Effects of sire genotype on lamb performance at weaning in extensive sheep systems

A low finishing weight and poor carcass characteristics are major causes of lower incomes in extensive sheep flocks; however, the use of terminal sire crossbreeding would improve lamb performance and carcass traits under these conditions. The aim of this study was to evaluate sire breed effects on the performance of lambs born to Corriedale ewes in extensive sheep systems in Western Patagonia. A total of 10 Corriedale, 10 Dorset, nine Suffolk and seven Texel sires, 16 of which were under a genetic recorded scheme and 20 selected from flocks not participating in genetic improvement programmes, were used across six commercial farms for 2 successive years. Data were collected from 685 lambs of the four resulting genotypes. Overall, Corriedale lambs were 0.47 kg lighter at birth than crossbred lambs (P<0.001). Suffolk and Texel sired lambs required more assistance (P<0.01) at birth than Corriedale or Dorset sired lambs, with Suffolk sired lambs requiring the most assistance (8%). Ewes sired with Suffolk rams had larger (P<0.05) litters than ewes sired with Texel or Corriedale rams. Lamb live weight gain from birth to weaning was higher (P<0.001) in crossbred lambs compared with Corriedale lambs, therefore, crossbred lambs averaged 2.9 kg heavier BW (P<0.001) than Corriedale lambs. A significant sire breed x sire source interaction was detected for lamb live weight gain (P<0.05) and lamb live weight at weaning (P<0.01), showing that the heaviest lambs were from recorded sires, except for Suffolk crossbred lambs. Mortality rate to weaning was increased (P<0.05) in Suffolk cross lambs (31%), with Corriedale lambs showing the lowest (17%) mortality. Terminal sire breeds increased (P<0.001) cold carcass weight, with 13.8, 16.0, 15.2 and 14.9 kg for the Corriedale, Dorset, Suffolk and Texel sired lambs, respectively. Carcass length, kidney knob and channel fat, fat grade, grade rule and fat depth measurements were not affected by sire breed (P>0.05). Carcass conformation was higher in Texel sired lambs compared with Corriedale lambs (P<0.05), with Dorset and Suffolk sired lambs being intermediate. Crossbred lambs showed a greater (P<0.001) eye muscle than Corriedale. Commercial cuts were affected by sire breed, as a result of the Corriedale lambs being smaller and having lighter carcass than crossbred lambs. Significant improvement in lamb weights at weaning and carcass traits could be expected when using a terminal sire on Corriedale ewes in Western Patagonia. However, no advantages were detected with the use of recorded sires under these production systems.     

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.     

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.     

Lamb survival,glutathione redox state and immune function of neonates and lambs from periparturient Merino ewes supplemented with rumen-protected methionine

Wool growth in Merino sheep demands a high level of sulphur amino acids, competing with body growth and the immune system, which may play a role in increasing the risk of lamb mortality. The hypothesis that dietary supplementation of methionine (Met) to Merino ewes during the late stages of pregnancy will improve foetal growth and alter immune competency of ewes and lambs was tested in a total of 120 grazing, pregnant Merino ewes. Sixty ewes were group-supplemented with 6.3 g/d rumen-protected Met (Met-Plus) per sheep from day 111 of pregnancy until day 7 after lambing, and the other 60 animals were used as a non-supplemented Control. Lambs from Met-supplemented ewes tended to be 10% heavier than Control lambs (p = 0.10), which did not affected the survival rate at weaning significantly. The supplemented ewes had slightly higher concentrations of total glutathione (GSH) in plasma at lambing (p < 0.06), but there were no differences between 1 and 3 months post-lambing in GSH, glutathione disulphide (GSSG) and the GSSG:GSH ratio. The GSSG:GSH ratio in the blood of ewes was elevated at lambing (p < 0.05), hinting that ewes were undergoing increased oxidative stress. The Met supplementation elevated the total IgG concentration (p < 0.05) in lambs aged 4 and 6 weeks, but did not change the IgG concentrations in colostrum and in plasma of 1-week-old lambs, and white blood cell counts and leukocyte types. The trend towards higher lamb birth weights in the Met-supplemented group requires further investigation as this may influence survival at birth and weaning.     

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.     

Feed deprivation in Merino and Terminal sired lambs: (1) the metabolic response under resting conditions

The aim of this study was to examine the metabolic response to feed deprivation up to 48 h in low and high yielding lamb genotypes. It was hypothesised that Terminal sired lambs would have decreased plasma glucose and increased plasma non-esterified fatty acids (NEFA) and β-hydroxybutyrate (BHOB) concentrations in response to feed deprivation compared to Merino sired lambs. In addition, it was hypothesised that the metabolic changes due to feed deprivation would also be greater in progeny of sires with breeding values for greater growth, muscling and leanness. Eighty nine lambs (45 ewes, 44 wethers) from Merino dams with Merino or Terminal sires with a range in Australian Sheep Breeding Values (ASBVs) for post-weaning weight (PWT), post-weaning eye muscle depth and post-weaning fat depth (PFAT) were used in this experiment. Blood samples were collected via jugular cannulas every 6 h from time 0 to 48 h of feed deprivation for the determination of plasma glucose, NEFA, BHOB and lactate concentration. From 12 to 48 h of feed deprivation plasma glucose concentration decreased (P < 0.05) by 25% from 4.04 ± 0.032 mmol/l to 3.04 ± 0.032 mmol/l. From 6 h NEFA concentration increased (P < 0.05) from 0.15 ± 0.021 mmol/l by almost 10-fold to 1.34 ± 0.021 mmol/l at 48 h of feed deprivation. Feed deprivation also influenced BHOB concentrations and from 12 to 48 h it increased (P < 0.05) from 0.15 ± 0.010 mmol/l to 0.52 ± 0.010 mmol/l. Merino sired lambs had a 8% greater reduction in glucose and 29% and 10% higher NEFA and BHOB response, respectively, compared to Terminal sired lambs (P < 0.05). In Merino sired lambs, increasing PWT was also associated with an increase in glucose and decline in NEFA and BHOB concentration (P < 0.05). In Terminal sired lambs, increasing PFAT was associated with an increase in glucose and decline in NEFA concentration (P < 0.05). Contrary to the hypothesis, Merino sired lambs showed the greatest metabolic response to fasting especially in regards to fat metabolism.     

Fostering in sheep. IV. Use of restraint

Fostering an additional lamb on to a ewe with a single lamb of her own was attempted in Dorset, Corriedale and Merino ewes restrained by the neck in pens for up to 12 days. Fostering occurred more rapidly in Dorsets than in Merinos, and success rates tended to be higher in Dorsets (81%) than the other breeds (73% in Corriedales and 69% in Merinos). The use of screens at the level of the ewe's neck to limit her olfactory examination of the lambs was more successful than when full olfactory contact was allowed. The prevention of any close olfactory contact resulted in an intermediate rate of acceptance, even though acceptance was apparently based on olfaction, as shown by universal rejection of strange alien lambs. Acceptance tests done within a few minutes of release from restraint were found not to reflect accurately the final level of acceptance, since some lambs came to be accepted within a day of being released. Further acceptances, that developed several days after release into a flock of ewes and lambs, emphasize an important role of the lamb in maintaining contact with the ewe. With few exceptions, lambs accepted when released from the pens were still accepted after a week or so in the flock.Dorset ewes given one or two foster lambs in the absence of their own lamb accepted the fosters within 9 days.Restraint fostering had no apparent harmful effects on the ewes or lambs, but had the disadvantages of being laborious and of soiling the ewes' wool. It has the advantage of providing lambs with an assured milk supply, and could prove useful for ewes that have failed to accept lambs under other methods.     

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.     

Fertility in South Australian commercial Merino flocks: sources of reproductive wastage

To identify reasons for low fertility in the Merino in South Australia, we defined the extent and sources of reproductive wastage in flocks of maiden (n=14) and mature age (n=54) Merino ewes managed on 43 properties over 4 year. In a second study, reproductive wastage was examined in a very high ovulating flock of mature age South Australian Merino ewes heterozygous for the FecB gene, mated to lamb in either the autumn or spring. Losses in the latter flock were examined in less detail than the large-scale study, but allowed wastage to be partitioned between pre- and peri/post-natal sources. In the first experiment, reproductive wastage between mating and weaning was estimated at 59.7 potential lambs or ova lost per 100 ewes exposed to rams, representing 42.4% of ova shed. The main source of wastage occurred at lambing (55.6% of total loss), with death of twins a major contributor (35.3% of total loss). Other important sources of wastage were from partial failure of multiple ovulation (PFMO; 20.4% of total loss) and from ewes mating but not lambing (13.2% of total loss). Reproductive wastage did not vary with either age of ewe (maiden versus mature) or season of mating (October-December versus January-March). Mean ovulation rate, estimated as 141 per 100 ewes ovulating (range 100-200), varied with age of ewe (129 versus 144; maiden versus mature) but not with season of mating or year (1990-1991). Values for fertility, fecundity and lamb survival were 90, 127 and 73%, respectively. Fecundity of maiden ewes was lower than that of mature ewes (116 versus 130). Survival of single and twin lambs between birth and tail docking was 83 and 56%, respectively. Net reproductive efficiency, or lambs weaned per 100 ewes exposed to rams, averaged 81 (range 31-122). In the second experiment, mean ovulation rate of FecB Merino ewes was 316 per 100 ewes ovulating, with 242 ova (potential lambs) lost between ovulation and tail docking. This loss was equally shared between pre- and peri/post-natal sources (123 versus 119), and demonstrates severe limitation of the Merino to successfully bear and rear multiple litters. We concluded that future research in commercial Merino flocks be focused on lamb mortality, particularly of twins, and on PFMO, the major source of embryo loss.     

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.     

Feeding behaviour of artificially reared Romane lambs

A consequence of increasing litter size in sheep is that a portion of the lambs have to be reared artificially. Detailed information about the pattern of milk consumption of artificially reared lambs would help improve their management. The purpose of this study is to describe the individual and group feeding behaviour of 94 Romane artificially reared lambs from 5 to 28 days of age using an electronic automatic lamb feeder. Animals were located in four pens of 8 to 15 lambs of similar age with one teat per pen. They were fed ad libitum. In our experimental situation (group rearing, continuous lightning) on average a lamb made 1.4±0.7 visits to the teat per meal and 9.5±3 meals per day. Mean meal duration was 247±158 s and the mean daily time spent feeding was 38±25 min. The mean quantity of milk intake was 176±132 ml per meal and 1.68±0.8 l per day. With age, the number of daily meals and their duration decreased while the quantity of milk consumed per meal and per day increased. Females tended to make more visits to the teat per meal and perform more meals per day but their milk consumption per meal was lower. The feed conversion ratio was 1.36±0.2. Synchrony in feeding (group meal) was estimated as the percentage of lambs that wanted to access the teat within the same short period (relative group meal size). On average 65% of lambs in the pen wanted to access the teat within the same period, but for 35% of group meals the relative group meal size was >90%. There was no consistency in the order in which lambs accessed the teat during a group meal. Our evaluation suggested that electronic automatic lamb feeders are tools that can provide, on a large scale, data describing the feeding behaviour of artificially reared lambs. It is then possible to study factors influencing these traits in order to improve the outcome of artificially reared lambs.     

Heritability of ram mating success in multi-sire breeding situations

Multi-sire mating of a mob of ewes is commonly used in commercial sheep production systems. However, ram mating success (defined as the number of lambs sired by an individual) can vary between rams in the mating group. If this trait was repeatable and heritable, selection of rams capable of siring larger numbers of lambs could reduce the number of rams required for mating and ultimately lead to increased genetic gain. However, genetic correlations with other productive traits, such as growth and female fertility, could influence the potential for ram mating success to be used as a selection trait. In order to investigate this trait, parentage records (including accuracy of sire assignment) from 15 commercial ram breeding flocks of various breeds were utilised to examine the repeatability and heritability of ram mating success in multi-sire mating groups. In addition, genetic and phenotypic correlations with growth and female fertility traits were estimated using ASReml. The final model used for the ram mating success traits included age of the ram and mating group as fixed effects. Older rams (3+years old) had 15% to 20% greater mating success than younger rams (1 or 2 years of age). Increasing the stringency of the criteria for inclusion of both an individual lamb, based on accuracy of sire assignment, or a whole mating group, based on how many lambs had an assigned sire, increased repeatability and heritability estimates of the ram mating success traits examined. With the most stringent criteria employed, where assignment of sire accuracy was >0.95 and the total number of lambs in the progeny group that failed to have a sire assigned was<0.05, repeatability and heritability for log_e(number of lambs) was 0.40±0.09 and 0.26±0.12, respectively. For proportion of lambs sired, repeatability and heritability were both 0.30±0.09. The two ram mating traits (log_e(nlamb) and proportion) were highly correlated, both phenotypically and genetically (0.88±0.01 and 0.94±0.06, respectively). Both phenotypic and genetic correlations between ram mating success and growth and other female fertility traits were low and non-significant. In conclusion, there is scope to select rams capable of producing high numbers of progeny and thus increase selection pressure on rams to increase genetic gain.     

Nursing behavior in dam-reared Russian saiga (Saiga tatarica tatarica) at the San Diego wild animal park

This study was designed to examine the nursing patterns and related behavior of young saiga raised by their dams. Four captive born lambs were observed at weekly intervals during continuous 14 h watches for the first 7 weeks of life. One-week-old lambs were found to nurse at an average rate of 1.1 bouts per hour and nursed for an average of 14.6 seconds per bout. This high nursing frequency and the average total daily nursing time of 242 seconds decreased rapidly with age. Saiga lambs sampled solid food as early as 4 days of age and were nearly dependent on solid food by the age of 7 weeks. Communal nursing, in which one or more lambs would nurse from an unrelated adult female while she nursed her own, was common. Grooming of the lamb by the dam was never seen except immediately following birth. © 1994 Wiley-Liss, Inc.     

Distance recognition in ewes and lambs kept permanently indoors or at pasture

We tested the ability of Merino and Merino × Romanov ewes and lambs to recognise each other at a distance when given the choice between an alien partner and their own. Two groups of animals were studied. In the first group, multiparous ewes and their lambs were housed permanently indoors at a stocking-rate of 1 ewe/2 m². In the second group, ewes and lambs were run permanently outside in a paddock at a stocking rate of 1 ewe/500 m². Of animals living outside, 87% of ewes recognised their own lamb (100% of multiparous dams versus 84% of primiparous ones, P = 0.02). This differed significantly from a random choice. By contrast, the proportion of correct choices by ewes living inside (all multiparous) was significantly lower (64%) and did not differ from a random choice at the 5% level. Lambs reared outside recognised their dam in 95% of cases, versus 72% in lambs reared indoors (P = 0.01). Both frequencies differed significantly from a choice at random. It is concluded that the environmental conditions in which ewes and lambs are maintained can influence their ability to select their partners at a distance with the help of auditory and visual cues.     

Sperm production, testicular size, serum gonadotropins and testosterone levels in Merino and Corriedale breeds

The relationships between testis size, hormone secretion and sperm production were studied during the spring (December) and autumn (May) in rams of two breeds with different breeding seasons and body weights (Corriedale and Australian Merino) maintained on native pastures and under natural photoperiods in Uruguay. Blood samples were collected at 20-min intervals during a 260-360-min period in 13 rams (four Corriedale, nine Australian Merino) during the late spring and autumn. Rams were weighed and testis size was estimated by orchimetry at each time period. Sperm production was estimated during a 2-week period, 2 months before blood collection and during each week following every blood collection. There was no relationship between testicular size and sperm production measured at the same time, nor between live weight and sperm production. In contrast, testicular volume during the late spring was correlated with sperm production in the autumn (r = 0.65; P = 0.02). The autumn serum LH was higher in Corriedale than in Merino rams. LH pulsatility was unaffected by season, but LH pulse frequency tended to be higher in Corriedale than in Merino rams, particularly in the late spring (2.37 versus 1.56 pulses/6 h; P = 0.08). Serum testosterone concentration was similar in both breeds and seasons. FSH levels were higher in the late spring than in the autumn in both breeds (Corriedale: 2.83 +/- 0.48 versus 2.17 +/- 0.24 ng x mL(-1); Merino: 2.23 +/- 0.24 versus 1.88 +/- 0.17 ng x mL(-1)). FSH and testosterone concentrations during the late spring were positively correlated with autumn sperm production (P = 0.07 and P = 0.03, respectively). In conclusion, the present experiment suggests that LH secretion is not a good parameter for the prediction of sperm production. In contrast, in our conditions (breeds and native pastures) testicular size and testosterone or FSH concentrations from the late spring may be used to predict sperm production in the autumn.     

Feeding pregnant ewes a high-salt diet or saltbush suppresses their offspring's postnatal renin activity

If ewes consumed a high-salt diet or saltbush during the last 3 months of pregnancy and for 3 weeks after birth, we expected the renin activity of their lamb to be suppressed at birth and at 3 weeks of age. We also expected an increase in the concentration of cations other than sodium in the ewe's milk and an increase in the plasma Na concentration of the lamb at birth. To test these hypotheses, Merino ewes were fed a high-salt diet (14% NaCl) in an animal house and compared to control ewes eating a control diet (2% NaCl). In addition, we compared ewes grazing saltbush (about 13% salt in diet) to ewes grazing pasture from day 60 of pregnancy to 3 weeks after birth. Lambs born to ewes consuming saltbush had 85% lower (P < 0.001) renin activity than offspring from ewes consuming pasture at 3 weeks of age. Similarly, lambs born to ewes consuming a high-salt diet had 20% lower renin activity at birth and 3 weeks (P = 0.07). Feeding ewes a high-salt diet or saltbush altered the mineral composition of the milk; the largest change was a 10% increase in K levels (P 0.05). Consuming a high-salt diet or saltbush lowered the plasma Na of ewes at 130 days of gestation (by 3-5 mmol/l; P < 0.001), but only lambs from ewes fed the high-salt diet had a lower plasma Na at birth (P < 0.05). Suppression of the renin activity of lambs could lead to permanent physiological changes in salt balance in later life.     

Factors associated with lamb mortalities in Muzaffarnagari sheep

The Muzaffarnagari sheep, a mutton-producing breed of India, is generally known for its fast growth rate and high feed conversion efficiency. The study identified the causes of perinatal and postnatal deaths and factors contributing to the cause of mortalities in lambs. Data were recorded for 4628 lambs born to Muzaffarnagari ewes in single-sire matings from 165 rams, between 1978 and 2002. The least-squares means for overall lamb mortality from birth to 1 year of age in the flock was 12.6% (582/4628), while the overall pre- and post-weaning mortality rate averaged 6.6% and 6.0%, respectively. The mortality rate of the lambs declined as the lambs grew older. The major causes associated with lamb losses were pneumonia (31.4%), digestive disorders (14.6%), starvation (9.6%), endoparasitism (5.0%), septicaemia and toxaemia (10.1%), accidental (2.1%) and undetermined causes (27.2%), respectively. The main causes of early lamb mortality (within 15 days of birth) were pneumonia followed by starvation. The highest lamb mortalities occurred within the first 15 days of life. The year of birth of the lamb significantly affected (P < 0.01) the cumulative lamb mortality rate at all ages. The sire of the lamb also had a significant (P < 0.01) effect on lamb mortality rate at all ages. Lambs reared under an intensive feeding management system had a remarkably (P < 0.01) lower mortality rate than lambs maintained under a semi-intensive management system, at 3 months of age and later. The lamb losses were significantly (P < 0.01) higher in ram lambs than in females during the post-weaning stages. The linear regressions of lamb birth weight and dam weight at lambing were highly significant (P < 0.01) with lamb mortality rate during pre- and post-weaning stages. Logistic regression analyses revealed lambs maintained under a semi-intensive system, to be at a greater risk of dying from all ailments than lambs maintained under intensive feeding systems. Male lambs had greater risk of death from respiratory, digestive and other causes, compared to their female counterparts. The findings of this study revealed causes of pre-weaning lamb mortalities to be mainly due to a low birth weight and non-parasitic diseases (predominantly pneumonia). These factors must be considered in any lamb production system.     

Maternal influence on feeding site selection of male and female lambs

We conducted an experiment to determine whether early-life social learning of feeding site selection in lambs was sex-specific. Sixteen ewes and their new born lambs were used in a controlled experiment. Eight ewe–lamb pairs included a male lamb and the remaining eight a female lamb. All pairs were individually exposed to an experimental arena containing a safe and unsafe artificial feeding site (SFS, UFS) each consisting of nine bowls which contained either ground Bermuda grass hay (SFS) or ground alfalfa hay (UFS). The bowls in UFS were surrounded by bright orange traffic cones (visual cues). Half the ewes were trained with controlled electric shock to avoid UFS. Thus, pairs were randomly assigned to: (1) shock aversion training (SAT) to mothers of male lambs (MS); (2) SAT to mothers of female lambs (FS); (3) no aversion training (NAT, control) to mothers of male lambs (MC); and (4) NAT (control) to mothers of female lambs (FC). None of the lambs were subjected to SAT. During training, testing, extinction, and retraining ewe–lamb pairs were exposed to the arena together. Ewes were then removed from the experiment and two additional extinction phases were conducted with weaned lambs alone. Fear conditioning elicited UFS avoidance of both the trained ewes (means±s.e.m. % times observed in UFS during testing phase: FC=95.3±1.70; MC=94.4±4.87; FS=1.6±1.63; MS=0 ±0; P<0.01) and their naïve lambs (FC=83.8±6.07%; MC=76.6±6.56%; FS=30.4±7.90%; MS=33.9±9.23%; P<0.01). UFS avoidance in lambs occurred regardless of sex and tended to persist after weaning (% times observed in UFS during 1st post-weaning extinction phase: FC=92.6±4.50%; MC=89.8±6.09%; FS=45.1±10.57%; MS=43.5±10.42%; P=0.06). Fear conditioning in mothers appeared to alter sex-related differences in mother–infant behavioral synchrony by increasing and decreasing feeding synchrony of male and female lambs, respectively (FC: r=0.52, P<0.01; MC: r=−0.02, P=0.86; FS: r=0.14, P=0.26; MS: r=0.46, P<0.01). During the extinction phase mothers of ram lambs were observed feeding more often (FC=85.0±2.33%; MC=92.7±1.45%; FS=47.3±8.81%; MS=72±5.68%; P=0.02) and standing less often than ewes with daughters (FC=7.3±2.40%; MC=2.7±0.83%; FS=39.3±9.04%; MS=18.0±5.29%; P=0.06). This study suggests that social conditioning at an early age could be a viable tool to induce learning of feeding site avoidance in female and male lambs alike.     

Identification of fecundity gene (FecB) carriers using microsatellite markers and its effect on sheep weight

Abstract. Altogether 115 animals representing 5 genetic groups: 3 purebred Booroola Merino, Corriedale and Olkuska, and 2 Booroola crossbreds were included in the studies. In total 6 alleles from 97 bp to 119 bp in microsatellite OarAE101, and 5 alleles from 162 bp to 174 bp in BM1329 were identified. The marker of FecB gene presence seems to be an allele of 97 bp in the case of microsatellite OarAE 101 and 162 bp in the case of BM1329. Significant differences FecB carriers (Booroola-Corriedale) and non-carriers (Corriedale) in birth weight and at weaning at 100 days (males and females from twins) as well as weight gain during the first 28 days and 100 days were found. Purebred lambs showed higher values of the investigated traits.     

Caffeine supplementation of ewes during lambing may increase lamb survival

Perinatal mortality of lambs is on average 20% of lambs born in extensive Australian grazing systems, constituting a substantial production loss and welfare concern. Hypoxia resulting from prolonged or difficult births contributes to lower rates of lamb survival, and caffeine may reduce the effects of hypoxia. This study evaluated whether oral supplementation of grazing ewes with caffeine could improve lamb survival. Pregnant Merino ewes (n=492) which had been naturally mated to Merino rams in February/March were allocated to three replicates of control (no caffeine) or caffeine treatments. Caffeine was fed daily in troughs in each paddock at a rate of 1.6 g/ewe per day (estimated at 20 mg/kg live weight) from the day before the first lamb was born, for 14 days, with lambing continuing for 6 weeks. Intake was facilitated using 320 g/day per ewe of barley grain with molasses, which was fed to both treatments. The proportion of lambs born alive during the period of supplementation did not differ (P>0.05) between treatments. The proportion mortality of lambs to 1 day of age was lower (P=0.029) in the caffeine (0.01) compared with the control (0.16) treatment for lambs born during the 1^st week of supplementation, but not in later weeks. This difference in mortality for lambs born in the 1^st week of supplementation was maintained to marking age (caffeine 0.09; control 0.30; P=0.027). Extreme weather during the 2^nd week of supplementation may have prevented any reduction in mortality due to caffeine in that week. Feeding caffeine to a naturally lambing flock of grazing ewes may be a highly effective and commercially practical method of increasing lamb survival, but further research is needed to confirm these results, and caffeine be regulated for use.