Border Leicester × Merino Ewes Research Articles

Mating weight and condition score are both good predictors of lambing potential for young Merino and Border Leicester Merino ewes across different environments and years in Australia

Context Increasing mating weight or condition score increases the lambing potential of ewes (fetuses scanned per 100 ewes joined). Aim We hypothesised that in some years, condition score would contribute an additional effect to mating weight on lambing potential. Methods Border Leicester Merino and Merino ewes were mated naturally to Merino or Terminal rams between 2008 and 2013 at eight linked sites across Australia. Border Leicester Merino ewes were mated in their first year while Merino ewes were not mated until their second year. All ewes were mated for a second time as 2 year olds (Border Leicester Merinos) or 3 year olds (Merino). A total of 4270 Border Leicester Merino and 5788 Merino ewes were weighed and condition scored at mating and scanned for pregnancy. Key results Lambing potential increased by 3.1% per 1 kg increase in mating weight, compared to 1.3% for 1 and 2 year old Border Leicester Merinos respectively, and by 2.1% compared to 1.4% for 2 and 3 year old Merinos respectively (P < 0.05). Lambing potential increased by 27% compared to 13% per increase in condition score for 1 and 2 year old Border Leicester Merinos respectively, and by 29% compared to 25% for for 2 and 3 year old Merinos respectively (P < 0.05). All relationships were linear. When both mating weight and condition score were fitted together, mating condition score explained additional variation to weight in one instance of all the 160 possible breed (n = 2) × age (n = 2) × site (n = 8) × mating year (n = 5) combinations. Conclusions Mating weight and condition score increased the lambing potential of ewes linearly with differences due to ewe age, year and possibly ewe breed. Mating condition score rarely explained additional variation in lambing potential to weight in young Merino or Border Leicester Merino ewes. Implications If ewes are weighed at mating then condition scoring is of minimal extra benefit to predict lambing potential. Achieving the heaviest possible mating weights or highest condition score maximises the lambing potential of ewes in their first two mating years.

Offering maternal composite ewes higher levels of nutrition from mid-pregnancy to lambing results in predictable increases in birthweight, survival and weaning weight of their lambs

Management of nutrition during pregnancy for maternal composite ewes has the potential to improve lamb production and survival in prime lamb production systems but existing condition score (CS) guidelines developed for Merinos may not be appropriate for the optimum production of maternal ewes. To address this, three replicated experiments were conducted at two research sites in Victoria and one in Western Australia. Ewes (781–800 per site) were allocated to four CS treatments following pregnancy scanning (~Day 50) and differentially fed to reach approximate targets of CS 2.4, 2.8, 3.2 and 3.6 by lambing. Single and multiple bearing ewes grazed together, and nutritional treatments were applied until the end of lambing after which ewes and lambs were aggregated into management groups containing all treatments. At lambing, maternal ewe liveweight had a range between treatments of 13.7–19.1 kg (average 16.4 kg) and CS varied by 1.1–1.5 of a CS (average 1.24). Across site analysis indicated that lamb birthweight and weaning weight increased with application of higher CS treatments (P < 0.001). There was also an improvement in survival of multiple born lambs with increasing CS at lambing (P < 0.001). Birthweight was significantly related to survival (P < 0.001) at all sites with no significant effect of birth type on lamb survival. Changes in birthweight and weaning weight could be predicted from ewe joining liveweight, ewe liveweight change to Day 90 and ewe liveweight change Day 90 to lambing. The coefficients derived for each of these effects were similar to those found in previous experiments examining Merino and crossbred Border Leicester Merino ewes. The optimum CS targets for multiple bearing maternal composite ewes may be higher than the industry recommended target for Merino ewes based on advantages in lamb survival and weaning weight.

Crossbred ewes gain more weight and are fatter than Merino ewes when managed together but similar coefficients predict lamb birthweight and survival

Current Australian ewe management guidelines are based on research from Merino ewes and have been transposed to crossbred ewes. It is unknown whether guidelines developed for Merino ewes are applicable to crossbred ewe production systems. To investigate this, the effect of ewe liveweight and condition score profile during pregnancy on lamb birthweight and survival for Border Leicester × Merino (BLM) crossbreds was compared with Merino ewes. Condition score profiles of 720 Merino and 680 BLM ewes were managed from 50 days after ram introduction to achieve one of four target condition scores at lambing. There were three replicates of the four target condition score treatments and both breeds of ewes were in each plot. By Day 140 after rams in, the BLM ewes were fatter (P < 0.001) and heavier (P < 0.001) than the Merino ewes, despite being managed in the same plots. Liveweight at conception and change in liveweight in late pregnancy of the Merino and BLM ewes had a similar effect on the birthweight and weaning weight of their lambs. However, birthweight and weaning weight of lambs from BLM ewes was less sensitive to ewe liveweight change in early pregnancy. Birthweight survival curves were similar in lambs from Merino and multiple-born lambs from BLM ewes, and the survival of lambs from multiple-bearing BLM ewes responded to manipulation of condition score in a similar pattern to lambs from Merino ewes. Therefore, managing liveweight or condition score of multiple-bearing BLM ewes is likely to improve lamb survival in a similar fashion to lambs from Merino ewes, although the absolute response in survival will be smaller than that achieved in Merino ewes at the same condition score. In addition, it is important to manage liveweight of both single and multiple-bearing BLM ewes during pregnancy to optimise weaning weight of their lambs, as those lambs born to BLM ewes of low liveweight were significantly lighter at weaning.

Lifetime Reproductive and Lamb Crop Yields of Fat-tailed Naeemi and Imported Border Leicester Merino Ewes in Intensive System of Production

Local fat-tailed and imported thin-tailed sheep breeds are used for lamb production in hot arid zones. These animals are exposed to an extended summer (seven months) and shorter autumn, winter and spring seasons. The present study examined relative reproductive and lamb crop yields of low and high prolific Naeemi (N) and Border Leicester Merino (BLM) ewes under the intensive management system respectively. Mating systems used were N×N pure breeding and BLM×N rams in three-way crossing. The BLM ewes gave birth to 1.48 lambs per ewe per year as compared to 0.78 lambs per ewe per year for N. The weight of lambs born per ewe was 35% higher and weight weaned 45% higher for BLM ewes compared to N ewes.The lamb mortality was 10% with no significant differences between breeds. The parity significantly (P≤0.05) affected all reproductive traits in both the BLM and the N ewes, except the litter size in N, which was unaffected by parity. The N showed maximum reproduction at second parity (1.08 lambs/ewes) and BLM at third parity (1.63 lambs per ewe). While the lambs from BLM ewes’ first parity showed the highest mortality (21%), lambs from fifth parity showed the lowest mortality (4.5%). The weight of lambs born and weaned was significantly higher (P≤0.05) in autumn-mated than summer-mated BLM ewes. For BLM ewes, mortality was significantly higher (P≤0.05) in summer-born lambs than the lambs born in autumn, winter or spring. This study has demonstrated a moderate lifetime productivity of local N ewes and marked superiority of BLM to N for ewe reproduction and lamb crop yields under the intensive management system.

Milk production and body composition of single-bearing East Friesian × Romney and Border Leicester × Merino ewes

The introduction of East Friesian (EF) genetics into commercial sheep milking herds has the potential to improve milk yield and offer a robust dam for meat lamb production systems. This study was conducted to measure the milk production, feed intake and longitudinal changes in body composition of EF×Romney (EFR) and Border Leicester×Merino (BLM) ewes over the first nine weeks of lactation. Sixteen seconds parity single-bearing EFR (n=8) and BLM (n=8) ewes that had been mated to a purebred EF ram were housed in individual pens from 2 weeks prior to, and until 9 weeks after, lambing and fed a commercial pelleted diet with additional chaff. Milk yield was measured twice a week using the four-hour milking interval technique after injection of oxytocin and body composition was determined by dual energy X-ray absorptiometry (DXA) at 1, 3, 5 and 9 weeks of lactation. Potential milk production was higher in EFR than BLM ewes (2.57 vs. 1.92kg/d, P=0.028) and declined as lactation advanced. Similarly, the yields of milk fat (P=0.015), protein (P=0.018) and lactose (P=0.062) were all higher in EFR than BLM ewes and declined as lactation advanced. Energy intake increased over the first 4 weeks of the study, before reaching a plateau for the remaining 5 weeks of the study. However, there was no significant difference in energy intake or energy balance between EFR and BLM ewes. Changes in tissue energy between DXA scans were highly correlated (R2=0.51, P<0.001) to average estimated energy balance over the same periods. There was no effect of breed on birth weight of lambs nor was there any effect of dam breed on average daily gain of lambs. In conclusion, EFR ewes have greater potential milk yield than BLM ewes but this was not realized as an increased average daily gain in the single lambs possibly due to insufficient milking pressure failing to produce a difference in actual milk yield. It is likely that this difference would be expressed in response to a greater milking demand (i.e. from a milking machine or twin/triplet lambs). The EFR ewes ate more than BLM ewes during lactation and mobilized less fat than BLM ewes to maintain similar nursing lamb growth. However, a greater milking demand of twins or triplets may allow the greater potential milk yield of EFR to be expressed. Alternatively, machine milking EFR would most likely allow the expression of their full milking potential. Finally, DXA was able to predict body tissue mobilization and accretion in lactating ewes and these changes in body composition were related to estimated energy balance indicating that DXA can be used to serially determine body composition in lactating sheep.

Monthly metabolisable energy feed requirements of crossbred ewes in accelerated and traditional lamb production systems

The annual metabolisable energy (ME) feed requirements and patterns of monthly ME requirements for ewe maintenance, gestation, lactation and lamb growth to weaning were evaluated for 1175 crossbred ewes over 4 years at two sites (Cowra and Wagga Wagga). The study involved three lamb production systems: accelerated 8-monthly joinings, with two flocks joined 4 months apart (Ac8), spring joining with an autumn backup joining (SpB), and annual autumn joining (AuA). The Ac8 and SpB systems were evaluated at Cowra and the SpB and AuA systems were evaluated at Wagga Wagga. Two genotypes of ewes, Border Leicester × Merino (BLM) and Hyfer (Dorset × Merino composite), were used at both sites, with natural joinings to Dorset, Suffolk or Hyfer rams. The ewe liveweight, reproduction and lamb production data from individual ewes in the experiment were used to calculate monthly ME requirements using derived simplified equations for ewe maintenance, gestation, lactation and lamb growth to weaning. Annual ME, dry sheep equivalent (DSE = maintenance for a 50-kg, 3.5-year-old ewe = 3030 MJ) and weight of lamb weaned per DSE were analysed and the monthly pattern of ME components presented graphically. The ewes in the Ac8 system had 11% higher ME than those in the SpB system because of their considerably higher annual lambing performance, which resulted in 16–47% greater efficiency of the Ac8 compared with the SpB system when expressed as weight of lamb weaned per DSE. There was also a lower proportion of ME for ewe maintenance in the Ac8 (58%) than SpB or AuA (68%) systems. There was little difference in the annual feed requirements or DSE for ewes in the SpB and AuA production systems, although ewes in the AuA system weaned 9–28% more weight of lamb per DSE than the SpB ewes because of their higher lambing performance. The differences in ME and DSE between the BLM and Hyfer ewes were relatively small and mainly reflected the differences in lambing performance of the genotypes in the various production systems. The seasonal pattern of ME for the AuA and SpB systems showed a sharp increase from the last month of pregnancy to a high peak at weaning with a relatively low requirement for the rest of the year. Under the Ac8 system the ME requirements were more consistent throughout the year and at a lower level than the peak for the other systems. The results highlight the possible increased efficiency from an accelerated lambing system, provided the seasonal feed requirements throughout the year can be provided cost effectively.

Increasing weight gain during pregnancy results in similar increases in lamb birthweights and weaning weights in Merino and non-Merino ewes regardless of sire type

Birthweight is the single largest determinant of survival in lambs and can be predicted from ewe liveweight at conception and liveweight changes during pregnancy. These prediction equations are known for Merino ewes, but it is unknown if they are applicable to non-Merino breeds. We tested the hypothesis that increasing conception weights of ewes will increase the birthweights, survival to weaning and weaning weights of their lambs, irrespective of ewe or sire breed, but that non-Merino lamb birthweights would be less responsive than Merino lamb birthweights, to changes in ewe liveweights during pregnancy. Ewe liveweight, lamb birth and weaning weight records from Merino sires mated to Merino ewes (MM), Border Leicester Merino (Maternal) sires mated to Merino ewes, Poll Dorset or Suffolk (Terminal) sires mated to Merino ewes (TM), and Terminal sires mated to Border Leicester Merino ewes (TMAT) were analysed from the 2007 to 2011 lambings of eight information nucleus flocks. Lamb birthweights increased by 0.032 ± 0.0012 kg from MM ewes and 0.024 ± 0.0026 kg from TMAT ewes with every 1-kg increase in conception weight (P &lt; 0.001). Irrespective of breed, for every 1-kg increase in liveweight change during early and late pregnancy, lamb birthweights increased by 0.021 ± 0.0019 kg and 0.034 ± 0.0019 kg and weaning weights by 0.26 ± 0.013 kg and 0.09 ± 0.011 kg, respectively (P &lt; 0.001). Survival to weaning of single, twin and triplet lambs was highest for lambs from TMAT ewes (89.3% ± 1.25, 84.6% ± 1.49 and 73.4% ± 2.35) and lowest for TM ewes (80.2% ± 1.89, 72.8% ± 2.09 and 57.4% ± 2.98; P &lt; 0.001). Coefficients relating ewe liveweight change during pregnancy to lamb birthweights are similar for Merino and Maternal ewes, however conception weights of Maternal ewes are significantly heavier than Merino ewes when run together, and lamb birthweights from Maternal ewes are less responsive to ewe conception weights. The coefficients reported in this paper will enable development of optimum management guidelines for single-, twin- and triple-bearing Maternal ewes.

Seasonal reproductive performance of crossbred ewes in intensive lamb-production systems

The lambing performance of 1179 crossbred ewes with 5540 joining records in three seasons (autumn, winter and spring) at two sites (Cowra and Wagga Wagga) was evaluated in three lamb-production systems (spring joining with autumn backup matings at both locations, with accelerated lambing at Cowra or annual autumn joining at Wagga Wagga) over 4 years. Two genotypes of ewes, Border Leicester × Merino (BLM) and Hyfer (Dorset × Merino composite), were used at both sites, with natural matings to Dorset, Suffolk or Hyfer rams. The following five traits were analysed separately at each site to evaluate ewe lambing performance: fertility, litter size, lambs born (per ewe joined), lambs weaned (per ewe joined) and weight of lamb weaned (per ewe joined). The mixed model included fixed effects for season of joining, ewe breed, ram group, ewe prejoining weight (spline) and their interactions, with ewe fitted as a random effect. The autumn (February) joinings had higher ewe fertility, litter size and overall lamb production than did joinings in spring (October and November), with winter (June) being intermediate. At the autumn joinings, the BLM ewes had higher fertility, lambs weaned and weight of lamb weaned than did the Hyfer ewes, although this was reversed at the spring joinings, causing significant season × ewe breed interactions. While litter size was larger in the autumn than in the spring for both breeds there was a much smaller seasonal effect among the Hyfer than BLM ewes. Prejoining ewe weight had a significant effect on all reproduction traits, with generally a curvilinear response with increasing weight. The interactions of weight with season × ewe breed were significant (P &lt; 0.001) for all traits at Cowra and most traits at Wagga Wagga. Ram group was significant (P &lt; 0.05) for most traits, with ewes joined to Hyfer rams having higher fertility than those joined to Suffolk. and with Dorset rams being intermediate. At Wagga Wagga, this was the case for spring joinings, but there was no difference between the ram groups in autumn, causing a significant ram × season interaction (P &lt; 0.001). Ewe repeatability ranged from 0.15 to 0.25 for all traits. Using suitable breeds or genotypes, together with optimising management, could improve out-of-season lamb production.

Annual lambing performance of crossbred ewes in out-of-season and accelerated lamb production systems

The average annual lamb production of 1182 crossbred ewes was evaluated in three lamb production systems over 4 years at two sites (Cowra and Wagga Wagga). The lamb production systems were: accelerated 8-monthly joinings with two flocks joined 4 months apart (Ac8), spring joining with an autumn back-up joining (SpB), and annual autumn joining (AuA). The Ac8 and SpB systems were evaluated at Cowra and the SpB and AuA systems were evaluated at Wagga Wagga. Two genotypes of ewes, Border Leicester × Merino (BLM) and Hyfer (Dorset × Merino composite), were used at both sites, with natural joinings to Dorset, Suffolk or Hyfer rams. Four traits were analysed separately at each site to evaluate the average performance per ewe joined per year: number of lambings, number of lambs born, number of lambs weaned and total weight of lamb weaned. Analyses were also undertaken using only spring joining data. At Cowra ewes in the Ac8 system had more lambings (1.23 vs 0.87), lambs born (1.88 vs 1.28), lambs weaned (1.47 vs 1.00) and weight of lamb weaned (31.1 vs 21.5 kg) than ewes in the SpB system (P &lt; 0.01). At Wagga Wagga the AuA system had significantly more lambs born (1.37 vs 1.13), lambs weaned (1.08 vs 0.95) and weight weaned (26.1 vs 21.9 kg) than the SpB system (P &lt; 0.01). The system × breed interaction was significant for all traits because the BLM ewes were greater than Hyfer ewes in the AuA, but the reverse in the SpB system. At both sites the advantage of the back-up joining over only joining in spring was greater for the BLM than the Hyfer ewes. The relative performance of the various lamb production systems for each ewe breed is presented. An accelerated lambing system is likely to be more successful using ewes that have an extended breeding season and good out-of-season breeding performance.

Growth and carcass characteristics of crossbred lambs in various production systems

Lamb growth, carcass and pelt measurements are reported from 5775 lambs born to Border Leicester × Merino (BLM) and Hyfer (Dorset × Merino composite) ewes joined to Dorset, Suffolk and Hyfer rams in three lamb-production systems at Cowra and Wagga Wagga over 5 years. The production systems involved lambings at different seasons of the year and increasing levels of intensification from autumn annual joining, spring joining with a backup mating for non-pregnant ewes, to an accelerated 8-monthly lambing system. Lambs from BLM ewes were 0.7 kg heavier at birth and grew 3% faster and reached slaughter, at 18 kg carcass weight, 1–2 weeks earlier than did lambs from Hyfer ewes (P &lt; 0.01). The advantage in growth rate of lambs from BLM compared with Hyfer ewes was greater for lambs born in November. These lambs had poorer growing conditions over the summer months, with 22% lower growth rate and taking 5 weeks longer to reach slaughter than did lambs born in March or August. There was no difference between Dorset and Suffolk sire breeds for any lamb growth traits, with lambs from Hyfer sires growing 7% slower. Ram and cryptorchid lambs reached slaughter 1 week earlier than did wethers, with ewes a further 9 days later (P &lt; 0.01). Sex differences were maximised when lamb growth was greatest. There were no differences in carcass fat measurements between ram and cryptorchid lambs, although both were considerably leaner than wethers (2.2–3.0 mm fat at the GR site), which were 1.3–2.1 mm leaner than ewes at 18-kg carcass weight. The range in average growth rate of progeny of the BLM ewes from the 12 different source flocks at Cowra and Wagga Wagga was 10–14% of the mean which was twice the difference in average growth rate of progeny from the BLM and Hyfer dams. There was also significant variation among the BLM source flocks for carcass fat measurements. Lamb progeny from the different sire- and dam-breed combinations had varying levels of heterozygosity. There appears to be little loss of heterosis or hybrid vigour for lamb growth, although the sire breed × dam breed interaction was significant (P &lt; 0.01) for age at slaughter at Wagga Wagga, in which the ranking of the lamb types was consistent with the levels of heterozygosity. The estimates of between-lambing repeatability for the ewes were highest for birthweight (0.35 Cowra and 0.27 Wagga Wagga) and declined at later ages (0.26–0.17), with lower estimates for carcass traits.

Genotype and age effects on sheep meat production. 1. Production and growth

The growth, wool production and teeth eruption of animals from five genotypes [Poll Dorsetgrowth (PD) × Border Leicester × Merino (BLM); PDg × Merino (M); Poll Dorsetmuscling (PDm) × M; M × M; BL × M] were evaluated over the age span of 4 to 22 months of age. In total, 16 sires were used to generate the animals and these were selected for growth based on estimated breeding values (EBVs), apart from one group (PDm) which was selected for muscling based on EBVs. In total, 595 animals were slaughtered at 4, 8, 14 or 22 months of age. The birthweight of lambs born to BLM ewes was 0.6 kg heavier (P &lt; 0.001) than those born to Merino ewes, and wether lambs were 0.2 kg heavier than ewe lambs (P &lt; 0.001). The yearling weight (YWT) EBV had no effect on birthweight. There were significant (P &lt; 0.001) differences between genotypes for predicted weaning weight at 4 months of age, with a range of 10.6 kg among the groups. The PDg × BLM were the heaviest (37.8 ± 0.7 kg) and the Merino the lightest (27.3 ± 0.8 kg). Wether lambs were 2.0 kg heavier (P &lt; 0.001) than ewe lambs at weaning. The YWT EBV had no effect on weaning weight. There was a significant (P &lt; 0.001) interaction between the age at slaughter and genotype for final liveweight of each age group. The PDg × BLM were the heaviest at each age and the Merinos the lightest, and for the oldest animals, the BLM were significantly (P &lt; 0.05) heavier than PDm × M, whereas at younger ages this was not the case. The significant interaction (P &lt; 0.001) between sex and age at slaughter reflected the increasing difference in liveweight between the sexes as age at slaughter increased. There was also a significant (P &lt; 0.05) interaction between the YWT EBV and age at slaughter. The overall coefficients were –0.01, 0.14, 0.34 and 0.65 for slaughter ages 4, 8, 14 and 22 months, respectively, indicating that in young animals there was no effect of sire YWT EBV on liveweight, but as the animals aged there was an increasing effect such that progeny of sires with high sire YWT EBV were heavier. This effect was evident within all genotypes. There was a sire breed effect on fleece weight and total wool weight (P &lt; 0.001) with Merino-sired hoggets producing 0.4 kg more wool than Border Leicester-sired hoggets and 1.5 kg more than Poll Dorset-sired hoggets. There was a weak genotype effect on time to erupt the first permanent incisor, which if modelled as a proportion of Border Leicester (0, 1/4, 1/2) was significant (–34 ± 12 days, P &lt; 0.05), Border Leicester earlier than not Border Leicester. Ewe lambs took 9 days longer (P &lt; 0.05) to erupt their first permanent incisor compared with wether lambs.

Acute exercise stress and electrical stimulation influence the consumer perception of sheep meat eating quality and objective quality traits

The effects of acute exercise stress and electrical stimulation on lamb eating quality and objective measurements of quality were evaluated on the Longissimus thoracis et lumborum (LTL) and the Gluteus medius (GM) muscles. Meat quality attributes were also assessed on the LTL, Semimembranosus (SM) and the Semispinalis capitis (SC) muscles. Forty-eight Poll Dorset × Border Leicester–Merino ewes of about 6 months old were randomly allocated to treatments in a 2 × 2 factorial design, with the respective factors being exercise (Ex, 0 v. 15 min) and post-slaughter low voltage electrical stimulation (control v. ES). In general, exercise reduced the rate of pH fall and increased the ultimate pH of all 3 muscles (P&lt;0.05). This effect was more pronounced in the SM than in the LTL and SC. Exercised LTL and SM muscles also had lower surface lightness (L*) values and higher muscle total water content, indicating an increased incidence of dark cutting meat. Exercised LTL steaks were rated higher for tenderness and juiciness by the taste panelists and had lower Warner-Bratzler shear force values, as is often observed with high ultimate pH meat. Electrical stimulation reduced initial pH (pH0.5) values, but resulted in a slower rate of pH fall in the LTL and SM thereafter. Electrical stimulation resulted in an elevation of temperature at rigor in the SM by 10°C (15 v. 25°C) and in the LTL by 3.1°C (7.4 v. 10.5°C). While no effect of electrical stimulation was observed with instrumental analysis, electrical stimulation reduced sensory tenderness scores and overall liking for the GM, and tended to reduce flavour and juiciness of both the GM and LTL. In conclusion, acute exercise pre-slaughter improved eating quality, but caused dark cutting meat. The negative effect of low voltage stimulation on the eating quality of the GM was probably due to a high rigor temperature and associated heat toughening.

Birth weights, meningeal lesions, and survival of diverse genotypes of lambs from Merino and crossbred ewes

The survival of 3530 lambs of 6 diverse genotypes (Poll Dorset, Texel, Border Leicester, and Merino sires) from Merino and Border Leicester Merino ewes was studied over 3 years at Cowra in New South Wales. Some of the matings involved laparoscopic insemination, which allowed gestation length to be recorded. Each mating group lambed in separate, adjacent paddocks, and birth weights, gestation length, lamb survival, and lamb autopsy data were collected. Breed of ewe significantly affected birth weight and gestation length. Lambs from Merino ewes were 0.3 kg lighter than those from Border Leicester Merino ewes and had a 2 days longer gestation. Both birth weight and gestation length varied significantly between years. Lamb losses to 3 days post partum were 11.3%, 20.8%, and 46.2% for singles, twins, and triplets, respectively. Meningeal lesions and presentation difficulties were associated with 66.6% of all deaths. The high incidence of lesions contrasts with a negligible incidence in some reports involving lean ewes and it is concluded that fatness of ewe may be implicated.

Lamb production from diverse genotypes. 1. Lamb growth and survival and ewe performance

AbstractGrowth and survival of 3673 female and cryptorchid lambs representing the range of types (second cross, first cross and Merino) produced in the Australian lamb industry are reported. The lambs were sired by a selection of Poll Dorset (D; no. = 7), Texel (T; no. = 10), Border Leicester (BL; no. = 12) and Merino (M; no. = 12) rams and born to Border Leicester × Merino (BLM) and Merino (M) dams, which resulted in six lamb genotypes (D×BLM, T×BLM, D×M, T×M, BL×M and M×M). The second cross lambs (D×BLM, T×BLM) were heavier at birth, weaning and post-weaning and had higher growth rates, than first cross lambs (D×M, T×M, BL×M), which were higher than M×M lambs (P&lt; 0·01). For post-weaning weight (cryptorchids at 156 days) second cross lambs were 4·2 (s.e. 0·3) kg heavier than comparable sired first cross lambs, with the BL×M 2·6 (s.e. 0·5) kg lighter than other first cross types and the MxM a further 4·2 (s.e. 0·6) kg lighter. The average advantage of D over T crosses was 1·0 kg for post-weaning weight, with greater variation amongst individual sires.Lamb survival to weaning was 76% and it was affected by birth weight and birth type (P&lt; 0·01). Sire breed had no significant effect on lamb survival, whereas lambs from BLM ewes had higher survival than those from M ewes (P&lt; 0·01).Overall the proportion of ewes lambing was 84% with a mean litter size of 1·77. There was no difference infertility between AI (thawed frozen semen and laparoscopic insemination) and natural (single sire) mating, although the M were higher than the BLM ewes (P&lt; 0·01). Gestation length was 2·3 days shorter (P&lt; 0·01) for BLM than M ewes and there was no difference between D and T sire breeds. There was little effect of birth type on gestation length but it increased with birth weight within birth type categories. Between year repeatability of gestation length for ewes was 0·33 (s.e. 0·05).

Diverse lamb genotypes—2. Meat pH, colour and tenderness

The effect of genotype on meat ultimate pH, colour and tenderness was studied in 3 experiments involving 436 lambs. The lambs were sired by a selection of Texel (T), Poll Dorset (PD), Border Leicester (BL) and Merino (M) rams, crossed with Border Leicester × Merino (BLM) and Merino (M) ewes giving 6 genotypes (T × BLM, PD × BLM, T × M, PD × M, BLM and M × M). In experiment 1, pH data were obtained for 4 muscles ( M. Semimembranosus (SM), M. Biceps femoris M. Semitendinosus and M. Longissimius thoracis et lumborum (LL)) from 198 carcasses representing two sexes (104 cryptorchid males, 94 ewes). There were significant differences for pH between genotypes in both sex groups. BL × M and M × M lambs tended to have higher pH values than the other genotypes. In experiment 2, meat pH, colour using a chromameter, and tenderness data were obtained for 186 lambs representing two sexes (101 cryptorchid males, 85 ewes). There were few significant differences between genotypes for the various meat quality traits amongst the ewes. The PD × BLM ewes had a significantly lower ( p < 0.05) pH than the BL × M ewes for the LL and SM muscles. The BL × M crypt orchids had a higher LL muscle pH ( p < 0.05) than the PD × BLM cryptorchids with other genotypes being intermediate. There were no significant differences between the genotypes for muscle shear force values. Within experiment 2, LL samples were taken from an additional 52 cryptorchid carcasses these being from 3 specific Poll Dorset sires (experiment 3). One of these sires (sire 3) was suspected of carrying a gene for increased muscling. Sire had a significant effect ( p < 0.05) on shear force values, cooking loss and L ∗ colour values, but not a ∗ or b ∗ colour values or pH. Sire 3 progeny had significantly ( p < 0.001) tougher LL muscles than those from the other 2 sires. Sire 3 also had the lowest L ∗ values, but was intermediate for cooking loss. There was no significant sire effect on LL area at the same carcass weight, but boneless loins from the progeny of Sire 3 were significantly ( p < 0.05) heavier. In a fourth experiment, meat colour was measured at three sites (LL, diaphragm and M. Obliquus externus abdominis) on 86 cryptorchid carcasses 24 hr post-mortem. There was little association between L ∗, a ∗ and b ∗ values measured at the different sites.

Assessing Wiltshire Horn-Merino crosses. 3. The 50% Wiltshire Horn as a prime lamb producer

Wiltshire Horn-Merino (WH-M) and Border Leicester-Merino (BL-M) ewes, both with 50% Merino ancestry, were mated in late spring to lamb in 1985 and 1986 to either Dorset Horn (DH) or WH-M rams. Lambs from WH-M sires grew more slowly than lambs from DH sires, by 2 to 13% depending on dam breed and age of lamb. Lambs from WH-M dams grew 3 4 % slower than lambs from BL-M dams in 1985, a year of good pasture and with only DH rams used. In the following year, they grew at a similar rate from birth to weaning if from DH sires, but 11% more slowly if by WH-M sires. From weaning to turnoff, the ranking was reversed, with lambs from WH-M dams growing 11% faster, and sire breed not significant. When mated to DH rams, both the WH-M and BL-M ewes produced lambs with similar dressing percentages and fat depths over the 12th rib. Lambs sired by WH-M rams were leaner than those sired by DH rams, particularly for single-born lambs. The WH-M ewes tended to have a higher percentage of lambs marked per ewe joined than the BL-M ewes, but the advantage was not statistically significant. The difference was mainly due to fewer barren ewes, but the WH-M ewes also showed slightly higher prolificacy. The WH-M ewe shows good fertility and prolificacy, and when mated to a DH ram gives lambs with growth and carcase characteristics very similar to a BL-M identically mated. Mated to a WH-M ram, it gives slower growth but leaner carcases capable of being efficiently grown to heavier liveweights than conventional Australian 3-breed crosses.

Circadian rhythm in wool depilation force in Merino and Merino X Border Leicester sheep

SummaryAs part of an ongoing investigation of ovine neuroendocrine mechanisms relating to photoperiod and eventually to wool growth, the diurnal variation of depilation force (an index of the strength of attachment of wool fibres to the skin of sheep) was investigated in Merino wethers and Border Leicester Merino ewes. Circadian rhythms were demonstrated in depilation force in both ewes and wethers. Further experiments were performed to investigate circadian endocrine rhythms which may have some bearing on the observed rhythm in depilation force. Circadian rhythms 180° out of phase with the depilation force rhythm were observed in plasma cortisol concentrations and in pineal serotonin N-acetyltransferase activities in Merino wethers.