Lamb Weaning Research Articles

Preliminary genetic correlations of milk production and milk composition with reproduction, growth, wool traits and worm resistance in crossbred ewes

Genetic correlations were estimated between ewe milk production and composition traits and other production traits, including early growth, wool, worm resistance and reproduction, among 944 crossbred ewes. Daily milk production of the ewes was estimated using the 4-h machine milking test procedure at approximately 3, 4 and 12 weeks of lactation, with milk composition assessed by sampling for fat %, protein % and lactose % at each milking. The ewes were the progeny of 74 maternal breed sires and mainly Merino dams and 77% of the ewes were milked on their first lactation. The production traits included pre-weaning and post-weaning growth rate of the ewes, their yearling wool production, clean yield and fibre diameter and worm egg count. The ewes were joined naturally to meat rams over 3 years, resulting in 2432 reproduction records. Ewe reproduction traits included: litter size (LS), rearing ability (RA) or lamb survival, number of lambs weaned (NLW) and average lamb weaning weight in the litter (AWW). Genetic correlations were estimated by bivariate mixed models using ASREML. The genetic correlations between milk yield and growth rates of the ewes were moderate and positive (0.38–0.49) with standard errors of about 0.3. The genetic correlations between the milk composition traits and growth traits were variable and generally similar to or smaller than their standard errors, except for lactose% and post-weaning gain (0.58). Estimates of the genetic correlations between milk yield and the wool traits and worm resistance were generally low and smaller than their standard errors. Lactose% was moderately positively correlated with the wool traits (0.19–0.51). The phenotypic correlations between all the milk traits and the ewe growth, wool and worm resistance traits were close to zero. The genetic correlations between milk yield and LS and NLW were moderate and positive (0.50–0.59), with the genetic correlation between milk yield and AWW being slightly lower (0.44) and RA close to zero. The phenotypic correlations between milk yield and the reproduction traits were all small and positive. The genetic correlations between the milk composition traits and reproduction traits were variable and all less than their standard errors. The corresponding phenotypic correlations were all close to zero. The genetic correlations in this study provide preliminary estimates of the parameters required for more accurate genetic evaluation and the development of breeding programs incorporating meat and wool objectives that include ewe reproduction and milk production.

Genetic correlations between early growth and wool production of crossbred ewes and their subsequent reproduction

Genetic correlations between reproductive and productivity traits of ewes and their early growth, wool production and worm resistance traits were estimated among 2460 crossbred ewes. The ewes were progeny of 74 maternal breed sires and mainly Merino dams. The ewes were born over 3 years and had three joinings with a total of 6824 ewe joining records. The reproductive and ewe productivity traits included: (i) fertility (ewes lambing per ewe joined); (ii) litter size (number of lambs born per ewe lambing); (iii) rearing ability or lamb survival (lambs weaned of lambs born for lambing ewes); (iv) number of lambs born (NLBj) per ewe joined; (v) number of lambs weaned (NLWj) per ewe joined; (vi) total litter weight weaned (TWWj) per ewe joined; and (vii) the component trait average lamb weaning weight in the litter (AWW). The growth traits included the weight of the ewe at birth (BWT), weaning (WWT) and postweaning (PWWT), as well as growth rate pre- and postweaning. The wool traits included greasy (GFW) and clean fleece weight (CFW), yield and average fibre diameter (FD) at their first adult shearing. Worm egg count (WEC) during their first year was also recorded. Bivariate mixed models analyses using ASReml procedures were used to estimate the genetic correlations. The genetic correlations between TWWj and growth traits were positive and moderate to high and ranged from 0.34 for BWT to 0.61 for PWWT. Those for the other composite reproductive traits were slightly lower and ranged from 0.27 to 0.54 for NLWj and from 0.07 to 0.46 for NLBj. The genetic correlations between the overall measures of reproduction (NLBj, NLWj and TWWj) and GFW, CFW and FD were negative and generally low to moderate (–0.21 to –0.52). The correlations were generally larger for NLBj than for NLWj and TWWj. The genetic correlations between the reproductive traits and WEC were close to zero, except between AWW and WEC (0.42). The phenotypic correlations between the reproductive traits and the growth, wool and WEC traits were all close to zero. The genetic correlations were generally favourable between ewe reproduction and growth, with early selection for traits such as WWT and PWWT likely to give some improvement in subsequent reproduction and ewe productivity. In contrast, there appears to be a slight antagonism between reproduction and wool production. This study provides estimates of genetic correlations from crossbred ewes that add to the limited knowledge of these parameters that will improve the accuracy of genetic evaluation and prediction of the outcomes from breeding programs for meat and wool objectives that include reproduction.

Effects of shearing at housing, grass silage feed value and extended grazing herbage allowance on ewe and subsequent lamb performance

The study involved 120 crossbred ewes (sixty 1.5 years old animals and sixty 2.5 years old animals; initial liveweight 67.6 kg, condition score 3.7), that were mated in October. They were assigned to six treatments (two shearing treatments (shorn and unshorn) × two silage feed values (low and medium) and two extended grazed herbage allowances (1.0 and 1.8 kg dry matter (DM)/day)) designed to evaluate the effects of shearing at housing, grass silage feed value and extended-grazed herbage allowance on their performance and the performance of their progeny. Swards, which had silage harvested on 6 September, received fertiliser N (34 kg/ha) for extended (deferred) grazing between 19 December and lambing in mid-March. The herbage was allocated at DM allowances of 1.0 or 1.8 kg/ewe daily until 1 February. For the final 6 weeks of pregnancy, daily herbage DM allowances were 1.5, 1.6, 2.0, 2.0 and 2.0 kg for weeks 6, 5, 4, 3 and 2 to parturition, respectively. Two grass silages (low and medium feed value) were offered from housing on 19 December to lambing in mid-March. At housing, half the ewes were shorn whilst the remainder remained unshorn. Each ewe received 23.4 kg concentrate prior to lambing. For the extended-grazed herbage and the low and medium feed-value silages, DM concentrations were 132, 225 and 265 g/kg, and metabolisable energy (ME) concentrations were 10.0, 10.0 and 10.7 MJ/kg DM, respectively. Treatment did not alter (P > 0.05) litter size or number reared. Grass silage feed value did not significantly alter silage DM intake, or ewe and subsequent lamb performance. Increasing herbage allowance in mid-pregnancy decreased herbage utilisation (P < 0.05) and increased herbage intake (P < 0.05). Shearing increased silage intake (P < 0.05), lamb birth weight (P < 0.01) and tended to increase lamb weaning weight (P = 0.07). Relative to the housed shorn ewes, extended grazing did not alter (P > 0.05) ewe or subsequent lamb performance. It is concluded that shearing ewes at housing increased lamb birth weight due to increased silage intake probably associated with cold stress immediately post shearing and reduced heat stress in late pregnancy. Based on differences in lamb weight at weaning 0.8 kg of grass silage DM intake had the same feed value as a daily extended herbage DM allowance of 1.8 kg per ewe throughout the study. Neither silage feed value nor herbage allowance in mid-pregnancy affected lamb birth weight or subsequent growth rate.

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

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

Influence of space allowance and housing conditions on the welfare, immune response and production performance of dairy ewes

The experiment used 45 Comisana ewes, divided into 3 groups of 15. The aim was to determine the effects of two different stocking densities and two different housing conditions on welfare, and on production performance of dairy ewes. The stocking densities tested were: high stocking density (1 x 5 m2/ewe, HD group) and low stocking density (3 m2/ewe, LD group); the two housing conditions tested were: ewes housed indoors (LD group, 3 m2/ewe) and ewes allowed to use an outdoor area (LDP group, 3 m2/ewe divided into 1 x 5 m2/ewe indoors and 1 x 5 m2/ewe outdoors). At the beginning of the experiment, and then every 2 months, the cell-mediated immune status of sheep was evaluated. One month after the beginning of the experiment, and 20 d later, the ewes were injected with chicken egg albumin (OVA) to assess their humoural immune responses. Starting from the beginning of the experiment and then monthly, behavioural activities of ewes were monitored using 15-min scans. After lamb weaning, milk yield from individual ewes was measured and milk composition analysed weekly. Housing conditions (low density reared ewes indoors v. low density reared ewes with free access to an outdoor area) affected cell-mediated response, which was higher in LDP than in LD ewes. Concentrations of anti-OVA IgG were mainly influenced by space allowance, with higher antibody titres in LD than in HD ewes throughout the experiment. Both housing conditions and space allowance affected sheep behavioural activities: a greater proportion of LDP ewes displayed standing and drinking behaviours than LD ewes, and a greater proportion of LD ewes was observed walking than HD ewes. Ewes allowed access to the outdoor area had a higher protein content and lower somatic cell count in their milk, whereas reduced space allowance led to a reduction in milk yield and an increase in somatic cell count of milk. Results indicate that both increased space allowance and availability of outdoor area can improve the welfare and production performance of the lactating ewe.

Risk factors and impacts of clinical and subclinical mastitis in commercial meat-producing sheep flocks in Quebec, Canada

We conducted a prospective observational study on clinical and subclinical mastitis in 30 commercial meat-producing sheep flocks from 2 regions of the province of Quebec, Canada. A total of 2792 ewes selected in late gestation were followed from lambing to weaning of lambs. The incidence of clinical mastitis for the total lactation period (average of 58 days) ranged among flocks from 0 to 6.6%, with a median of 1.2%. The most frequently isolated bacteria from the cases of clinical mastitis, in pure or mixed culture, were Mannheimia haemolytica (26%), Staphylococcus aureus (23%), and coagulase-negative staphylococci (17%). Incidence of clinical mastitis was higher in ewes that gave birth to 3 or more lambs and from the Estrie region, and was associated with an increase in ewe mortality, an increase in lamb mortality at the litter level, and a decrease in lamb's weaning weight for lambs born in multiple litter size or from ewes ≥4 years old. Among 354 selected ewes with clinically normal udder at the end of lactation, 28.8% had potentially pathogenic bacteria isolated from milk. The most prevalent bacteria were S. aureus (9.3%) and coagulase-negative staphylococci (9.3%). The risk of having a positive culture in at least one half was different between the two regions. Prevalence of ewes ( n = 261) with California Mastitis Test (CMT) positive result in at least one half was 24.1 and 14.9% using a cut-off of ≥1+ and ≥2+, respectively. Prevalence of culture-positive udder halves was 11.7% for CMT-negative compared with 53.6% for CMT 3+ halves. CMT status was positively associated with the isolation of coagulase-negative staphylococci, M. haemolytica, S. aureus, and various Streptococcus species, but not with other isolated bacteria. Additionally, prevalence of CMT-positive halves was higher in ewes from the Estrie region, aged of ≥4 years versus 1 year, having clinical mastitis previously detected in the lactation and/or with low body condition score. Lamb weaning weight was associated with CMT status of ewes, while weaning weight was not associated with milk culture results. More research is needed to understand the dynamic of milk SCC and IMI in ewes from meat-producing flocks, its economical impact and best ways to control it.

Vegetation dynamics and livestock performance in system-scale studies of sheep and cattle grazing on degraded upland wet heath

Upland wet heaths in the UK are of international conservation significance but high grazing pressure by sheep has caused widespread degradation. Restoration by reducing sheep numbers is not always successful if competitive grasses such as Molinia caerulea become dominant. Cattle can reduce grass biomass but their utility as a conservation tool is also dependent on economic viability. This study assessed the effect of two sheep-only and two mixed cattle-plus-sheep grazing regimes on vegetation and livestock performance over 4 years at a system scale on a 103 ha heterogeneous degraded wet heath. Grazing regimes were sheep all year at 1.5 or 0.66 ewes ha −1 with 25% removed in winter, with or without dry Continental cross suckler cows at 0.75 cows ha −1 for up to 10 weeks in summer. In mixed grazing paddocks, M. caerulea cover declined substantially in vegetation types where it was abundant. Calluna vulgaris declined slightly in the mixed grazing paddocks, primarily because of localised trampling. M. caerulea increased in the sheep-only paddocks and C. vulgaris declined slightly despite low grazing indices. Other changes in plant community composition were minor. Cow daily liveweight gains were adequate to regain body condition prior to calving, but these and ewe mating weights and lamb weaning weights were lower in paddocks with 1.5 than 0.66 ewes ha −1. Ewe and lamb performance were similar in mixed and sheep-only paddocks at each ewe stocking rate. Cows can be grazed with sheep to remove M. caerulea biomass without detriment to livestock performance, although the stocking levels used in this study would not be sustainable every year. Despite reduction of M. caerulea biomass, there was no evidence that heathland vegetation was being restored after 4 years. Restoration by grazing alone probably requires longer timescales and agri-environment schemes should avoid prescribing stocking levels regardless of livestock species.

Comparative study between sheep and goats on rumenic acid and vaccenic acid in milk fat under the same dietary treatments

A number of studies have shown that the rumenic acid (RA = cis-9 trans-11 C 18:2 CLA) content of milk fat is usually higher in sheep than in goats, due partly to different dietary regimens. An experiment was conducted with 12 lactating dairy ewes and 12 goats with the objective to compare the two animal species (sheep/goats) fed diet with the same forage/concentrate ( F/ C) ratio, on their milk fatty acids (FA) profile with emphasis on RA and vaccenic acid (VA) production. The experiment was carried out in three consecutive phases, lasted 3 weeks each, immediately after weaning of lambs and kids. In phase I, the ewes and the goats were fed according to their maintenance and lactation requirements, with 14 kg alfalfa hay, 4 kg wheat straw and 12 kg concentrate the 12 ewes ( F/ C ratio = 60/40), and with 14 kg alfalfa hay, 4 kg straw and 24 kg concentrate the 12 goats ( F/ C ratio = 43/57). In phase II, 14 kg alfalfa hay, 4 kg straw and 14 kg concentrate were offered daily to each group of sheep and goats, with a F/ C ratio = 56/44. In phase III, all ewes and goats were fed individually with 0.8 kg alfalfa hay, 0.2 kg wheat straw and 0.8 kg concentrate daily with a F/ C ratio = 56/44. The results showed that the different F/ C ratio between sheep and goats diets, in phase I, changed significantly the milk FA profile, with no significant difference in RA and VA milk fat content between sheep and goats in phase I. In phases II (group feeding) and III (individual feeding), where sheep and goats fed with the same amount of food of the same F/ C ratio, the sheep milk fat had higher RA and VA content compared to goats. In conclusion, these findings support the hypothesis that there are species differences, as RA and VA production concerns, which needs further investigation.

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

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

Histological and Ultrasonographic Monitoring of Folliculogenesis in Puerperal Ewes after Spring Lambing

The time of the first ovulation depends on the sheep breed, feeding conditions, year season, length of lamb nursing and following galactopoiesis. The objective of the present study was to analyse the follicle status after parturition in non-lactating Improved Valachian ewes. Laparotomy with following ovariectomy was performed after lamb weaning (spring) on days 17, 24 and 32 after parturition. The ovaries were USG analysed with 5.0 MHz linear and 7.5 MHz convex transducer. Follicular data were analysed quantitatively and qualitatively. The ovaries were collected at the end of laparotomy and fixed in 10% formalin. The sections of the ovarian tissue were stained with haematoxylin and eosin and Azan staining. Ovarian slides were microscopically studied and analysed by LUCIA-G ver. 4.71. The differences in the ovary size were not significant. The number of follicles &lt; 3 mm monitored by USG on day 32 was higher than that on day 17 after parturition. The image analysis of the ovary sections showed significantly higher numbers in the total follicles (P &lt; 0.05) and the follicles &gt; 3 mm (P &lt; 0.001). The rate of atresia was 82% and 89% on day 17 and on day 32 post partum, respectively. We observed single ovulation on day 17 and double ovulations on days 24 and 32 post partum. More than half of the total number of antral follicles visible on the ovary surface was prepared for recruitment and this number was higher on day 32 post partum. Follicle selection connected with a relatively low rate of atresia and responsible preovulatory follicle sizes opened the way for selecting more follicles for the dominance process and thus also for the occurrence of double ovulations.

Effects of weaning lambs in two stages or by abrupt separation on their behavior and growth rate

A study was conducted to evaluate effects of age at weaning in combination with different weaning procedures on 2 breeds of lambs (Merinoland, Rhoenschaf). Lambs were either weaned at 8 or 16 wk of age in 2 stages or with the traditional method of weaning by abrupt separation. In the 2-stage treatment, lambs were prevented from nursing their dam for 1 wk (stage 1) before their separation (stage 2). Control animals were nursed by their dams until they were separated. Lamb BW and behavior (vocalization, agitation) were recorded before and after separation. After separation, lambs weaned at 8 wk of age had greater (P = 0.004) ADG compared with lambs weaned at 16 wk of age. Control lambs had greater (P < 0.001) agitation scores [1 = no agitation (normal behavior; i.e., feeding, resting, lying, standing, or play behavior) to 3 = high agitation (continuously moving, restlessness, or vocalization)] irrespective of weaning age and breed. On the day of separation, 2-stage lambs had scores from 1.17 to 1.35, whereas control lambs were scored from 1.70 to 1.79. After separation, lambs weaned in 2 stages vocalized up to 98.2% less (P = 0.001) than control animals. Furthermore, bleats were greater for Rhoenschaf lambs and at a weaning age of 8 wk (P < 0.05). Differences between treatments were greatest on the day of separation. Vocalization decreased continuously within the first 3 d of weaning to zero. Lambs weaned in 2 stages were less distressed than lambs weaned by the traditional method of abrupt separation based on behavioral data, but ADG until 12 and 16 wk of age did not differ (P > 0.05) for either treatment in this study.

Genotype by environment interaction for lamb weaning weight in two Norwegian sheep breeds1

Genotype x environment interaction (G x E) effects on live weaning weights of lambs were studied by using the 2 breeds Norwegian White sheep (NWS; heavy, long-tailed) and Spel sheep (Spel; lighter, short-tailed) as genetic groups (G). A total of 37,338 NWS lambs and 30,075 Spel lambs born from 1989 to 1999 on 40 farms that kept both breeds together were included in the analyses. Environment was characterized by farm x year (E). In a mixed linear model framework, significance of the random G x E effect and breed-specific environmental variances were tested by using a log-likelihood approach. Directions and magnitudes of the effect were described through variance component estimates. An across-genotype environmental correlation was also used. There was a significant G x E effect on lamb BW; significant breed differences were found for variance of flock x year effects, indicating different phenotypic plasticities with changing flock x year environments, with the NWS being more sensitive to environmental change. Further, the breed-specific residual variance was greater for NWS, indicating that the effects of environmental variation were larger for the weaning weights of the NWS breed within flock and year. Further, the correlation between flock x year effects for the 2 breeds was significantly different from unity (0.82 +/- 0.02), indicating that the common environment is "perceived" differently in the 2 breeds. The best environment for one breed is not necessarily best for the other breed, and vice versa. Solutions of flock x year effects may be used to describe how environmental characteristics such as climate and topography affect the production of different genotypes, and for clustering of environments, thus facilitating improvement of breeding programs and management schemes for domestic and wild ungulate populations.

Potential for Early Breeding of Kivircik (Western Thrace) Ewes

Koyuncu, M., KaraUzun, S. and Ozis, S. 2007. Potential for early breeding of Kivircik (Western Thrace) ewes. J. Appl. Anim. Res., 32: 61–64. This study was carried out to investigate the possibility of early breeding of ewe lambs in Kivircik sheep breed. Mating and reproduction performances were investigated in normally mated (15–16 months old) and early mated (7 months old) females. The rates of pregnancy, lambing, single birth, survival up to weaning, the number of lambs born per ewe lambing and the number of the weaning lambs per ewe lambed were found as 78.33 and 94.33%, 78.33 and 94.33%, 91.49 and 89.00%, 90.20 and 96.67%, 1.09 and 1.20, 0.98 and 1.16, respectively, in early and normally mated ewes. Though early breeding resulted in lower fertility, twinning and lambs born and weaned per ewe lambed, saving of eight months is an important factor to recommend early mating.

The effect of breeding ewe lambs on subsequent two-year-old ewe performance

This study was undertaken to determine if breeding ewe lambs (hoggets) would influence subsequent two-year-old (two-tooth) ewe liveweight and reproductive performance and their lamb's performance to weaning. Two-tooth Romney ewes that had been bred and lambed as a hogget (n=505) were compared with those of 196 ewes that were bred as a hogget but did not lamb and 235 ewes that were not presented for breeding as a hogget. Hogget lambing resulted in reduced (P<0.05) two-tooth liveweight and body condition score at breeding although still present this liveweight difference was reduced by two-tooth lamb weaning. Two-tooth ewes that had previously lambed as a hogget had greater (P<0.05) returns to service rates and lower (P<0.05) fecundity (multiple-bearing/two-tooth bred) than those that were bred for the first time. Two-tooth lamb liveweights were unaffected by hogget lambing. These results show that hogget lambing had a small negative effect on subsequent two-tooth reproductive performance. This was most likely caused by reduced liveweight at two-tooth breeding and indicates that farmers need to ensure management practices are in place to reduce the impact of hogget lambing on two-tooth liveweight.

Effects of housing conditions on the welfare of lactating ewes

Space allocation and housing conditions are critical factors for health and welfare of housed animals and it is well known that sheep are less easily accustomed to confinement than other farmed animals. This study was undertaken to investigate changes in the behavioral, immune and production performances of lactating ewes when subjected to different housing conditions. A one-year trial (from May 2005 to May 2006) was performed with 45 Comisana ewes. At the beginning of the trial the ewes were divided into three groups of 15 each, which were separately penned in the same building and balanced in terms of age, body weights and time of lambing. The treatments were: i) high stock density (HD) with individual ewe having 1.5 m2, ii) low stock density (LD) with individual ewe having 3 m2, iii) low stock density with external paddock (LDP) with individual ewe having 3 m2 divided into 1.5 m2 inside the building and 1.5 m2 in the external paddock. The cell-mediated immune status of sheep was evaluated by means of skin-tests which were performed on all the animals at the beginning of the trial, and then during the dry period, the first phase of pregnancy, the transition period and the beginning of lactation. Chicken egg albumin (OVA) was injected subcutaneously in both shoulders of each ewe to assess the humoral immune response. Antibody titers to OVA were determined in blood samples collected immediately before the first antigen injection and then at 20, 40, 60 and 80 days of the study period by an ELISA performed in 96-well U-bottomed microtiter plates. Behavioral observations were recorded once monthly by two trained observers equipped with video cameras. Scan samples were taken every 15 min from 0830 to 1230 and from 1330 to 1730. After lambing and weaning of lambs, the ewes were machine milked twice daily and milk yield was recorded daily by means of graduated measuring cylinders. Milk samples, consisting of proportional volumes of morning and evening milk, were individually collected weekly in 200 ml sterile plastic containers after cleaning and disinfection of teats (70% ethyl alcohol) and discharging the first streams of foremilk. Samples were carried to our laboratory by means of transport tankers at 4 °C, and analyzed for their chemical composition. Data were processed by analysis of variance, using the GLM procedure of SAS. Cell mediated immune responses detected in LDP ewes were higher than LD responses (P < 0.001). Mean antibody concentration was higher in LDP ewes than in LD ewes (P < 0.05), and in LD than in HD ewes (P < 0.001). A higher number of LDP ewes was observed standing and drinking than LD ewes (P < 0.001 and P < 0.01, respectively). Higher proportions of LD than HD ewes were observed in ambulatory activity (P < 0.01). On the contrary, lower proportions of LD than HD were observed drinking (P < 0.01); a tendency in higher number of aggressive activities was recorded in HD than in LD ewes (P < 0.1). Milk yield was lower in HD than in LD ewes (P < 0.05); milk from HD animals displayed and Somatic Cell Count (SCC) than milk from LD ewes (P < 0.001 and P < 0.05, respectively). Milk from LDP ewes had higher protein and whey protein contents (P < 0.05), and contained more lactose and less SCC than milk from LD ewes (P<0.01 e P<0.05, respectively). Data from the present trial showed that a stocking density of 1.5 m2/animal negatively influenced ewe welfare and production performance.

A preliminary genetic analysis of breech and tail traits with the aim of improving the welfare of sheep

The area of naturally bare skin around the perineum was scored at weaning in lambs (n = 2152) from a composite flock of New Zealand crossbred sheep. Breech bareness was scored on a range from 1, where wool was growing right to the edges of the anus, to 5, where a large bare area surrounded the perineum. Bareness on the under surface of the tail was measured on a linear scale at tail docking. Dag score (degree of breech soiling) was recorded at weaning, on a scale of 0–5, where an increasing score indicated more dags. Dag score was taken as a measure of the risk of flystrike in the breech. Female lambs tended to have slightly greater (P &lt; 0.001) breech bareness score (mean score 2.7) than males (mean score 2.6), whereas mean dag score of females was lower than that of males (0.45 v. 0.53; P &lt; 0.05). Breech bareness score had a heritability of 0.33 ± 0.06, and the length of bare skin under the tail had a heritability of 0.59 ± 0.06. The genetic correlation between breech bareness score at weaning and length of bare skin under the tail at docking was positive (0.35 ± 0.10). These 2 traits had phenotypic correlations with dag score of –0.17 ± 0.02 and –0.03 ± 0.03, respectively, and genetic correlations with dag score of –0.30 ± 0.13 and 0.03 ± 0.12, respectively; negative values indicated a favourable relationship. Tails were removed at docking, so the phenotypic correlation of about zero between tail data and dag score at weaning was of little utility. Our results suggest that selecting for these 2 bareness traits could reduce dag formation and the associated risk of breech strike.

The relationship of lamb growth from birth to weaning and the milk production of their primiparous crossbred dams

The growth rate of 667 single cross lambs from birth to 4 weeks (Period 1) and 4 weeks to weaning at 12 weeks (Period 2) was measured, along with the milk production of their 520 primiparous crossbred ewe dams over 3 years. The lambs were the progeny of Poll Dorset rams and first cross ewes lambing for the first time at 12 and 19 months of age. The first cross ewes were the progeny of Merino ewes mated to 30 individual sires from several maternal sire breeds, including Border Leicester, East Friesian, Finnsheep and Coopworth. Milk production of the ewes was measured at ~3, 4 and 12 weeks of lactation using a 4-h milk test. The effect of ewe milk production on lamb growth rate in Period 1 included a significant interaction with lamb birth and rearing type (P &lt; 0.001). These regressions were 52 ± 18 g/day per kg/day for single born and reared, 24 ± 17 g/day per kg/day for multiple born and single reared and 18 ± 17 g/day per kg/day multiple born and reared lambs. The regression of ewe milk production in Period 2 on lamb growth rate in Period 2 was also significant (P &lt; 0.001), although milk production in Period 1 accounted for more variation in lamb growth. There were significant interactions of ewe weight gain (from mid pregnancy to lamb weaning) with season in Period 1 (P &lt; 0.01) and year in Period 2 (P &lt; 0.001). There was also a significant interaction (P &lt; 0.001) of year with ewe mid-pregnancy weight for lamb growth in Period 2. Lamb birthweight had a significant effect on lamb growth rate in Period 2 (regression coefficient 6.68 ± 2.57 g/day.kg, P &lt; 0.01).

Genetic evaluation of crossbred lamb production. 5. Age of puberty and lambing performance of yearling crossbred ewes

The age and liveweight at puberty were evaluated in 2155 crossbred ewe lambs at 2 sites over 3 years. A separate dataset examined the lambing performance of 1177 crossbred ewe lambs that were joined naturally at ~7 months of age at 2 sites over 3 years and also their lambing performances in the subsequent 2 years. The ewe lambs were the progeny of Merino dams and sires from several breeds including Border Leicester, East Friesian, Finnsheep, Coopworth, White Suffolk, Corriedale, and Booroola Leicester. Overall, 85% of the ewe lambs reached puberty (detected by teasers) in their first autumn at an average age of 248 days and liveweight of 42 kg. There was significant variation in age and weight at puberty (P &lt; 0.01) among the site and year cohorts of ewes. Sire breed was significant for weight (P &lt; 0.01) but not age at puberty. Of the crossbred ewe lambs joined at 7 months of age, 54% lambed with an average litter size of 1.31 and 49% of lambs were weaned from the ewes joined. There was a significant site effect for all reproduction traits (P &lt; 0.01), with the higher performance at one site associated with higher liveweight at joining. Maternal sire breed was significant for all reproduction traits (P &lt; 0.01) and there was considerable variation between sires within sire breeds. Ewes that reared lambs in their first year weaned 12% more lambs per year in their second and third years compared with ewes that failed to lamb or rear any lambs at 1 year of age. The results demonstrate that lamb weaning rates of 90% or more can be achieved from crossbred ewe lambs with optimal genetics and management. The opportunities for improving productivity by joining crossbred ewe lambs and the selection and management considerations required for successful joinings and lambings are reviewed and discussed.

Milk yield and milk composition from grazing primiparous non-dairy crossbred ewes

Milk production and milk composition were studied in 520 primiparous Merino crossbred ewes that were the progeny of 30 sires from several maternal crossing breeds including Border Leicester, Coopworth, Finnsheep and East Friesian. The ewes were born in 3 years (1997, 1998, and 1999), with 3 sires used in every year to provide genetic links. The crossbred ewe lambs were randomly assigned to autumn or spring joining groups and mated to Poll Dorset rams to lamb at 12 or 19 months of age. Ewes were milked on 3 days during their first lactation at approximately 3, 4, and 12 weeks after lambing. On each milking day, each ewe was initially injected with oxytocin, milked out by machine, and then hand-stripped. This procedure was repeated approximately 4 h later, with the milk weight and time recorded to extrapolate to daily milk yield, and composition of the milk was determined. Daily milk yield was analysed using REML mixed models procedures and 3 measures of milk production were predicted: peak milk yield at 21 days of lactation, total milk yield from 21 to 90 days of lactation, and length of lactation (days for daily yield to decline to 600 g/day). Milk composition traits (%fat, %protein, %lactose) and proportion of machine milk yield were analysed with similar models. Sire breed, number of lambs born and suckled, season, and ewe weight gain from mid-pregnancy until lamb weaning were all significant (P &lt; 0.01) for daily yield, which declined from 2.1 kg/day at 21 days to 0.7 kg/day at 90 days of lactation. The Finnsheep-cross ewes had lower peak milk yield (1.84 ± 0.08 v. 2.09–2.19 ± 0.1 kg/day) and lower total yield of lactation (21–90 days) than all the other breed-cross ewes (78 ± 3 v. 92–107 ± 5 kg). The East Friesian-cross ewes had significantly longer lactations (128.8 ± 10.9 days) than the Border Leicester (98.1 ± 4.4 days) and Coopworth (93.7 ± 4.2 days), with the Finnsheep-cross ewes the shortest (80.1 ± 3.1 days). The East Friesian-cross ewes had the greatest and the Finnsheep-cross ewes the least total yield of lactation (107 ± 5 and 78 ± 3 kg, respectively). There were significant differences in peak milk yield for ewes bearing and suckling single lambs, twin-born and single-raised lambs, and twin-born and raised lambs (1.86 ± 0.04, 2.03 ± 0.09, and 2.37 ± 0.07 kg/day, respectively). There was a significant decline in daily milk yield with increasing ewe weight gain from mid-pregnancy to lamb weaning (–18.1 ± 4.2 g/kg). All the components of milk composition changed from the peak of milk production at 3 weeks to the end of lactation. The East Friesian-cross ewes had significantly lower milk %fat (by approx. 1 percentage point) at both 21 days and 90 days of lactation than ewes by all other sire breeds. The 30 sire progeny mean deviations for daily milk yield ranged from –292 to +276 g/day, with considerable ranges between sires within the sire breeds. The implications for lamb production and breeding programs are discussed.

Mid-pregnancy shearing can increase birthweight and survival to weaning of multiple-born lambs under commercial conditions

In several field studies, mid-pregnancy shearing has increased lamb birthweight, which may be associated with an increase in lamb survival. However, animal numbers have been too low in these studies to accurately examine any effects on survival rates to weaning. This study was designed to investigate the effect of mid-pregnancy shearing on the birthweight of multiple-born lambs and their survival rates to weaning under commercial farming conditions at 2 different sites. At Riverside, 657 twin- and 47 triplet-bearing ewes were either shorn at mid-pregnancy (n = 347) or left unshorn (n = 357). Similarly, at Tuapaka, 532 twin-, and 60 triplet-bearing ewes were either shorn at mid-pregnancy (n = 291) or left unshorn (n = 301). Mid-pregnancy shearing significantly (P&lt;0.05) increased the birthweights of lambs at each site (by 0.44 and 0.13 kg at Riverside and Tuapaka, respectively). Mid-pregnancy shearing significantly (P&lt;0.05) increased lamb weaning weights (by 1.07 kg) and survival rates to weaning (by 5.5%) at Riverside, but not at Tuapaka. These findings show that mid-pregnancy shearing under commercial farming conditions can increase the birthweight of multiple-born lambs and, when the birthweight response is large enough to reduce the numbers of otherwise lightweight lambs, it is associated with an increase in survival rates to weaning.