Lambing Rate Research Articles

The effect of hCG treatment on Day 12 post-mating on ovarian function and reproductive performance of ewes and ewe lambs

The objectives of this study were to determine the effect of a single intramuscular injection of 200 IU hCG (Chorulon) on Day 12 post-mating on ovarian function and subsequent lambing performance in ewes and ewe lambs bred at synchronised oestrus during the breeding season and on the lambing performance of ewes induced to breed during late anoestrus. All animals were mated to rams at synchronised oestrus and on Day 12 post-mating given normal saline or 200 IU hCG. In Experiment 1, laparoscopic results showed that hCG treatment induced accessory corpora lutea in ewes (control = 0/7; hCG = 5/7) but not in ewe lambs (control = 0/7; hCG = 0/7). In Experiment 2, hCG treatment did not improve the lambing rate (control = 50; hCG = 57) or the litter size (control = 1.80; hCG = 1.96) in ewes (control = 100; hCG = 91). However, hCG treatment significantly ( P > 0.05) improved the lambing rate (control = 29; hCG = 58; P < 0.05) in ewes conceiving at the first oestrus after treatment. hCG treatment (control = 42; hCG = 42) also failed to improve the lambing rate in ewe lambs (control = 48; hCG = 41). In Experiment 3, hCG treatment had no significant ( P > 0.05) effect on the lambing rate (control = 72; hCG = 62) or the litter size (control = 1.59; hCG = 1.58) in ewes (control = 111; hCG = 115) induced to breed during anoestrus or on ewes returning to oestrus and conceiving after treatment (lambing rate: control = 86; hCG = 72; litter size: control = 1.44; hCG = 1.35). In conclusion, the data obtained in this study suggest that during the breeding season hCG may, by stimulating ovarian function, improve embryo survival in ewes conceiving at the first post-treatment oestrus. This effect, however was not observed in ewe lambs.

Effects of the absence of protozoa from birth or from weaning on the growth and methane production of lambs

Merino ewes (n 108) joined to a single sire were allocated into three flocks, with ewes in one flock being chemically defaunated in the second month of gestation. Single lambs born to defaunated ewes (BF lambs) were heavier at birth and at weaning than lambs born to faunated ewes (F lambs). After weaning, all BF and F lambs were individually housed then half of the F lambs were chemically defaunated (DF lambs). In trial 1, BF, DF and F lambs were offered a concentrate-based diet containing either 14 or 19 % protein for a 10-week period. Wool growth rate of BF lambs was 10 % higher than that of DF or F lambs and was increased 9 % by the high-protein diet. While there was no main effect of protozoa treatment on enteric methane production, there was an interaction between protozoa treatment and diet for methane production. BF and DF lambs produced more methane than F lambs when fed the low-protein diet but when fed the high-protein diet, emissions were less than (BF lambs) or not different from (DF lambs) emissions from F lambs. In trial 2, lambs were offered 800 g roughage per d and, again, methane production was not affected by the presence of protozoa in the rumen. The data indicate that while lambs without rumen protozoa have greater protein availability than do faunated ruminants, there is no main effect of rumen protozoa on enteric methane production by lambs fed either a concentrate or roughage diet.

Defatted Moringa oleifera seed meal as a feed additive for sheep

The objective was to evaluate use of defatted Moringa oleifera seed meal (DMM) as an additive in sheep diets. Effects of DMM on feed intake, diet digestibility, microbial N supply, blood metabolites and growth of lambs fed an oat-vetch hay based diet were evaluated using 24 Barbarine lambs in four groups. All lambs were fed hay ad libitum, and 100 g of soyabean meal (SBM) mixed with 0 (Control), 2 (Low), 4 (Medium) or 6 (High) g DM of DMM per day. A 45-day feeding study followed by a 6-day digestion study was completed. The DMM was higher ( P<0.001) in crude protein (592 g/kg DM versus 471 g/kg DM) and lower ( P<0.001) in NDFom (105 g/kg DM versus 169 g/kg DM) than SBM. Feeding DMM had no effect on hay intake, diet digestibility or N balance. Lambs grew at rates of 63.8, 88.5, 97.0 and 76.6 g/day, respectively (Q; P=0.076), possibly due the trend to an increase in the microbial N supply (Q; P=0.109) and the trend (Q; P=0.086) to higher N retention with higher levels of DMM in the diet. The highest daily gains tended (Q; P=0.076) to be highest in the lambs fed the intermediate levels of DMM. Results suggest that DMM has the potential to improve rumen fermentation, the medium levels are recommended as an additive to improve the growth rate of lambs fed hay-SBM diets.

Effect of supplementation of Sesbania sesban to lactating ewes on milk yield and growth rate of lambs

The present experiment was conducted to study the effects of supplementation of Sesbania sesban on the milk yield of ewes and growth rate of their lambs. The experiment was done with animals that had been fed for 16 months on a basal diet of teff straw supplemented with concentrates alone (0% S. sesban) or 95% of supplementary protein provided by S. sesban (accession 15019). Thirty lactating ewes and their single lambs of Ethiopian highland Menz sheep were used in this study. The post partum weight of ewes and birth weight of their lambs ranged between 16–22 kg and 1.3–2.4 kg. The ewes continued to be fed a teff straw basal diet and supplemented with two levels of S. sesban (0, and 95% of supplementary protein provided by S. sesban and the rest being provided by concentrates) for 3 months. Three weeks after birth lambs were offered a succulent green grass–legume mixture ad libitum. Dry matter and organic matter intake of basal feed and total feed, live weight at weaning and post partum daily body weight gain of ewes were not significantly different ( P > 0.05) between treatments. The milk yield of ewes was significantly affected ( P < 0.05) by dietary treatments. Ewes supplemented with S. sesban showed a 13% increase in milk production over ewes supplemented with concentrates. The peak lactation for ewes supplemented with S. sesban was higher and persisted longer than for ewes supplemented with concentrates. Lambs born from ewes supplemented with S. sesban had a significantly higher pre-weaning growth rate and were heavier at weaning ( P < 0.05) than lambs born from ewes supplemented with concentrates. We concluded that supplementation of S. sesban at 30% of the ration (0.98% of their body weight) during lactation improved milk yield of ewes and growth rate of lambs.

Nitric oxide buffers effects of angiotensin II on arterial baroreflex control of heart rate in conscious lambs

Previously, we showed that both nitric oxide (NO) and angiotensin II (ANG II) modulate the arterial baroreflex control of heart rate soon after birth. To test the hypothesis that NO buffers the effects of ANG II through activation of AT1 receptors early in life, three experiments were carried out at intervals of 48 h and in random order in two age groups of conscious, chronically instrumented lambs: ∼one week (N=9) and ∼six weeks (N=11): The arterial baroreflex was assessed before and after administration of the selective AT1 receptor antagonist, ZD 7155, and vehicle (experiment one), ZD 7155 and L‐NAME (experiment two), or vehicle alone (experiment three). There were no effects on any of the parameters governing the arterial baroreflex at six weeks after ZD 7155 with or without L‐NAME or vehicle. In contrast, after ZD 7155 at one week there was a decrease in the heart rate range, an increase in minimum heart rate, and an increase in maximum gain. After L‐NAME, in the presence of ZD 7155, these changes were exacerbated at one‐ but not six weeks. These findings support the postulate that there is an age‐dependent interaction between ANG II and NO in modulating the arterial baroreflex control of heart rate.

Partial replacement of concentrate with tomato pulp and olive cake-based feed blocks as supplements for lambs fed wheat straw

The replacement value of feed blocks tomato pulp (TP-FB) or olive cake (OC-FB) for a concentrate (wheat bran and processed barley, 1:2) was evaluated using 25 Barbarine lambs, fed wheat straw (WS) based diet, in a 75-day feeding trial followed by a total collection period (4 days adaptation and 6 days collection). Wheat straw was fed ad libitum and supplemented with (1) 500 g concentrate (control, C); (2) 250 g C and TP-FB (TP-FB + 0.5C); (3) 250 g C and OC-FB (OC-FB + 0.5C); (4) 125 g C and TP-FB (TP-FB + 0.25C); or (5) 125 g C and OC-FB (OC-FB + 0.25C), in a randomised block design. Except control-animals, lambs had free access to feed blocks. Metabolisable energy (ME, MJ/kg dry matter [DM]) and crude protein (g/kg DM) contents of the concentrate, TP-FB and OC-FB were 13.8 and 122, 11.2 and 154, and 11.0 and 147, respectively. Type of feed block had no effect on WS intake but increased total intake. Estimated ME intakes were 7.2, 8.5, 8.3, 8.3, and 7.3 MJ/day, respectively. Diets including FB exhibited higher digestible CP intakes than the control diet (P<0.01). Nitrogen balance ranged between 2.7 and 3.9 g/day. N retention and the efficiency of microbial nitrogen supply tended to increase with FB provision (P>0.05 and P=0.057, respectively). Compared to the control diet, FB supply had no effect on the growth rate of lambs (P>0.05). The response of lambs was in general better with diets containing OC-FB than those supplemented with TP-FB. The absence of urea and rapeseed meal in TP-FB could be among the reasons why sheep responded better to OC-FB. Feed conversion rates were higher with TP-FB diets than with OC-FB diets. Although results obtained with TP-FB were similar to those observed on lambs receiving OC-FB, the economic evaluation calls for revision of the formula of tomato-pulp-based feed blocks. Energy enrichment of OC-FB and TP-FB seems necessary for efficient utilisation of high levels of N in these feed blocks. It is concluded that OC-FB are cost-effective alternative supplements and allow farmers to reduce by 0.75 the amount of local concentrate used, while TP-FB allow a 0.5 reduction.

Effects of parity and litter size on maternal behaviour in Kivircik ewes

Aim was to investigate effects of parity and litter size on grooming lambs, responses to sucking attempts of lambs, maternal behaviour score, and survival of their lambs in Kivircik ewes. Proportion of time spent grooming lambs was 0.34, 0.42, 0.41 and 0.45 in first, second, third and fourth parity ewes (P>0.05). Multiparous ewes stood and allowed lambs to suck for a greater proportion of sucking attempts compared with primiparous ewes. When the lamb attempted to suck, circling was the behaviour most often observed among ewe movement behaviours, whereas backing and moving forward behaviours were observed very rarely. Mean maternal behaviour score given to single and twin-lambed ewes were 2.87 and 3.36, respectively (P<0.05). The effect of ewe parity on survival of their lambs was not significant. However, mortality rate of twin lambs (19.2%) was significantly higher than that of single lambs (5.7%). Kivircik ewes did not increase the total maternal care to their lambs when they lambed twins, and time that the lamb received grooming attention in twin born lambs was about half of the time received grooming in single born lambs. Furthermore, survival rate of the twin born lambs was lower than that of single born ones.

Field evaluation of an orf vaccine in sheep and goat flocks with high neonatal mortality

A high percent of annual neonatal mortality attributed to orf infection was observed between 2001 and 2004 in 2 sheep and 2 mixed (sheep and goat) flocks of Northern Greece. In order to protect the neonatal lambs and kids from orf infection a commercially available live orf vaccine was used. Pregnant sheep and goats were vaccinated subcutaneously a month before parturition, while 10 sheep and 10 goats in each flock remained unvaccinated and were used as negative controls. The vaccine was significantly effective (P&lt;0.05) in reducing the orf lesions and the mortality rate in lambs and kids of the 4 flocks. During the next year 3 of the 4 flocks were revaccinated. A significantly low percentage of orf lesions and neonatal mortality continued to occur in revaccinated flocks, while a significant percentage (P&lt;0.05) of orf lesions and neonatal mortality reappeared in the nonrevaccinated flock. The antibody titres in vaccinated sheep and goats were increased significantly on days 60 and 105 post-vaccination, while the titres in the controls remained low (P&lt;0.05).

Sire and growth path effects on sheep meat production. 1. Growth and carcass characteristics

The growth and carcass characteristics of 627 crossbred lamb progeny from 20 Poll Dorset sires was studied. The sires were selected on the basis of Australian sheep breeding values (ASBVs) for postweaning growth (PWWT), depth of loin muscle (PEMD) and depth of subcutaneous fat (PFAT). Lambs were weaned either at 20- or 30-kg liveweight and then within each of these groups were maintained at their weaning weight for 55 days or fully fed, giving four treatment groups. Restricted lambs were realimented subsequent to the period of feed restriction and all lambs within each treatment group were slaughtered when their mean liveweight reached 45 kg. After adjusting for the weaning group and weaning age, liveweight at weaning depended on birthweight, rearing type and sex. For the late-weaning group, it also depended on whether the lamb was born as a single or a multiple and on sire ASBVs for PWWT and PEMD. This was such that liveweight increased by 0.14 ± 0.05 kg for each unit increase in sire ASBV for PWWT and decreased by 0.55 ± 0.20 kg for a unit increase in sire ASBV for PEMD. During the period of feed restriction, sire ASBV for PWWT had an effect on the growth rate of lambs in all treatments with a coefficient of 1.67 ± 0.52. Lamb growth rate during the realimentation phase increased with increasing ASBVs for PWWT at a rate estimated as 2.21 ± 0.49 g/day for each unit increase in PWWT. Early-weaned (20 kg), restricted lambs grew on average 26.0 ± 3.4 g/day faster during the refeeding period than the early-weaned, fully fed lambs, and for late-weaned lambs (30 kg) the difference was 35.5 ± 5.4 g/day. Lambs subjected to a restricted intake of pasture produced carcasses 0.79 ± 0.32 mm fatter on average than those fully fed as measured at the GR site (110 mm from the midline over the 12th rib). As the sire PFAT ASBV increased, the carcasses of the progeny were fatter at the GR site, fat C site (over the longissimus muscle at the 12th rib), the rump site (30-mm distal to the lumbar–sacral junction over the gluteus medius muscle) and in terms of carcass fat percentage. As the sire PEMD ASBV increased, progeny carcasses had larger loin muscle cross sectional areas, and as the sire PFAT ASBV increased, there was a decrease in loin cross sectional area. There was no impact of treatment group on lean percentage. As the sire PFAT ASBV increased, the carcasses contained less lean and as PEMD ASBV increased, the carcasses contained more lean equating to a potential 2% increase given the range of ASBVs in the experiment, which represents ~0.4 kg lean on average.

Effect of group size on feed intake, aggressive behaviour and growth rate in goat kids and lambs

The effects of different group sizes on feed intake, growth and behaviour in penned kids and lambs were studied in an experiment (Exp. 1) with 30 kids and 30 lambs used in 3 periods. In each period, animals were divided into five group sizes. The group sizes were one, two, three, four or five animals per pen. In a second experiment (Exp. 2) 36 kids and 36 lambs were allotted to two groups of one and five animals per group. The diet consisted of Jackfruit ( Artocarpus heterophyllus) and Acacia ( Acacia mangium) foliages, sugar-cane ( Saccharum officinarum) and concentrate. The foliages were given ad libitum, equal to 130% of intake of fresh matter of the group the previous day, and concentrate and sugar-cane were given at a level of 10 g dry matter (DM)/kg initial body weight. The time for each period in Exp. 1 was 21 days, with the last 7 days for data collection. The behaviour observations were done during the last 4 days of each data collection period. The time for Exp. 2 was 84 days. In Exp. 1, the kids had a higher total DM intake (DMI) ( P = 0.011) and DMI of Jackfruit ( P < 0.001) than the lambs. Total intake increased linearly as group size increased ( P = 0.03). When feeding Jackfruit or sugar-cane aggressive behaviours recorded per pen or per animal increased linearly with group size. In Exp. 2, there was no difference in total DMI between kids and lambs, but kids had a significantly higher DMI of Jackfruit and a lower DMI of sugar-cane. Total DMI and DMI of Jackfruit and sugar-cane were similar for the group sizes of five animals and one animal, but kids showed a higher total intake and intake of Jackfruit in the group sizes of five animals, while a higher intake was obtained in single pens for lambs. The weight gain was higher ( P < 0.05) for the lambs compared to the kids, but similar for the animals in the group size of one or five animals. The feed conversion ratio (FCR) was significantly lower for the lambs compared to the kids, but not different between group sizes. The water intake of the lambs was higher ( P < 0.05) than that of the kids in both experiments and the animals in the pens with high density drank more water than the animals in individual pens only in Exp. 2. In conclusion, increasing the number of animals in the pens increased feed and water intake and also aggressive behaviours and did not improve growth rate or feed conversion ratio.

Plasma leptin in growing lambs as a potential predictor for carcass composition and daily gain

Leptin is an adipocyte derived hormone and correlates highly to the extent of body fat tissue. The aim of this study was to determine if leptin could serve as an early predictor for carcass composition and final growth rate in lambs with special emphasis on size and cellularity of the different body fat depots. Thirty intact male ad libitum fed lambs were blood sampled at 20, 25, 30, 35, and 40 kg live weight. After slaughtering at 40 kg, lean and the visceral, subcutaneous and intermuscular fat were measured by dissection. The fat cell diameter was determined in subcutaneous and perirenal fat. Average daily gain from birth to slaughter correlated to leptin only at 30 and 35 kg live weight ( r = −0.56 and −0.61, P < 0.01) and thus leptin cannot be regarded as a suitable early predictor for growth rate. That goes for the prediction of subcutaneous and intermuscular fat, too; because no relationships were detected between early leptin concentrations and the amount of these tissues. Leptin concentrations measured just before slaughter were related to all fat tissues except the pelvic and intramuscular fat. Among the visceral fat depots, omental fat expressed the highest correlations to leptin ( r = 0.60, P < 0.001). Additionally, leptin concentrations at 35 and 40 kg live weight increased with increasing fat cell diameters ( r = 0.38, P < 0.05 to r = 0.59, P < 0.001). This study indicates that leptin concentration measured in the slaughter weight range has the greatest potential to assess body fat content, whereas an earlier prediction does not seem to be feasible. Further studies should clarify if these results are reproducible for other breeds or species.

Prenatal exposure to excess testosterone modifies the developmental trajectory of the insulin-like growth factor system in female sheep.

Experimental elevation of maternal testosterone (T) from 30 to 90 days of gestation leads to intrauterine growth retardation (IUGR) and increased prepubertal growth rate in female lambs. This study tested the hypothesis that prenatal T treatment during mid-gestation alters the trajectory of the fetal insulin-like growth factor (IGF)-insulin-like growth factor binding protein (IGFBP) system to promote IUGR and subsequent postnatal catch-up growth in female lambs. Plasma IGF-I and IGFBPs were measured by radioimmunoassay and Western ligand blot, respectively, on 65, 90 and 140 days (d) of gestation, at birth, approximately 5 months (prepubertal, the catch-up growth period), and approximately 9.5 months (postpubertal). Northern blot analysis was used to measure hepatic mRNA content of IGF system components during fetal stages. At fetal 65 d, plasma protein and hepatic mRNA content of IGFBP-1, an inhibitor of IGF bioactivity, was elevated in prenatal T-treated fetuses although body weight did not differ. There was a transient increase in plasma IGF-I and IGFBP-3 concentrations at fetal 90 d in prenatal T-treated fetuses. Hepatic IGF-I mRNA and plasma IGFBP-3 content were reduced by 140 d when body weight was reduced in prenatal T-treated fetuses. Plasma IGFBP-2 content was significantly reduced in prenatal T-treated newborns, but by 4 months these females had significantly higher circulating IGF-I and IGFBP-3 concentrations and faster growth rates than control females. After puberty, plasma IGF-I remained elevated in prenatal T-treated females. These findings provide evidence that prenatal T excess programmes the developmental trajectory of the IGF/IGFBP system in female sheep to reduce IGF bioavailability during IUGR and increase IGF bioavailability during prepubertal catch-up growth.

Evaluation of the ovine callipyge locus: IV. Genotypic effects on reproductive traits1,2

A resource population of ewes derived from Dorset and Romanov grandparents was generated over 5 yr to provide genotypic and phenotypic data to estimate effects of each callipyge genotype on component traits of reproduction. Effects on ovulation rate were estimated from data recorded by examination of ovaries from serially slaughtered ewe lambs (n = 174) born in 1994 and 1995. Productivity and longevity through 5 yr of age were recorded on a total of 265 F2 ewes produced in 1996 through 1998. Number of lambs born, birth weights, and weaning weights of lambs were calculated for each ewe. Weaning weight was recorded for each lamb and adjusted for age to 56 and 32 d for dam- and nursery-reared lambs, respectively. Longevity was determined as a binary trait based on the presence or absence of the ewe in the breeding flock at 5 yr of age. Ewes generated 937 records for breeding weight and 925 records for conception rate, which was determined on ewes exposed and still present at the start of each lambing season. Seven hundred seventeen records were analyzed for traits based on the number of ewes lambing. Genotypes for the causative callipyge mutation were determined using a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry assay. Each ewe was classified into 1 of 4 genotypes; NMatNPat, NMatCPat, CMatNPat, or CMatCPat, where N represents wild type and C represents the mutant allele. The mean ovulation rate of the ewe lambs genotyped NMatNPat was greater (P < 0.02) than that exhibited by NMatCPat; however, the estimated difference of 0.25 ovum in the ewe lambs did not affect the number born. The live weight of NMatCPat ewes at breeding was 2.5 kg less than that of other genotypes (P < 0.01). The callipyge genotype class did not significantly affect conception rates, fecundity, maternal ability, or ewe longevity. Maintaining a ewe flock to produce homozygous mutant rams for use in terminal sire mating systems presents no unusual problems from a reproduction standpoint.

10 EFFECTS OF INSEMINATION TIME, BREED, AND INSEMINATOR ON FERTILITY OF EWES INTRAUTERINALLY INSEMINATED WITH FROZEN - THAWED SEMEN IMPORTED FROM NEW ZEALAND

Artificial insemination, especially with the use of frozen semen, is one of the important tools for embryo transfer program in sheep. The present study investigated the effects of insemination times, breeds, and two inseminators on the fertility of ewes intrauterinally inseminated with frozen–thawed ram semen imported from New Zealand. At 8 sheep farms located in Hokkaido, Japan, during the breeding season (October to December) in 2005, a total of 64 mature (1- to 6-year old) Suffolk (32 heads) and Polled Dorset (32 heads) ewes were used. The ewes were treated with controlled intravaginal drug release (CIDR containing 0.3 g progesterone; Pharmacia &amp;amp; Upjohn, Ltd., Auckland, New Zealand) for 12 days and an injection of 500 IU equine chorionic gonadotropin one day before CIDR removal. The fixed-time intrauterine inseminations (early: 43–46 h; late: 47–50 h) after CIDR removal were performed using the frozen–thawed semen from a Suffolk and Polled Dorset ram by two inseminators. The effects of breeds (Suffolk and Polled Dorset), fixed-time insemination times (early and late phases), and two inseminators on pregnancy (number of pregnant ewes/number of ewes inseminated, 60 days after insemination) and lambing (number of lambed ewes/number of ewes inseminated) rates were analyzed by chi-square test. The prolificacy was compared by Student&amp;apos;s t-test, and differences were also analyzed by Tukey&amp;apos;s omega procedure. The effect of the different farms on fertility was not examined due to the small numbers of ewes per farm. Pregnancy (60.0 and 72.4%, respectively) and lambing (60.0 and 71.4%, respectively) rates were not significantly different between Suffolk and Polled Dorset ewes. The inseminators also did not affect pregnancy (62.6 and 68.8%) and lambing (62.6 and 67.7%) rates. For the insemination times, the lambing rate tended to be higher (P ≤ 0.10) in the early insemination than in the late insemination (76.7% and 53.6%, respectively). The present results show acceptable fertility in ewes inseminated with Suffolk and Polled Dorset frozen semen imported from New Zealand. The early intrauterine insemination (43–46 h after CIDR removal) tended to result in higher fertility than the late insemination (47–50 h after CIDR removal). From 38 lambed ewes, 60 newborn lambs were produced, and this has provided new blood lines of Suffolk and Polled Dorset sheep in Japan.

Carrying the FecB (Booroola) mutation is associated with lower birth weight and slower post-weaning growth rate for lambs, as well as a lighter mature bodyweight for ewes

The present study was conducted in an Assaf flock in which the FecB (Booroola) mutation was segregated to determine whether the FecB mutation affects birthweight and the pre- and post-weaning growth rate of ewe lambs, as well as the mature bodyweight of ewes. Significant differences (P = 0.01) in birthweight (mean +/- s.e.m.) were found between BB ewe lambs (4.03 +/- 0.08 kg) and B+ and ++ ewe lambs (4.16 +/- 0.04 and 4.32 +/- 0.07 kg, respectively), which themselves did not differ significantly (P > 0.05). An FecB-associated maternal effect on the birthweight of ewe lambs was also detected, with the birthweight of lambs born to BB mothers (3.93 +/- 0.08 kg) being significantly (P < 0.0001) different from the birthweight of lambs born to B+ and ++ mothers (4.26 +/- 0.04 and 4.33 +/- 0.07 kg, respectively), which did not differ significantly. The genotypes of the lambs did not affect their preweaning growth rate. However, the post-weaning growth rate of ewe BB lambs (274 +/- 5 g day(-1)) was significantly (P = 0.05) different from the similar (P > 0.05) post-weaning growth rates of B+ and ++ lambs (284 +/- 3 and 290 +/- 4 g day(-1), respectively). The genotype at the FecB locus also affected the mature bodyweight of ewes, with that of BB ewes (67.3 +/- 1.4 kg) being significantly (P < 0.001) different from the similar mature bodyweight of B+ and ++ ewes (70.8 +/- 1.1 and 70.1 +/- 1.7 kg, respectively).

Genetic and nutritional regulation of lamb growth and muscle characteristics

Combined actions of nutrition and genetic regulation of the growth rate of lambs as well as the physical, biochemical, and eating quality characteristics of their skeletal muscle were assessed in a major field experiment. Data arising were collated and integrated to consolidate findings made at the farm, animal, tissue, cellular, and gene expression levels. At the farm level, increased nutrient availability significantly increased the growth rate of crossbred lambs and increased the growth advantage resulting from the use of sires with high estimated breeding values (EBV) for growth. In contrast, the extra depth of the M. longissimus thoracis et lumborum (EMD) arising from sires with a higher EBV for this trait was constant irrespective of nutrition. Ewe liveweight and body condition were critical in determining the pre-weaning nutrition and growth of lambs, with the LOW plane of nutrition causing stunting of forelimb bones and changes to the allometric growth coefficients for carcass lean and fat. The EBV of the sire for muscling (PEMD) influenced several non-muscling traits, and interactions with nutrition suggested that on HIGH nutrition, absorbed nutrients were partitioned away from wool and fat accretion and towards protein accretion in lambs having superior muscling genetics. Expression levels of known myogenic factors in muscle, together with a suite of peptides and proteins whose identity and levels were determined by proteomic screening, contributed to improved understanding of the mechanisms underpinning nutritional and genetic regulation of skeletal muscle development. The study revealed the need for caution in the use of indirect markers of growth or composition, with their usefulness being constrained if the localisation of the response to selection is specific to parts of the carcass where the selection had initially been concentrated. As well, the possibility that much of the variation explained by potential physiological markers can be accounted for by non-invasive measures of growth and fatness currently used by Australian farmers must be considered.

Productive and reproductive performance of Romney Marsh and Merino Branco sheep in the Azores under different feeding regimens

The objective of this study was to compare the productive and reproductive performances of Romney Marsh (RM) and Merino Branco (MB) ewes in the Azores. In a preliminary trial, fertility, prolificacy and fecundity of 25 RM and 27 MB ewes, mortality rate of lambs born and growth rate of lambs (14 RM and 20 MB) from birth to weaning at 24 kg live weight were determined. In a second trial following weaning, the same group of lambs were raised on pasture and supplemented either with concentrate or maize silage until slaughter (101 days later), and growth rate, carcass and meat characteristics were evaluated. Reproductive indices (fertility: 96% versus 93%; prolificacy: 117% versus 140%; fecundity: 112% versus 130%) and mortality rates (18% versus 17%) for RM and MB, respectively, were not significantly different. Pre-weaning gain was higher ( P < 0.05) in RM lambs than BM lambs (236 ± 8.6 g/day versus 214 ± 5.8 g/day). After weaning, RM lambs grew 20% faster than MB when supplemented with concentrate, but 16% slower when supplemented with maize silage ( P < 0.05). Growth of males was higher than that of females (110.3 ± 10.8 g/day versus 73.3 ± 9.3 g/day, P < 0.001). Lambs supplemented with concentrate grew twice as much as animals supplemented with maize silage (129.9 ± 9.8 g/day versus 60.5 ± 3.8 g/day, P < 0.01). Dressing percentage was not affected by breed, diet or sex. Characteristics of carcass and meat did not differ between breeds. Supplementation with concentrate resulted in thicker, fatter and wider carcasses ( P < 0.01) compared to supplementation with maize silage. It was concluded that the RM and MB sheep breeds are not very different in terms of growth potential and carcass characteristics. RM performed better with improved feeding conditions, while MB was less affected when food quality declined. MB appears to be a good alternative breed for exploitation in the Azores.

The effect of progesterone supplementation post mating and shearing of ewes in early pregnancy on the reproductive performance of ewes and birthweight of lambs

AIM: To determine whether short-term progesterone supplementation post mating or shearing of ewes in early pregnancy affected either the proportion of ewes that lambed or that had multiple lambs, or the birthweight of lambs. METHODS: Romney ewes (n=457) were synchronised in oestrus using controlled internal drug-releasing (CIDR) devices containing progesterone, and mated to Romney rams over a 5-day period. The mid-point of mating (Day 0) occurred 2 days after the withdrawal of CIDR devices. Ewes mated (n=397) were randomly allocated to one of four treatment groups: shearing at Day 5, shearing at Day 30, no shearing, and no shearing plus progesterone supplementation using a CIDR device inserted on Day 3 for 6 days. During the period from Day 5 to Day 27, six harnessed Suffolk rams were placed with the ewes and matings recorded. At Day 48, all ewes that did not return to the Suffolk rams were scanned for pregnancy using ultrasound. At Day 140, single- and multiple-bearing ewes were set-stocked at 15.1 and 12.2 ewes/ha, respectively, and equivalent numbers of ewes from each treatment group were placed in each paddock. Blood samples from 10 unshorn and 10 progesterone-supplemented ewes were collected on Days 3, 6 and 9, and analysed for plasma progesterone concentrations. Lambs were identified to their dam and weighed within 12 h of birth, and again at 27 and 93 days after the mid-point of lambing. The ewes were weighed at regular intervals throughout the trial. RESULTS: Plasma progesterone concentrations of supplemented ewes were higher than those of unsupplemented ewes (3.28 vs 1.75 ng/ml) on Day 6 (p=0.02) but not on Day 9 (4.58 vs 4.63 ng/ml). Treatment of ewes had no effect on either the proportion of ewes which lambed to the synchronised mating period or that had multiple lambs. Lambs born to ewes shorn at Day 30 tended (p=0.09) to be heavier at birth (by 0.28 kg) than those born to unshorn ewes but this effect was not evident when data were corrected for length of gestation. Neither shearing at Day 5 nor progesterone supplementation had any effect on the birthweight of lambs, and the treatment of ewes had no effect on the survival rate of lambs to weaning. CONCLUSIONS: Progesterone supplementation for 6 days beginning 3 days post mating did not increase either the proportion of ewes that lambed or that had multiple lambs, or the birthweight of lambs. Shearing 5 days after mating had no significant effect on the reproductive performance of ewes and need not be avoided, but is unlikely to result in an increase in lamb birthweight. Shearing ewes at Day 30 may result in an increase in the birthweight of lambs but, ideally, ewes should be further advanced in pregnancy before shearing is undertaken.

Environmental controls on lambing rate in Patagonia (Argentina): A regional approach

Sheep herd sustainability in Patagonia is limited by reproductive efficiency. As the herds graze on natural vegetation year round, efficiency is constrained by biophysical factors. Our aim was to characterize the environmental controls over effective lambing rate in northwest Patagonia. We related remotely sensed data [surface temperatures and Normal Difference Vegetation Index (NDVI), a surrogate for forage availability] and climatic information to lambing rates. A spatial model explained 63% of the variability in mean lambing rate, based on mean annual NDVI and mean spring surface temperature. The relative inter-annual variability in lambing rates was of similar magnitude to that of annual NDVI. Both lambing rate and NDVI were less variable than climatic factors. Two regional temporal models explained approximately 25% of the variability, based on NDVI values representative of ewes’ nutrition during late gestation and lambing. These models predicted, with 65% and 76% accuracy respectively, the occurrence of better-than-average and worse-than-average yearly lambing rates. These results provided insights into the factors limiting reproduction, and they form the basis for important decision tools for ranch managers. Prediction of lambing rates based on remotely sensed data will reduce the uncertainty and risk in sheep production, increasing the economic sustainability of sheep production.

Development of baroreflex and endocrine responses to hypotensive stress in newborn foals and lambs

The aims of this study were to compare and contrast the development of the cardiac baroreflex and endocrine responses to acute hypotensive stress in healthy newborn pony foals and lambs during the first two weeks of postnatal life. Under general anaesthesia, seven Welsh pony foals and six Welsh Mountain lambs were catheterised with hind limb artery and vein catheters. Following post-surgical recovery, at 1 week and 2 weeks of age, blood pressures of the animals were raised and lowered acutely by intravenous infusion of phenylephrine and sodium nitroprusside, respectively. During hypotension, blood samples were taken for measurement of plasma hormones associated with activation of the stress axis. Basal arterial blood pressure increased significantly (P<0.05) between week 1 and week 2 in the absence of any significant change in basal heart rate in foals and with a significant reduction in basal heart rate in lambs. In foals, the slope of the heart rate-blood pressure relationship decreased in response to acute hypertension, and it increased in response to acute hypotension, from week 1 to week 2 (all P<0.05). In contrast, in lambs, the slope of the heart rate-blood pressure relationship decreased with both acute hypertension and acute hypotension from week 1 to week 2 (all P<0.05). In foals, there were significant increases in plasma concentrations of noradrenaline, neuropeptide Y (NPY), vasopressin, adrenocorticotrophic hormone (ACTH) and cortisol in response to hypotension (P<0.05). In lambs, there were also significant increases in plasma concentrations of ACTH and cortisol during hypotension. Plasma concentrations of noradrenaline, NPY and vasopressin were not measured during hypotension in lambs. In foals, although the magnitude of the ACTH response to hypotension was smaller at week 2 than week 1, the increment in plasma cortisol was similar in the two age groups. In contrast, in lambs, the profile of both the ACTH and cortisol responses was similar at week 1 and week 2. These data suggest that the increase in basal arterial blood pressure in the foal and the lamb during the first 2 weeks of postnatal life is accompanied by differential maturational changes in the vagal and sympathetic components of the cardiac baroreflex between the two species. These developmental cardiac baroreflex changes occur together with increased adrenocortical responsiveness to acute hypotensive stress, which appears comparatively more mature in lambs than in foals.