Genetic correlations between reproduction of crossbred ewes and the growth and carcass performance of their progeny

Genetic correlations were estimated between first cross ewe reproduction traits and growth and carcass traits of their second cross lamb progeny. The 2460 crossbred ewes were progeny of 74 maternal breed sires and mainly Merino dams. The ewes had 3 joinings to terminal sire rams with 6824 joining records resulting in 9002 lambs born and 7176 lambs slaughtered. The ewe reproduction traits included: fertility, litter size, ewe rearing ability or lamb survival, number of lambs born (NLBj) and weaned (NLWj) per ewe joined, with traits reflecting ewe productivity being total litter weight weaned (TWWj) per ewe joined and the component trait average lamb weaning weight in the litter (AWW). The lamb growth traits included weight of the lambs at birth (BWT), weaning (WWT) and post weaning (PWWT) as well as growth rate pre and post weaning. The lamb carcass traits included hot carcass weight (HCWT), dressing yield (DRESS%), fat depth (FatGR, FatC), eye muscle depth (EMD) and area (EMA) and meat quality traits (colour and pH). The genetic correlations were estimated by bivariate mixed models using ASReml. The genetic correlations between the composite reproduction traits of the ewes and the post-weaning growth rate of their lambs were high (0.67 for NLBj and 0.65 for NLWj). There were moderate positive correlations between NLWj and WWT (0.36), PWWT (0.49) and pre weaning growth (0.36) and NLBj with PWWT (0.31). BWT was negatively correlated with litter size (−0.34) and positively with ewe rearing ability (0.38). Most of the other genetic correlations were smaller than their standard errors which generally ranged from 0.2 to 0.3. The genetic correlations for HCWT with all the ewe reproduction traits were positive and moderate (0.29–0.53) and high with the ewe productivity traits that included weight of lambs (TWWj 0.98 and AWW 0.96). The genetic correlations among the other traits were variable and had high standard errors, generally ranging from 0.1 to 0.5. However there were generally negative and unfavourable genetic correlations between the reproduction traits and DRESS% and meat colour L*, whereas those with carcass fat (FatC and FatGR) were generally negative and favourable.     

Genetic analyses of live weight and carcass composition traits in purebred Texel,Suffolk and Charollais lambs

Lamb live weight is one of the key drivers of profitability on sheep farms. Previous studies in Ireland have estimated genetic parameters for live weight and carcass composition traits using a multi-breed population rather than on an individual breed basis. The objective of the present study was to undertake genetic analyses of three lamb live weight and two carcass composition traits pertaining to purebred Texel, Suffolk and Charollais lambs born in the Republic of Ireland between 2010 and 2017, inclusive. Traits (with lamb age range in parenthesis) considered in the analyses were: pre-weaning weight (20 to 65 days), weaning weight (66 to 120 days), post-weaning weight (121 to 180 days), muscle depth (121 to 180 days) and fat depth (121 to 180 days). After data edits, 137 402 records from 50 372 lambs across 416 flocks were analysed. Variance components were derived using animal linear mixed models separately for each breed. Fixed effects included for all traits were contemporary group, age at first lambing of the dam, parity of the dam, a gender by age of the lamb interaction and a birth type by rearing type of the lamb interaction. Random effects investigated in the pre-weaning and weaning weight analyses included animal direct additive genetic, dam maternal genetic, litter common environment, dam permanent environment and residual variances. The model of analysis for post-weaning, muscle and fat depth included an animal direct additive genetic and litter common environment effect only. Significant direct additive genetic variation existed in all cases. Direct heritability for pre-weaning weight ranged from 0.14 to 0.30 across the three breeds. Weaning weight had a direct heritability ranging from 0.17 to 0.27 and post-weaning weight had a direct heritability ranging from 0.15 to 0.27. Muscle and fat depth heritability estimates ranged from 0.21 to 0.31 and 0.15 to 0.20, respectively. Positive direct correlations were evident for all traits. Results revealed ample genetic variation among animals for the studied traits and significant differences between breeds to suggest that genetic evaluations could be conducted on a per-breed basis.     

Breed, litter and parity effects on placental weight and placentome number, and consequences for the neonatal behaviour of the lamb

Lamb survival is impaired in low birth weight lambs, and those that are slow to stand and suck. Many of the factors that influence lamb vigour, such as parity, litter size, and breed, may exert their effects, at least partially, before birth by influencing placenta development. Our hypothesis was that retarded lamb behavioural development was due to differences in placentation in these animals. Data were collected from Blackface and Suffolk lambs in the first 2 h after birth and placentas were collected when delivered. Suffolk lambs, which were behaviourally slower and had lower rectal temperatures than Blackface lambs, were associated with larger but less efficient placentas (placental efficiency defined as foetal weight supported per g placenta) with fewer foetal cotyledons than Blackface placentas. Triplet lambs were significantly slower than twin or single lambs to suck and had lower rectal temperatures. Although placenta efficiency increased with litter size, placenta and cotyledon weight, and cotyledon number increased with twinning but not thereafter. It seemed likely that triplet lambs suffered some placental insufficiency in comparison to other litter sizes. Lambs born to first parity mothers were slower to stand and reach the udder than lambs of more experienced ewes, and first parity ewes also had smaller and less efficient placentas although cotyledon number was not affected. Male lambs tended to be slower than female lambs for most behaviours, although rectal temperatures were not affected. The sire of the lamb also influenced lamb behaviour and rectal temperature. Both lamb sex and lamb sire influenced the average weight of placental cotyledons, thus some of the sire effect on the behaviour and birth weight of his progeny might be mediated through placental development. Lamb neonatal vigour was correlated with placental efficiency suggesting that lamb behaviour immediately after birth is related to placental development and function.     

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.     

Genetic parameters for lameness,mastitis and dagginess in a multi-breed sheep population

The objective of the present study was to quantify the extent of genetic variation in three health-related traits namely dagginess, lameness and mastitis, in an Irish sheep population. Each of the health traits investigated pose substantial welfare implications as well as considerable economic costs to producers. Data were also available on four body-related traits, namely body condition score (BCS), live weight, muscle depth and fat depth. Animals were categorised as lambs (<365 days old) or ewes (⩾365 days old) and were analysed both separately and combined. After edits, 39 315 records from 264 flocks between the years 2009 and 2015 inclusive were analysed. Variance components were estimated using animal linear mixed models. Fixed effects included contemporary group, represented as a three-way interaction between flock, date of inspection and animal type (i.e. lamb, yearling ewe (i.e. females ⩾365 days but <730 days old that have not yet had a recorded lambing) or ewe), animal breed proportion, coefficients of heterosis and recombination, animal gender (lambs only), animal parity (ewes only; lambs were assigned a separate ‘parity’) and the difference in age of the animal from the median of the respective parity/age group. An additive genetic effect and residual effect were both fitted as random terms with maternal genetic and non-genetic components also considered for traits of the lambs. The direct heritability of dagginess was similar across age groups (0.14 to 0.15), whereas the direct heritability of lameness ranged from 0.06 (ewes) to 0.12 (lambs). The direct heritability of mastitis was 0.04. For dagginess, 13% of the phenotypic variation was explained by dam litter, whereas the maternal heritability of dagginess was 0.05. The genetic correlation between ewe and lamb dagginess was 0.38; the correlation between ewe and lamb lameness was close to zero but was associated with a large standard error. Direct genetic correlations were evident between dagginess and BCS in ewes and between lameness and BCS in lambs. The present study has demonstrated that ample genetic variation exists for all three health traits investigated indicating that genetic improvement is indeed possible.     

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.     

Economic weights of production and functional traits for Merinolandschaf, Romney, Romanov and Sumavska sheep in the Czech Republic

Economic weights of production and functional traits were estimated for the dual-purpose sheep breeds Romney (RY), Merinolandschaf (ML), Romanov (RV) and Sumavska (SA). A bio-economic computer model simulating the profit function for production systems with one lambing per year was used for the calculations. First, marginal economic values were calculated which were defined as partial derivatives of the profit function with respect to the average level for each trait. Applying gene-flow methodology, absolute and relative economic weights for direct and maternal components of the traits were then estimated for pure-bred production systems and systems which included partial terminal cross-breeding. The following traits were evaluated: birth weight, daily gain till weaning and during rearing, mature weight, dressing percentage, fleece weight, conception rate of ewe lambs and ewes, litter size at lambing (total number of lambs born per ewe lambing), survival rate of lambs at birth and till weaning and productive lifetime of ewes. Standardized economic weights were calculated as the product of the economic weight and the genetic standard deviation of each trait or trait component. The total economic importance was defined as the sum of the absolute (not taking into account the sign) standardized economic weights over all traits and trait components, and relative economic weights were then computed as the standardized economic weights expressed as percentages of total economic importance. The direct components of survival rate at birth and till weaning, the direct component of daily gain till weaning and litter size had the highest relative economic weights (greater than 10%) in pure-bred systems in all four breeds. In ML and RV, the maternal component of lamb survival rate till weaning also had a relative economic weight exceeding 10%. In systems with partial terminal cross-breeding for all four breeds, relative economic weights of maternal traits and trait components were slightly larger than in pure-bred production systems, particularly for litter size. Based upon comparison of relative economic weights of traits among breeds, separate breeding goals for RY and RV are recommended, whereas a common breeding goal is deemed appropriate for ML and SA.     

Never too late? Consequences of late birthdate for mass and survival of bighorn lambs

In strongly seasonal environments, the timing of birth can have important fitness consequences. We investigated which factors affect parturition date and how birthdate interacts with sex, maternal characteristics and environmental variables to affect the growth and survival of bighorn sheep (Ovis canadensis) lambs in a marked population in Alberta. Over 14 years, the estimated birthdate of 216 lambs ranged from 21 May to 18 July. Parturition date was heritable and genetically correlated with maternal mass the previous fall. Weaning a lamb delayed parturition the following year by about 7 days. Birthdate did not affect summer growth rate, but late-born lambs were lighter in mid September (the approximate time of weaning) than early-born ones. Birthdate did not affect survival to weaning, but late birth decreased survival to 1 year for male lambs. Forage quality, measured by fecal crude protein, did not affect survival to 1 year. Once we accounted for lamb mass in mid September, birthdate no longer affected the probability of survival, suggesting that late birth decreased survival by shortening a lamb's growing season. Because there was no compensatory summer growth, late-born lambs were smaller than early-born ones at the onset of winter. Our data highlight the importance of birthdate on life history traits and suggest that resource scarcity had more severe consequences for juvenile males than for females.     

A review of the effects of the Booroola gene (FecB) on sheep production

Booroola Merino (B^oM) ewes have a high ovulation rate and litter size which in 1980 was postulated to be due to the effects of a major gene (FecB). This was confirmed in breeding experiments and FecB was subsequently shown to be due to a mutation (BMPR-1B) on chromosome 6. The B^oM originated from an Australian commercial fine wool Merino flock (Booroola) and has been used in crossing experiments and for introgression of FecB into many breeds around the world to improve fecundity. The mutation has recently been found in native sheep breeds in India, China and Indonesia and it is likely that FecB in the Australian B^oM was derived from importations of Garole sheep from India in 1792 and 1793.The effects on production traits of the FecB mutation in a range of genetic comparisons, environments and production systems are reviewed. Comparisons involving B^oM crosses with various other breeds and contrasts of FecB homozygous (BB), heterozygous (B+) and non-carrier (++) genotypes in comparable background genotypes, including non-B^oM, have been summarised from 45 reports. The weighted mean effect for ewes carrying one copy of FecB (B+) was +1.3 (range +0.8 to +2.0) for ovulation rate and +0.7 (range +0.4 to +1.3) for litter size. The effect of a second copy (BB) was generally additive for ovulation rate, with little or no increase in litter size for BB ewes among B^oM crosses. However there was generally a further increase in litter size for BB ewes of about half the effect of one copy (B+) in the Indian and Chinese breeds. Poor lamb survival and lamb growth reduced the number of lambs weaned and total weight of lamb weaned by B+ ewes. Most studies still showed a small advantage for B+ ewes, although several reported negative effects. While embryo survival declines at higher ovulation rates, the effects of FecB per se are equivocal. There is some evidence of a higher non-pregnancy rate among homozygous BB ewes. Most studies reported lower birth weight and growth rate from B^oM cross lambs and lambs from crossbred ewes introgressed with FecB. However it is difficult to separate the effects of low background genetic merit for growth of the B^oM and the lower birth weight and growth rate of lambs from larger litters from the genetic effect of carrying FecB. There was little or no difference in growth rate between BB, B+ and ++ genotype lambs. For other traits including, seasonal oestrous activity, carcass and meat quality and wool production, there was no evidence of major effects of FecB. The opportunities for management and nutritional modification of FecB expression and implications for industry adoption are briefly discussed.     

Bio-economic modelling of sheep meat production systems with varying flock litter size using field data

Sheep meat producers derive the majority of income from sales of weaned lambs, determined by flock conception rates, litter size, and lamb survival. Field data from commercial flocks can inform sensitivity analyses of the effect of litter size on flock productivity, feed demand, and gross margin. This study adapted an established bio-economic model of a flock of breeding ewes informed by statistical relationships (from linear models) between flock litter size (lambs born per ewe lambing) and production factors (such as flock barren rate, litter birth type and lamb birth weight) identified using 156 145 animal records from the Irish national sheep breeding database. Sensitivity analyses were undertaken to investigate the effects of flock litter size on flock production, feed demand, and gross margin. Results showed that as flock litter size increased, the proportion of lambs born as multiples increased, with 14 % of lambs born as singles when flock litter size was 2.2 lambs born per ewe lambing. Flock gross margin increased from €2 205 to €7 730 as litter size increased from 1.0 to 2.0 lambs born per ewe lambing. As litter size increased from 1.0 to 2.2 lambs born per ewe lambing, flock gross margin increased linearly by, on average, €52 per 0.01 increase in litter size. At a litter size of > 2.2 lambs born per ewe lambing, flock gross margin increased on average €12 per 0.01 increase in litter size. At a litter size of 2.2 lambs born per ewe lambing, flock efficiency (at 65.0 kg of lamb weaned per ewe presented for breeding), weaning rate (at 1.5 lambs weaned per ewe presented for breeding; not including excess lambs from large litters sold within a week after birth and thus not weaned on-farm), and gross margin (at €8 500) began to plateau. The results indicate lower marginal returns in gross margin at very high flock litter size, due to the lower value of additional lambs born as triplets and quadruplets compared with single- and twin-born lambs. However, the diminishing economic returns occurred at higher flock litter size than are currently biologically achieved in most flocks. Quantification from this analysis demonstrates how the value of increasing the number of lambs born changes at very high flock litter size, which can inform the priorities and performance benchmarking for international sheep meat production industries.     

Genetic analysis of ewe productivity traits in Moghani sheep

Genetic and environmental (co)variance components for productivity traits in Moghani sheep were estimated using data from 1344 ewes. The data were collected in the Jafarabad breeding station, north-east of Iran, during a 13-year period (1995-2008). The studied traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB), litter mean weight per lamb weaned (LMWLW), total litter weight at birth (TLWB) and total litter weight at weaning (TLWW). A model including direct additive genetic effects as well as permanent environmental effects related to repeated records of ewe was the most appropriate model for all the studied traits. Genetic parameters were estimated applying restricted maximum likelihood (REML) procedure. Direct heritability estimate for LSB, LSW, LMWLB, LMWLW, TLWB and TLWW were 0.11, 0.02, 0.15, 0.07, 0.07 and 0.06, respectively. Corresponding values for repeatability estimates were 0.16, 0.19, 0.18, 0.11, 0.13 and 0.09. Genetic correlations between the studied traits ranged from −0.99 for LSB-LMWLB and LSW-LMWLB to 0.99 for LSB-TLWB. Phenotypic and environmental correlation estimates were generally lower than those of genetic ones. Estimates of permanent environmental correlation among traits were positive and medium to high. Although low direct heritabilities were estimated for the reproductive traits, as these traits are of interest then they should be included in a breeding program.     

Genetic determinism for within-litter birth weight variation and its relationship with litter weight and litter size in the Ripollesa ewe breed

Birth weight plays a central role in lamb survival and growth, and the knowledge of its genetic determinism has become essential in worldwide selection programmes. Within this context, within-litter birth weight variation (BWV) has been suggested as an attractive trait to homogenise litters in prolific species, although it has not been analysed in sheep. The objective of this study was to ascertain whether maternal additive genetic variance exists for BWV in Ripollesa ewes, and to study its genetic, permanent environmental and residual relationships with litter weight (LW) and litter size (LS) at birth. Data were recorded in the Ripollesa experimental flock of the Universitat Autònoma of Barcelona, between 1986 and 2005, and included 1 662 litters from 380 ewes, with 712 records of BWV and 1 530 records of LW. Traits were analysed with a multivariate animal model solved through Bayesian methodologies, and with a threshold characterisation of LS. Additionally, the effect of BWV on lamb survival was studied. Additive genetic variance was observed for BWV (h² = 0.061), as well as for LW (h² = 0.200) and LS (h² = 0.141). Nevertheless, genetic correlations among those traits were not substantial (BWV and LW = 0.151; BWV and LS = − 0.219; LW and LS = − 0.320) and suffered from a high degree of uncertainly, with the null correlation included within the highest posterior interval at 95%. Within-litter birth weight variation and LS showed a negative and large permanent environmental correlation ( − 0.872), and LW and LS were negatively correlated due to residual ( − 0.762) and permanent environmental ( − 0.449) random sources of variation. Within-litter birth weight variation influenced lamb mortality during the first 7 days of life (P < 0.05), increasing and decreasing survivability in heavier and lighter littermates, respectively. Nevertheless, stillbirths and lambs died after the 1st week of life were not affected by BWV (P>0.05). The low heritability found indicates that slow genetic progress may be expected from selecting for BWV. Close to zero genetic correlations suggest that this selection will probably not affect LS and LW, although some significant permanent and residual correlations must be taken into account. Further studies are needed to understand better the genetic architecture among these three reproductive traits.     

Relationships between lamb carcass quality traits measured by X-ray computed tomography and current UK hill sheep breeding goals

Genetic parameters were estimated between current UK hill sheep breeding goals and lamb carcass composition and muscularity traits derived using X-ray computed tomography (CT). To produce these estimates, a total of 648 lambs from two hill farms were CT scanned at weaning (ca 120 days of age), over 3 years, and total weights of carcass muscle (MUSC), fat (CFAT) and bone (BONE) and internal fat (IFAT) were predicted. Previously derived muscularity indices were also calculated for the hind leg (HLMI) and lumbar (LRMI) regions, to assess muscle shape. Data for current breeding goals (lamb performance and maternal traits) were also included from a total of 10 297 lamb records and 12 704 ewe records. Heritabilities were estimated for each trait and genetic and phenotypic correlations were calculated between each CT trait and other lamb or ewe traits. Moderate to high positive genetic correlations were found between CT-predicted tissue weights and breeding goals, which were also weights (lamb weaning weight, carcass weight, mature ewe weight, average weight of lambs reared by the ewe). CFAT was positively genetically correlated with ultrasound backfat depth at weaning (UFD) and subjective fatness grade at slaughter (MLCF), suggesting that carcass fat could be decreased using selection on any of these predictors. Ultrasound muscle depth at weaning (UMD) and subjective conformation score at slaughter (MLCC) had high genetic correlations with the muscularity indices (HLMI and LRMI), but correlations with MUSC were not significantly different from zero. This implies that selection to improve MLCC is likely to be increasing the 'roundness' of muscle shape in the high-priced carcass region, but having little impact on total lean meat yield. Correlations of CT traits with the other ewe traits (number of lambs weaned, number of lambs lost, longevity, fleece weight) were generally small or not significantly different from zero. The genetic parameters generated in this study can now be used in selection index calculations to assess the benefits of including lamb CT traits in future selection programmes for hill sheep.     

Inbreeding Effects upon Growth and Maternal Ability in Laboratory Mice

The effects of systematically increasing levels of inbreeding upon growth and postnatal maternal ability were determined in laboratory mice by utilizing the reciprocal crossfostering technique. Two experiments were conducted. The first included postnatal dams which were inbred 0, 12, 25 and 38% while corresponding levels in the litter were 0, 22, 38 and 50%, respectively. The second experiment included 0, 25, 50 and 73% inbred dams with litters inbred 0, 38, 59 and 79%, respectively. Increasing the level of inbreeding was found to linearly depress postnatal maternal performance. Young which had been suckled by the more inbred dams were smaller at 12 and 21 days of age than those which had been nursed by the more outbred dams. In the second experiment, these effects were carried over into the postweaning period. Increasing levels of inbreeding in the litter significantly depressed birth weight and weight at 12, 21, 42 and 56 days. The depressing effects of inbreeding in the litter were primarily linear for both males and females under the conditions of the more moderate levels of inbreeding included in the first experiment, but were curvilinear for females and linear for males in the second experiment. The curvilinearity in females was due to the general lack of depression until inbreeding had reached 50 to 60%, after which significant inbreeding depression developed.     

Effects of sex, litter size and periconceptional ewe nutrition on the ewe–lamb bond

Undernutrition restricted to the time around conception in sheep alters endocrine and metabolic responses in the offspring. Studies in rats suggest that such an early insult can also alter the behaviour of the offspring. We studied the effects of mild maternal periconceptional undernutrition (10–15% body weight reduction) on the lamb's response to separation from and reunion with the mother, and on the ewe–lamb bond, evaluated as the preference for each other over an alien ewe/lamb in a test enclosure, at 24 h, 1 and 4 weeks of age. Lamb birth weight was not affected by maternal nutrition. Maternal periconceptional undernutrition did not affect the lambs’ responses to separation and reunion (number of vocalisations, times to leave pen and achieve proximity with ewes) or the bond between ewes and lambs (percentage of time spent near their own dam/lamb). However, there were effects of sex, litter size and time on lambs’ responses to separation and reunion and on the ewe–lamb bond. Female lambs vocalised more during separation (P ≤ 0.01) and left the holding pen faster than males (P ≤ 0.05), and twins vocalised more than singletons (P ≤ 0.05). The time to leave the holding pen, achieve proximity with the ewes and number of vocalisations decreased with increasing postnatal age of the lamb (all P ≤ 0.001). Ewes showed a stronger preference for the lamb at 24 h and 1 week than at 4 weeks postpartum (P ≤ 0.001), whereas lambs followed an opposite trend, showing a lower preference for the mother at 24 h and 1 week and increased preference at 4 weeks of age (P ≤ 0.001). We conclude that periconceptional undernutrition does not affect offspring response to separation from the mother or the bond between ewes and lambs, but that these behaviours are affected by sex and litter size for up to 4 weeks after birth.     

Genetic parameter estimates for pre-weaning performance and reproduction traits in Markhoz goats

Genetic parameters for growth, mortality and reproductive performances of Markhoz goats were estimated from data collected during 1993–2010 at Markhoz goat Performance Testing Station in Sanandaj, Iran. For kid performance traits 3763 records were available for birth weight (BW), 2931 for weaning weight (WW), average daily gain (ADG) and Kleiber ratio (KR) (approximated as ADW/WW^0.75) and 3032 for pre-weaning mortality (PWM). For doe reproductive performance traits there were 2920 records available for litter size at birth (LSB), litter size at weaning (LSW), total litter weight at birth (TLWB) and litter mean weight per kid born (LMWKB), and 2182 for total litter weight at weaned (TLWW) and litter mean weight per kid weaned (LMWKW). Genetic parameters were estimated with univariate and bivariate models using restricted maximum likelihood (REML) procedures. Random effects were explored by fitting additive direct genetic effects, maternal additive genetic effects, maternal permanent environmental effects, the covariance between direct and maternal genetic effects, and common litter effects in different models for pre-weaning traits of kids. Also, in addition to an animal model, sire and threshold models, using a logit link function, were used for analyses of PWM. Models for LSB, LSW, TLWB, TLWW, LMWKB, and LMWKW included direct additive genetic effects, permanent environmental effects due to the animal as well as service sire effects. Estimated direct heritabilities were moderate for pre-weaning traits (0.22 for BW, 0.16 for WW, 0.21 for ADG, and 0.27 for KR and 0.29 for PWM), and low for reproduction traits (0.01 for LSB, 0.01 for LSW, 0.02 for TLWB, 0.03 for TLWW, 0.07 for LMWKB, and 0.06 for LMWKW). The estimates for the maternal additive genetic variance ratios were lower than direct heritability for BW (0.07) and KR (0.04). The estimate for the maternal permanent environmental variance ratios (c²) varied from 0.01 for KR to 0.07 for WW and ADG. The magnitude of common litter variance ratios (l²) was more substantial for BW (0.46) than the PWM (0.19) and KR (0.16). The estimate for the permanent environmental variance due to the animal (c²) ranged from 0.03 for LMWKB to 0.07 for TLWB and LMWKW, whereas service sire effects (s²) ranged from 0.02 to 0.04. The correlation between direct and maternal genetic effects were negative and high for BW (?0.51) and KR (?0.62). The genetic correlations between pre-weaning growth traits were positive and moderate to strong, as were genetic correlations between reproductive traits. Between BW and PWM the correlation was ?0.35. Phenotypic and environmental correlations for all traits were generally lower than genetic correlations.     

The effects of pasture availability for twin- and triplet-bearing ewes in mid and late pregnancy on ewe and lamb behaviour 12 to 24 h after birth

This experiment was conducted to evaluate the effect of offering ewes two different feeding levels, during mid and late pregnancy, on ewe and lamb behaviour 12 to 24 h after birth. Romney ewes, bearing twin (n = 80) or triplet foetuses (n = 56), were allocated to a pasture sward height of 2 or 4 cm between 70 and 107 days of pregnancy. In late pregnancy (day 107 to 147), half of the ewes were reallocated the alternate sward height, which produced four treatments: 2-2, 2-4, 4-2 and 4-4. Ewes were weighed on days 65, 92, 107 and 130 of pregnancy and lamb live weights were recorded 12 to 24 h after birth. Twelve to 24 h after birth the maternal behaviour score (MBS) of the ewes were determined, whilst their lambs were tagged. After the lambs were released, the behaviour of each ewe and her lambs was observed for 5 min. Ewe treatment and litter size had no effect on ewe MBS. However, as MBS increased (ewes stayed closer to lambs during tagging), ewes bleated less in a high-pitch and were quicker to make contact with their lamb. During the observation period, ewes in the 4-4 treatment had a greater percentage of their bleats in a low pitch (P < 0.05) than ewes in the 2-2 and 4-2 treatment (61.3% v. 41.3% and 38.8% low bleats, respectively) and more lambs born to 4-4 ewes (95%) bleated than lambs born to 2-2 ewes (84%; P < 0.05). However, lambs born to ewes in the 2-2 treatment bleated earlier than lambs in all other treatments (P < 0.05). Lambs born to 4-4 ewes were less likely (P < 0.05) to move towards their dam in order to make contact than lambs born to 2-2 or 4-2 ewes (3.1% v. 16.9% and 16.7%, respectively). These findings suggest that under the conditions of the present study, ewe nutrition had little effect on maternal behaviour. However, lambs born to ewes offered 2 cm pasture sward heights during mid and/or late pregnancy (2-2, 2-4 and 4-2 treatments) displayed behaviour that demonstrated greater 'need' whereas lambs born to ewes offered 4 cm during mid and late pregnancy sought less attention from their dam.     

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.     

Sex-differential effects of inbreeding on overwinter survival, birth date and mass of bighorn lambs

Although it is generally expected that inbreeding would lower fitness, few studies have directly quantified the effects of inbreeding in wild mammals. We investigated the effects of inbreeding using long-term data from bighorn sheep on Ram Mountain, Alberta, Canada, over 20 years. This population underwent a drastic decline from 1992 to 2002 and has since failed to recover. We used a pedigree to calculate inbreeding coefficients and examined their impact on lamb growth, birth date and survival. Inbreeding had a substantial effect on female survival: for a given mass in September, the probability of overwinter survival for inbred female lambs was about 40% lower than that of noninbred ones. Contrary to our expectations, inbred female lambs were born earlier than noninbred ones. Earlier birth led to inbred female lambs being heavier by mid-September than noninbred ones. There was a nonsignificant trend for inbred female yearlings to weigh more than noninbred ones. A stronger mass-dependent viability selection for inbred compared to noninbred female lambs may explain why surviving inbred females were heavier than noninbred ones. Survival of male lambs was not affected by inbreeding. Sex-differential effects of inbreeding may be a general pattern in sexually dimorphic mammals, because of sex-biased maternal care or sexual differences in early development strategies.     

母猪生产力性状的遗传分析

对二花脸猪、大白猪及其杂交一代３个群体共１６８６窝的生产力性状资料进行了遗传分析。用公畜模型估计了初生窝重、初生仔猪平均重、２０日龄窝重、２０日龄仔猪平均重、４５日龄窝重、４５日龄仔猪平均重的表型参数和遗传参数。与大白猪相比,二花脸猪抚育能力较强,生长速度较慢。前４个性状受母体影响较大,后２个性状受母体影响较小。６个性状的遗传力分别为０．２５１、０．２７７、０．３４１、０．３３０、０．２３５、０．