributing factor is the nutrition of the mother because it affects the amount of colostrum available at birth. Ewes carrying multiple lambs have higher energy requirements than ewes carrying a single lamb and this problem is compounded by limitations to voluntary feed intake as the gravid uterus compresses the rumen. This combination of factors means that the nutritional requirements of the ewe carrying multiple lambs can rarely be met by the supply of pasture alone. This problem can overcome by supplementation with energy during the last week of pregnancy, a treatment that increases colostrum production and also reduces colostrum viscosity, making it easier for the neonatal lamb to suck. In addition, litter size and nutrition both accelerate the decline in concentration of circulating progesterone that, in turn, triggers the onsets of both birth and lactogenesis, and thus ensures the synchrony of these two events. Furthermore, the presence of colostrum in the gut of the lamb increases its ability to recognize its mother, and thus improves mother–young bonding. Most cereal grains that are rich in energy in the form of starch, when used as supplements in late pregnancy will increase colostrum production by 90% to 185% above control (unsupplemented) values. Variation among types of cereal grain in the response they induce may be due to differences in the amount of starch digested post-ruminally. As a percentage of grain dry matter intake, the amount of starch entering the lower digestive tract is 14% for maize, 8.5% for barley and 2% for oats. Supplements of high quality protein from legumes and oleiferous seeds can also increase colostrum production but they are less effective than cereal grains. In conclusion, short-term supplementation before parturition, particularly with energy-rich concentrates, can improve colostrum production, help meet the energy and immunological requirements for new-born lambs, and improve lamb survival.     

Factors influencing lamb survival in a high fecundity Booroola Merino x South Australian Merino flock

The effects of year of lambing, age of ewe and litter size on lamb survival and birthweight, and the effects of ewe mating weight and pregnancy wastage (ovulation rate minus litter size) on birthweight were examined in Booroola Merino x South Australian Merino ewes. Year of lambing, litter size and their interaction were significant (P<0.001) sources of variation for lamb survival. When birthweight was included as a linear and quadratic covariate for lamb survival, year of lambing and litter size and their interaction remained as statistically significant sources of variation. Year of lambing, litter size and pregnancy wastage contributed significantly (P<0.05) to variation in birthweight. Ewe liveweight at mating was not an important source of variation (P>0.05). Birthweight was significantly (P<0.05) reduced with an increase in pregnancy wastage. Improvement of birthweight of multiple birth lambs has some potential for increasing lamb survival. Other factors influencing lamb survival (year of lambing, litter size, pregnancy wastage) require further study so that strategies for reducing lamb loss in high fecundity Merino flocks can be developed.     

Maternal behaviour and lamb survival: from neuroendocrinology to practical application

Parental care promotes offspring survival and, for livestock species, this care is provided solely by the mother. Maternal behaviour in the sheep has been exceptionally well-studied compared with other species and many of the underpinning biological processes leading to the expression of maternal care are known. In this review the current state of play with regard to the biology of maternal care will be reviewed, and its application to provide practical solutions to reduce lamb mortality considered. For maternal care to be elicited at birth the ewe requires elevated circulating oestradiol in late gestation, which stimulates the expression of oxytocin receptors in both peripheral and central areas (particularly the hypothalamic and limbic areas of the brain). At birth stretching of the vaginocervical canal elicits a spinal reflex which triggers the release of oxytocin primarily from neurones within the paraventricular nucleus of the hypothalamus. Oxytocin release causes an increase in the neurotransmitters noradrenaline, acetylcholine, glutamate and γ-aminobutyric acid (GABA) in the olfactory bulb, and other brain regions important for maternal behaviour. Finally, sensory cues provided by the lamb, in particular the amniotic fluids surrounding it, lead to the expression of maternal behaviours (licking, low-pitched bleats, acceptance of the lamb at the udder and suckling). This allows the expression of the two facets of maternal behaviour in the ewe: nurturance of the young and maternal selectivity, whereby a specific olfactory memory for the ewes own lamb is formed and the expression of maternal care is restricted to this lamb. Variation in the expression of maternal care has been demonstrated in primiparous ewes compared with multiparous, in different sheep genotypes, with undernutrition, stress in pregnancy, following a difficult delivery, and may occur with variation in ewe temperament. An understanding of the importance of the timing of various events in late pregnancy and during parturition, as well as the factors that can disrupt these events, can help to design management activities to minimise risks to the successful onset of maternal behaviour. Management practices that work with the biology of the ewe will be the most successful in ensuring that maternal care is expressed, so improving the welfare of the ewe and lamb, and the profitability of the farm.     

Applications of diagnostic ultrasonography in small ruminant reproductive management

Modern portable ultrasound machines provide the veterinary clinician with an inexpensive and non-invasive method to further examine the reproductive tract of both male and female sheep on farm which should take no more than 5 min with the results available immediately. Unlike cattle, ultrasound examination of the ovaries is not undertaken because failure to cycle during the normal season is rare in sheep and there are no common ovarian conditions causing acyclicity. Accurate diagnosis of foetal number has greatly improved the nutritional management of late gestation ewes over the past 30 years. Late gestation nutritional supply in response to foetal demand greatly reduces perinatal lamb mortality by ensuring lamb birthweight and ewe colostrum accumulation. The contents of vaginal prolapse have been determined using ultrasonography which has led to an improved method for correction. A retained foetus when second stage labour is considered to have been completed, and uterine torsion, can be identified during ultrasound examination allowing timely correction. Ultrasonographic examination of palpable scrotal abnormalities can provide much useful information particularly in the diagnosis of epididymitis, orchitis and testicular atrophy.     

Effects of sire breed on ewe dystocia, lamb survival and weaned lamb output in hill sheep systems

A study was carried out on six hill farms, located in the main hill regions of Northern Ireland, over three breeding seasons to investigate the effect of sire breed on ewe dystocia, lamb survival and weaned lamb output. On each farm, groups of 26 to 40 purebred Scottish Blackface ewes (n = 3174) were crossed with Blackface, Swaledale, North Country Cheviot, Lleyn and Texel sires by natural service (year 1) and artificial insemination (years 2 and 3). Each of the mating groups was initially balanced for ewe age, live weight and condition score, and a total of 15 sires of each breed were used over the 3 years. In total, 2272 ewes were recorded at lambing, producing 3451 lambs, over the 3 years. Sire breed had a significant effect (P < 0.001) on lamb birth weight with Blackface and Swaledale the lowest and Texel the highest. The proportion of ewes with dystocia was higher with Texel sires compared with Lleyn, Swaledale and Blackface sires (P < 0.05). Ewes mated to Cheviot sires had more dystocia than those mated to Blackface and Swaledale sires (P < 0.05), while ewes mated to Lleyn sire breed had more dystocia (P < 0.05) than those mated to Blackface sire breed. Most of the incidence of dystocia was attributable to increased lamb birth weight (P < 0.001), and some to litter size (P < 0.05). Swaledale, Cheviot, Lleyn and Texel sire breeds increased the incidence of malpresentations (P < 0.05). Lamb live weight at weaning was higher with Texel- and Cheviot- and Lleyn-sired lambs compared with Blackface- and Swaledale-sired lambs (P < 0.01). The level of lamb mortality at birth was not affected by sire breed. However, lamb mortality at weaning was lower for Lleyn-sired lambs compared with the other lamb genotypes (P < 0.05). These results indicate that the use of sires from larger breeds, such as Lleyn and Texel, within the Blackface ewe flocks can increase lamb output, with no apparent detrimental effects on lamb mortality or ewe survival, but increased assistance at lambing will be required.     

Early neonatal lamb mortality: postmortem findings

An investigation of stillbirth and early neonatal lamb mortality was conducted in sheep flocks in Norway. Knowledge of actual causes of death are important to aid the interpretation of results obtained during studies assessing the risk factors for lamb mortality, and when tailoring preventive measures at the flock, ewe and individual lamb level. This paper reports on the postmortem findings in 270 liveborn lambs that died during the first 5 days after birth. The lambs were from 17 flocks in six counties. A total of 27% died within 3 h after birth, 41% within 24 h and 80% within 2 days. Most lambs (62%) were from triplet or higher order litters. In 81% of twin and larger litters, only one lamb died. The most frequently identified cause of neonatal death was infectious disease (n=97, 36%); 48% (n=47) of these died from septicaemia, 25% (n=24) from pneumonia, 22% (n=21) from gastrointestinal infections and 5% (n=5) from other infections. Escherichia coli accounted for 65% of the septicaemic cases, and were the most common causal agent obtained from all cases of infection (41%). In total, 14% of neonatal deaths resulted from infection by this bacterium. Traumatic lesions were the primary cause of death in 20% (n=53) of the lambs. A total of 46% of these died within 3 h after birth and 66% within 24 h. Severe congenital malformations were found in 10% (n=27) of the lambs, whereas starvation with no concurrent lesions was the cause of death in 6% (n=17). In 16% (n=43) of the lambs, no specific cause of death was identified, lambs from triplet and higher order litters being overrepresented among these cases. In this study, the main causes of neonatal lamb mortality were infection and traumatic lesions. Most neonatal deaths occurred shortly after birth, suggesting that events related to lambing and the immediate post-lambing period are critical for lamb survival.     

The effect of late pregnancy supplementation of ewes with vitamin E on lamb vigour

The experiment measured lamb responses to supplementation of the pregnant ewe diet with vitamin E above requirement. Crossbred ewes were mated with either Suffolk or Texel rams. Twin-bearing ewes were randomly allocated (approximately 21 months of age at allocation) to one of four treatment groups (20 ewes per group, 10 mated with Suffolk and 10 with Texel rams). Treatments imposed were 50, 100, 150 or 250 IU supplementary vitamin E per ewe per day to give a four treatment by two sire-type factorial experimental design. Ewes were fed concentrates to meet energy requirements for stage of pregnancy and hay ad libitum. Diets were introduced approximately 6 weeks before lambing. Blood samples were obtained prior to introduction of diets, 17 days after introduction of diets and within 24 h of lambing from a subset of eight ewes per treatment (32 total). Colostrum samples were obtained from 10 ewes per treatment, 12 h after birth of the first lamb. All births were observed and a lamb vigour score was assigned to each lamb 5 min after birth. At 1 and 12 h after birth, rectal temperature, and at 12 h after birth, sex, crown-rump length and BW of each lamb were recorded. Mean ewe plasma α-tocopherol concentration prior to introduction of the diets was 1.5 μg/ml (s.e.m. 0.09) and did not differ between groups. There were positive linear (P < 0.001) effects of dietary vitamin E on plasma (17 days after introduction of diets) and colostrum (12 h after birth) α-tocopherol concentrations. Lamb vigour scores were superior (P < 0.001) for lambs sired by Texel rather than Suffolk rams but there were no differences as a result of vitamin E supplementation. Lamb mortality was low and unrelated to either sire or supplementary vitamin E. Lamb birth and weaning weights were also unaffected by vitamin E supplementation. Supplementing the ewe with vitamin E therefore had no effect on any lamb measurements.     

Early post-natal behaviour in lambs of ten breeds

Activity and sucking behaviour during the first hour after birth, and rectal temperature were recorded in 297 lambs of 10 breeds: Scottish Blackface, Welsh and Cheviot (hill breeds); Oxford, Border Leicester, Southdown, Merino and Finn (lowland); Soay and Boreray Blackface (feral).Two components of behaviour were analysed; the time to stand following parturition and the time to reach the udder. There were significant breed differences in both components. Lambs stood for at least 3 min during the first hour except for about half the Leicesters and most Finns. The feral and hill breeds and the Oxfords reached the udder early; the remaining breeds were slow or unsuccessful. Failure to reach the udder was associated with a higher incidence of hypothermia, especially in Finns and Merinos.Weather (combined air temperature and windspeed) was correlated with udder-seeking success but not with the time to stand.Within breeds, birthweight affected the times to stand and reach the udder, but litter size did not, except through its effect on birthweight.The present results and other data from the same breeds showed that those breeds with effective udder-seeking behaviour also tended to have good resistance to hypothermia and low perinatal mortality.     

Comparison of the survival of fertilized eggs from adult ewes in the uteri of adult ewes and ewe lambs

Fertilized eggs, obtained from mature donor ewes, were transferred into the uteri of adult ewes and ewe lambs (1 or 2 eggs per recipient). The survival rate to term of the transferred eggs was similar in the two classes of recipients. The percentage of adult ewe and ewe lamb recipients which gave birth to twins was 45.3 and 41.1 respectively. Gestation length was shorter (P less than 0.01) and lamb birth weight lower (P less than 0.01) for ewe lamb recipients. The results indicate that the generally lower lambing rate of ewe lambs compared to adults is unlikely to be due to unfavourable uterine conditions.     

Effects of exogenous progesterone on gestation length, foetal survival and colostrum yield in ewes

Twin bearing mature ewes (n=40) were treated with exogenous progesterone (100mg daily in oil) or vehicle (oil control) from Day 143 of gestation until lambing to investigate the effects on gestation length, foetal survival and colostrum yield and composition. Compared to control ewes, progesterone treated ewes had increased (P<0.05) serum progesterone concentrations (by 4.3 ng/ml) before lambing and in the first day post-partum (by 10 ng/ml). Progesterone treatment increased gestation length (150.4+/-0.6 days versus 147.8+/-0.6 days, P<0.05) and colostrum yield at 1h after lambing (P<0.05) but the colostrum had a lower concentration of IgG (P=0.02). In the first 24h after lambing, total colostrum and IgG yields were not different between groups. Four (20%) of the progesterone treated ewes produced either one or two dead lambs, while one ewe died on day 155 without initiating the birth process. We conclude that the daily administration of 100mg progesterone resulted in extended gestation length and reduced lamb survival but did not lower colostrum yield.     

Neonatal size and infant mortality at high altitude in the western Himalaya

A prospective study was undertaken in Ladakh, India, a high-altitude region of the Himalaya, to investigate the effects of small average birth size on neonatal mortality. While such studies exist from high-altitude regions of the New World and shed light on the adaptive status of high-altitude-dwelling populations there, this is the first to examine this relationship in the Himalaya. In a sample of 168 newborns, birthweight and other anthropometric measurements were reduced relative to Andean and Tibetan newborns. Logistic regression and hazard analysis showed that neonatal biological characteristics such as weight, fatness, and circumferences were important predictors of survival probabilities of infants, especially in the neonatal period. Low Rohrer's Ponderal Index (PI) was particularly strongly related to poor survival outcome. Males and females showed no significant differences in mortality risk. Data derived from reproductive histories revealed that neonatal mortality accounted for 70–80% of total infant mortality in Ladakh. Compared to other high-altitude studies, small newborn size in Ladakh was associated with much higher mortality risks; mortality risk rose dramatically with birthweights below the mean (2,764 grams), which characterized 50% of all newborns. It is argued that newborns in Ladakh are subject to strong directional selective forces that favor higher birthweights that incur lower risks of neonatal mortality, while Andean infants are subject to relatively mild selection pressure at both ends of the birthweight distribution. Given the overall small size at birth of Ladakhi newborns and the poor survival outcomes of newborns below the mean, it is suggested that this population is less well adapted in a biological sense to the stresses inherent in this high-altitude environment than are Andean populations, perhaps due to the relatively recent colonization of the area and the substantial genetic admixture that has occurred in the past. © 1994 Wiley-Liss, Inc.     

Reproductive performance of Polwarth and Corriedale sheep in Tasmania

The reproductive performance of 27 Polwarth and 9 Corriedale flocks was studied under commercial conditions in Tasmania. Mean ovulation rate was 149% but the mean number of lambs marked per ewe joined was only 88%. The major sources of wastage contributing to the overall loss were identified as an 18% loss of embryos in twin-ovulating ewes which gave birth to only one lamb, and a mean perinatal lamb mortality of 21% of lambs born. There was no significant difference in embryo survival between unilateral and bilateral twin-ovulating ewes.     

The effect of different types of stressors during mid- and late pregnancy on lamb weight and body size at birth

Mid-pregnancy shearing has consistently been shown to increase lamb birth weight, which can lead to an increase in lamb survival rates. However, shearing ewes during the winter months and under outdoor pastoral farming conditions can expose the recently shorn ewe to a greater risk of hypothermia. The aim of this study was to determine if exposure of ewes to repeated stressors, in mid- and late pregnancy, would result in an increase in lamb birth weight. This information may assist in the elucidation of the mechanism for the birth weight response to mid-pregnancy shearing, which in turn could assist in the design of management options to increase lamb birth weight without placing the ewe at risk. One hundred and forty-four twin-bearing Romney ewes were allocated to one of six mid-pregnancy treatments: control, isolation on 2 or 10 occasions, sham-shearing on 10 occasions, intramuscular cortisol injection on 10 occasions or shearing. Isolation, sham-shearing and cortisol treatments were conducted twice a week beginning, on average, day 74 of pregnancy and shearing occurred on day 76. During pregnancy, ewe treatment had no effect on ewe live weight. However, average ewe body condition scores were higher in the shorn group than in the sham-shorn or cortisol groups (P < 0.05). Intramuscular injections of cortisol had a greater effect on ewe plasma cortisol concentrations than all other treatments (P < 0.05). Shearing produced a greater plasma cortisol response than isolation × 10 and sham-shearing (P < 0.05). Ewe plasma cortisol responses decreased during the 5 weeks of isolation and sham-shearing but cortisol injections produced a greater response during the fifth treatment than the first or ninth treatments (P < 0.05). Lambs born to shorn ewes were heavier and had a longer crown rump, forelimb and hind limb lengths than all other lambs (P < 0.05). In addition, lambs born to ewes in the cortisol treatment were lighter than lambs born to control, isolation × 2, isolation × 10 and shorn ewes (P < 0.05). The plasma cortisol concentrations observed for ewes injected with cortisol were far greater than those observed in all other groups, which is likely to explain the low birth weights of lambs born to ewes in that group. These results indicate that the mechanism by which mid-pregnancy shearing increases lamb birth weight is unlikely to be repeated stressors.     

Effects of nutritional level during late pregnancy on colostral production and blood immunoglobulin levels of Karakul ewes and their lambs

An experiment was conducted to examine the changes in colostral production and composition in Karakul ewes fed at different nutritional levels. Pregnant ewes were randomly allotted to one of four groups (n = 20 per group) 90 days after artificial insemination. Three groups were fed with total mixed rations supplying 90, 100 and 110% of the NRC requirements, respectively, and the last group served as the control feeding on natural vegetations until parturition. Blood samples were taken from the jugular vein during late pregnancy, and soon after lambing. Fifteen singleton ewes from each group were hand-milked completely at 1, 12 and 24 h post-lambing. Samples of colostrum were obtained and the lambs were fed with their ewe's colostrum (30 g/kg BW) at each milking. Blood samples were taken from the lambs before receiving their first colostrum, and again at 24 and 48 h post-lambing. Ewes on 110% NRC diet produced significantly (P < 0.01) more colostrum than did the ewes in other groups. Feeding level did not have a significant effect on the IgG level of the colostrums and blood sera of ewes and lambs. Mean IgG concentration in the ewe serum was greatest during late gestation (1–2 months before lambing) and were significantly reduced at 1 h post-lambing. Non-immunoglobulin composition of colostrum was not significantly affected by the treatment. There was a significant correlation between IgG levels of the ewe serum and colostrum (r = 0.64, P < 0.0001). Mean weight of the ewes on the control ration at lambing and the mean birth weight of their lambs were significantly lower as compared with other dietary groups. The results suggested that hand-feeding of Karakul ewes on poor rangeland vegetation with 110% NRC for 2 months before parturition increased colostral production, decreased the ewe loss and increased lamb birth weight which is beneficial to lamb survival.     

Analyses of lamb survival of Scottish Blackface sheep

Scottish Blackface lamb viability records at birth, and postnatal survival from 1 day to 14 days, from 15 days to 120 days and from 121 days to 180 days were used to determine influential factors and to estimate variance components of lamb survival traits. The binary trait viability at birth was analysed using a linear model whereas the postnatal survival traits were analysed as continuous traits using a Weibull model. The data consisted of about 15 000 survival records of lambs born from 1996 to 2005 on two farms in Scotland. The models included fixed factors that had significant effects and random direct and maternal additive genetic effects and maternal litter effects for viability at birth, and sire and maternal litter effects for the postnatal survival traits. The possible effect of maternal behaviour measured around lambing on lamb survival was investigated in separate analyses. Male lambs were found to be at a higher risk of mortality than females during all periods considered. The effect of type of birth and age of dam was more important during the preweaning period than at later ages. The postnatal hazard rate was not significantly affected by the behaviour score of the dams. The genetic merit of dams had more influence on viability at birth than the genetic merit of lambs themselves. Estimates of heritability for postnatal survival traits were in the range of 0.18 to 0.33 and were significantly greater than zero. These results indicate that lamb survival can be improved through farm management practices and genetic selection. Both animal and maternal genetic effects should be considered in breeding programmes for improving viability at birth.