Lamb Weaning Weight Research Articles

Oestrous synchronisation and twinning rate of Syrian Awassi ewes treated with progestagen and PMSG during the breeding season

An experiment was conducted on Awassi ewes, during the breeding season, to evaluate the effectiveness of intravaginal sponges for oestrous synchronisation and the effect of pregnant mare serum gonadotropin (PMSG) on twinning rate. Thirty intact ewes with an average live weight of 3.1 ± 9.1 kg were divided into 3 equal groups. Sponges containing 60 mg of medroxy‐progesterone acetate (MAP) were inserted for 13 days in ewes in groups Tl and T2. Ewes in the latter group (T2) were injected intramuscularly, at the time of sponge withdrawal, with 500 i.u. of PMSG. The third group (C), received no treatment and served as a control. The mean interval to onset of oestrus was 2.0 days (range: 1.2–3.0 days) and 2.1 days (range: 1.0–3.9 days) after sponge withdrawal for ewes in groups Tl and T2, respectively (P > 0.05). In the control group (C), time of onset of oestrus was more variable (mean: 4.2 days, range: 1–14 days). Differences between the treated and the control animals in the time of onset of oestrus were significant (P < 0.05). The mean concentration of progesterone at sponge withdrawal was 0.16 and 0.08 and at mating was 0.11 and 0.10 nmol 1‐1 for groups T1 and T2, respectively. The treatments had no effect on duration of pregnancy, lamb birth weight, or lamb weaning weight. Using PMSG at sponge withdrawal increased twinning rate from 20% in groups T1 and C to 50% in group T2. It is concluded that intravaginal sponges (MAP) can be used for oestrous synchronisation in local Awassi ewes during the breeding season and that treatment with PMSG at the end of MAP treatment increases twinning rate.

Characteristics of the American Polypay: A review

SummaryThe Polypay sheep breed was developed at the U.S. Sheep Experiment Station with a reproductive capacity markedly superior to that of domestic US western range breeds. The Polypay is a four breed composite of Targhee, Rambouillet, Dorset and Finnish Landrace breeds. It is a medium-sized wool sheep (average mature ewe weight of 72 kg) with a smooth body free of excessive skin wrinkles on the neck and body and a poll head. Comparative studies with other US domestic breeds have shown the Polypay to have earlier sexual maturity higher fertility and prolificacy rates. Mature ewes give birth to an average of 2.4 lambs and wean an average total litter weight of 63.8 kg per ewe at 120 days post partum. Lamb survival rates to 21 and 120 days are greater than those of other breeds compared. Average individual lamb weaning weight at 120 days (36.1 kg) exceeded that for Rambouillet and Targhee lambs (34.5 and 33.8 kg, respectively). Polypay carcasses are similar to those of Rambouillet and Targhee for dressing percentage, body wall thickness, kidney and pelvic fat, and ribeye area. Measures of carcass fat are less in the Polypay when compared to the Rambouillet and Targhee while qualitative leg scores for the Polypay were more favorable. Productive longevity under western range herded conditions does not differ among Polypay, Rambouillet, Targhee and Columbia sheep. In a farm flock production system, the average number of productive years for Polypay ewes exceeded that of most crossbred types. Wool characteristics are defined as a coarse to medium grade wool with a fiber diameter ranging from 24 to 33 μm. Fiber staple length ranges from 7.6 to 12.7 cm with a common mean of approximately 10 cm. Raw fleece weights are considered light and range from 2.7 to 4.5 kg. Yield of clean wool is approximately 57 percent. Economic evaluations favored the Polypay in all production systems considered with 15 to 36 percent increase in sales or profits compared to other US domestic breeds. When considering the Polypay breed for importation, some prudence should be exercised because it may not be suitable to all environments and production systems in the world, especially where nutritional and management resources are not sufficient to support lactating ewes rearing twins.

Environmental and genetic aspects of survival and early liveweight in Western Australian Merino sheep

(Co)variance estimates for birth weight, pre-weaning lamb survival and weaning weight were obtained for Merino lambs derived from 16 bloodlines. Between bloodline variance ratios (± s.e.) amounted to 0.10 ± 0.04 for lamb birth weight, 0.053 ± 0.036 for lamb survival (logit scale) and 0.18 ± 0.07 for lamb weaning weight. Direct additive genetic variances for weaning weight - expressed as a ratio of the total phenotypic variance within bloodlines (h2, direct heritability) - were estimated at 0.18 ± 0.02 for birth weight, 0.094 ± 0.020 (logit scale) for pre-weaning survival and 0.30 ± 0.02 for weaning weight. Corresponding maternal genetic variance ratios (m2) were estimated at 0.15 ± 0.02 for birth weight and 0.08 ± 0.02 for weaning weight. It was not significant in the case of lamb survival. Maternal permanent environmental variance ratios (c2) amounted to 0.08 ± 0.02 for birth weight, 0.044 ± 0.018 for lamb survival (logit scale) and 0.07 ± 0.02 for weaning weight. These results were discussed with reference to sheep production. (South African Journal of Animal Science, 2001, 31(2): 123-130)

Pregnancy Dagnosis in Sheep: Review of the Most Practical Methods

Karen A. , P. Kovacs, J .F. Beckers , O. Szenci : Pregnancy Diagnosis in Sheep: Review of the Most Practical Methods. Acta Vet. Brno 2001, 70: 115-126. Various practical methods have been used for pregnancy diagnosis in sheep. Both pregnancy and fetal numbers are accurately diagnosed by using radiography after day 70 of gestation. Rectal abdominal technique detects pregnancy with an accuracy of 66 to 100% from d 49 to 109 of gestation, however, it has a low (17 to 57%) accuracy for determining multiple fetuses. Progesterone assays have a high sensitivity (88% to 100%) and a low specificity (60% to 72%) at d 16 to 18. Estrone sulphate assay accurately detects pregnant ewe at d 30 to 35. Ovine pregnancy specific protein B (PSPB) assay accurately (100%) detects pregnancy from d 26 after breeding onwards. The accuracy of progesterone, estrone sulphate and oPSPB assays for determining fetal numbers is relatively low. A-mode and Doppler ultrasonic techniques accurately detect pregnancy during the second half of gestation. Fetal numbers cannot be determined by A-mode ultrasound, while the Doppler technique needs experience to achieve high accuracy. Transrectal B-mode, real time ultrasonography identifies the embryonic vesicles as early as d 12.8 after mating, but the sensitivity of the technique for pregnancy is very low (12%) earlier than 25 d after mating. Transabdominal B-mode ultrasonography achieved high accuracy for pregnancy diagnosis (94% to 100%) and the determination of fetal numbers (92% to 99%) on d 29 to 106 of gestation. Realtime, B-mode ultrasonography appears to be the most practical and accurate method for diagnosing pregnancy and determining fetal numbers in sheep. Pregnancy diagnosis, ewe, radiography, rectal-abdominal palpation, hormonal assays, pregnancy proteins, ultrasonography Early detection of pregnancy is of considerable economic value to sheep industry. Nonpregnant ewes could be sold, reducing feed expenses, while non-pregnant lambs could be marketed at higher price than they would bring as mature ewes (Gearhart et al. 1988). Separation of the sheep herd into pregnant and non-pregnant ewes might reduce reproductive and production losses in form of abortions, stillbirths and production of weak lambs (Wani et al. 1998). Predictions of the number of fetuses would allow appropriate nutritional management of the ewes in late gestation that will prevent pregnancy toxemia (Ford 1983), minimize prelambing feeding costs, optimize birth weight, weaning weight and survivability of lambs and reduce the incidence of dystocia (Gearhart et al. 1988). In addition, the accurate information on the stage of gestation would be useful to dry off lactating females at adequate period and to monitor the females near term (Doize et al. 1997). Methods of pregnancy diagnosis Various methods have been used to diagnose pregnancy in sheep. These methods can be classified as less practical such as the management method (non-return to estrus), abdominal ACTA VET. BRNO 2001, 70: 115–126 Address for correspondence: Aly Karen Department of Obstetrics and Reproduction, Faculty of Veterinary Science, Szent Istvan University, Istvan ut., H-1400 Budapest, P. O. Box 2, Hungary Phone: +361-4784206 Fax : +361-478-4207 e-mail: akaren@univet.hu

Tactical versus continuous stocking in perennial ryegrass-subterranean clover pastures grazed by sheep in south-western Victoria. 3. Herbage nutritive characteristics and animal production

A 4-year grazing experiment was carried out in south-western Victoria to compare the effect of tactical stocking with continuous stocking on the persistence of perennial ryegrass (Lolium perenne L.) and the productivity of sheep used for prime lamb production. Tactical stocking consisted of variable length summer, autumn and winter rotations and continuous stocking in spring. The 2 grazing strategies were compared on 2 contrasting pastures: an upgraded pasture, sown with newer cultivars of perennial ryegrass and subterranean clover (Trifolium subterraneum L.) with 26 kg phosphorus/ha.year, and a naturalised perennial ryegrass pasture receiving 6 kg phosphorus/ha.year. Paddocks were grazed by Border Leicester x Merino ewes, which were mated to a terminal sire to lamb in September. In this final paper of the series, the effects of the grazing systems and pasture treatments on animal production and herbage quality are presented. The liveweights of the ewes were similar across all treatments during autumn and winter, but the tactically stocked ewes were 3–6 kg lighter than continuously stocked ewes during spring and summer. The lower liveweight was attributed to the lower (P&lt;0.001) herbage quality on the tactically stocked pastures in spring (P&lt;0.001). Both digestibility and crude protein concentration were about 4 percentage units lower with tactical stocking in spring. This lower quality was associated with the higher herbage mass (by 500–900 kg dry matter/ha) on the tactically stocked pastures, which presumably had a higher stem:leaf ratio and showed reproductive growth earlier than the continuously stocked pastures. Although there were differences in ewe liveweight, this did not affect individual lamb weaning weight or ewe fleece weight. There were significant increases in production per hectare from tactically stocked or upgraded pasture treatments due to the higher stocking rates that could be carried, 9 and 51%, respectively. In 1998, 544 kilograms of lamb per hectare was weaned from continuously stocked paddocks and 607 kg/ha from tactically stocked paddocks (P&lt;0.05), and 449 and 702 kg/ha from the typical and upgraded pastures, respectively. This study reinforces the view that soil fertility and pasture improvement have a much greater impact on animal productivity than changes to grazing method with little effect on per head productivity. The negative impact of rotational stocking on herbage quality reinforces the need to use these systems strategically when benefits from increased herbage mass are expected to increase animal production or overcome sustainability or pasture persistence problems.

Investigation of direct and maternal genetic effects on birth and weaning weight of Chios lambs

Direct additive and maternal genetic effects on birth and weaning weight of Chios lambs were investigated. The data originated from the Agricultural Research Station of Chalkidiki and comprised 7318 lambs, raised over the period from 1977 to 1992. Variance components were estimated using restricted maximum likelihood, fitting six different animal models, by including or excluding maternal effects. The direct heritability ( h 2 d ) for birth weight decreased from 0.38 to 0.13 when maternal genetic effects were included in the model, while h 2 d for weaning weight decreased from 0.29 to 0.15. The maternal heritability ( m 2) for birth weight was 0.33 when only maternal genetic effects were included in the model and ranged from 0.13 to 0.19 when the permanent environment of the dam ( c 2) was added. The respective values of m 2 for weaning weight ranged from 0.14 to 0.16 and 0.05 to 0.07. The permanent environmental effect of the dam was significant for both traits. Negative genetic covariance between direct and maternal genetic effects ( σ am ) was observed, which was significant only for birth weight.

Increasing lamb output by crossing commercial Merino ewes with South African Meat Merino rams

Commercial Merino ewes were randomly allocated to 1 of 2 groups, which were joined either to commercial Merino or South African Meat Merino rams during October 1996 and 1997. Merino rams were involved in 161 joinings, and South African Meat Merino rams in 157 joinings. The proportions of ewes that lambed were independent of the breed of the sire when expressed relative to the number of ewes joined (0.809 and 0.801 in ewes joined to South African Meat Merino and Merino rams, respectively). The proportion of multiple lambs was similarly not affected by the breed of the service sire. Lambs sired by South African Meat Merino rams were on average ( s.e.) heavier (4.17 0.07 v. 3.86 0.07 kg; P&lt;0.01) at birth. They also tended to have a better (0.69 v. 0.59; P&lt;0.10) survival to weaning, and were heavier (26.9 0.6 v. 22.8 0.6 kg; P&lt;0.01) at weaning than purebred Merino contemporaries. The combined effect of the tendency towards an improved survival rate as well as the increased lamb weaning weight resulted in a 36% increase (P&lt;0.01) in lamb output in Merino ewes joined to South African Meat Merino ewes compared with ewes joined to Merino rams. Higher (P&lt;0.01) proportions of ram lambs sired by South African Meat Merino rams reached slaughter weight (about 40 kg) before the onset of the dry Mediterranean summer than purebred Merinos. Two-tooth ewes sired by South African Meat Merino rams were heavier (P&lt;0.01) at 2-tooth age (53.0 0.6 v. 52.0 0.6 kg) than purebred Merinos. The 2-tooth greasy fleece weight of South African Meat Merino sired 2-tooth ewes were lower (3.85 0.08 v. 4.66 0.09 kg; P&lt;0.01), with a lower (66.8 0.6 v. 70.5 0.7 %; P&lt;0.01) clean yield than that of purebred Merinos. This resulted in a marked difference in clean fleece weight between the 2 types (2.56 0.06 v. 3.28 0.06 kg, respectively). Wool produced by South African Meat Merino sired 2-tooth ewes was generally broader (21.8 0.3 v. 20.3 0.3 m; P&lt;0.01) and shorter (87.3 1.3 v. 96.4 1.4 mm; P&lt;0.01) than that of their purebred Merino contemporaries. The coefficient of variation of fibre diameter as well as staple strength was independent of the breed of the sire. Liveweight of adult ewes and wool traits were independent of the breed of the service sire.

Lamb and milk production traits of Serrai sheep in Greece

This study is based on data from 1238 lambings, 1516 lambs and 979 lactation records from Serrai ewes. Litter size averaged 1.25 lambs at birth, 1.23 lambs born alive and 1.17 lambs at weaning. Lambs weighed 4.3 kg at birth and 13.5 kg at weaning (42 days). Milk production averaged 70.7 kg in a lactation length of 157 days. Month of lambing influenced litter size, lamb birth and weaning weight, milk yield and lactation length ( P < 0.05). Lactation number influenced litter size, lamb weaning weight, milk yield and lactation length ( P < 0.05). There was a significant effect of litter size on lamb weight at birth and weaning and on milk production. The ewe weight at lambing had a significant effect on weights of lambs at birth and weaning and on milk production.

The long-term influence of superphosphate and stocking rate on the production of spring-lambing Merino sheep in the high rainfall zone of southern Australia

The productivity of spring-lambing fine wool Merino sheep grazing pastures sown in 1977 to perennial ryegrass and subterranean clover was assessed from 1989 to 1998. The pastures were fertilised each autumn with single superphosphate at 6 levels, and were stocked at a low, medium, or high stocking rate (SR) at each level of fertiliser. The average phosphorus (P) applied annually since sowing (P ) ranged from 1.6 to 32.9 kg/ha. The SRs used varied with fertiliser level in that they were higher where more fertiliser had been applied, so that the highest SR at each level of fertiliser ensured that the pastures were well utilised. Each ewe raised 1 lamb, which was removed at weaning. The influence of fertiliser on the productivity of the sheep at 4 classes (1–4) of SR (mean SR = 7.1, 10.1, 12.6, and 18.2 ewes/ha for classes 1–4, respectively) was described by: y = A−BCP, where y represents production per sheep (kg), and A, B, and C are constants. For greasy fleece weight, estimates of B and C were 1.59 and 0.84; and for SR classes 1–4, the estimates of A were 5.06, 4.89, 4.78, and 4.46, respectively. For weaning weight of lambs, estimates of B and C were 8.4 and 0.82, and estimates of A were 23.5, 22.7, 21.5, and 20.9 for SR classes 1–4. The mean fibre diameter (µm) of the wool was described by: D = 14.18+1.48 GW, where GW is the mean greasy wool produced annually per sheep (kg) averaged over all sheep and years for each of the 18 treatments. The price (cents/kg) of wool with a fibre diameter D (P D) was given by: P D = 12197+4.94P2 + 688D−0.1945P20D − 5810√D, where 20 µm wool is P20 cents/kg. Supplements were fed if the body condition of ewes fell to a predetermined level. The supplement fed per ewe each year (S), expressed as metabolisable energy (in MJ) was described by: S = −602 − 44.1S R + 178.5P + 8.71S R P +539 √SR− 338.5√P−70.8P√SR, where S R and P represent the mean stocking rate (ewes/ha) and mean P applied annually. When a current set of costs and prices was applied to these equations, the maximum gross margin for a SR of 7.1 ewes/ha was $AU119/ha with 8.6 kg P/ha applied annually, and $AU262/ha for SR of 18.2 ewes/ha with 17.6 kg P/ha applied annually. If income derived from sheep is maintained constant, intensifying the sheep enterprise from the low to the high SR system would involve increasing sheep numbers by about 17%, but would release about 55% of the farm’s area for another purpose.

Continuous urea-molasses supplementation for Sumatra thin tail ewes grazing in rubber plantation : Reproductive performances.

The reproductive responses of local Sumatra ewes on the continuous urea-molasses supplementation was studied in 116 ewes for 21 months. The animals were divided into two groups and randomly allocated to urea-molasses supplement and grazing in rubber plantation or grazing in rubber plantation only (control). Both groups were allowed to graze for 8 hours a day. The urea-molasses mixture contained 3% urea (kg/kg) and were fed to the supplemented ewes ad libitum . The number of lambs born from supplemented ewes were greater than control (166 vs 114 heads). This was associated with the higher (P 0.10) between the treatments (1.79 vs 1.61 kg), but weaning weight of lambs born to the supplemented ewes were greater (P<0.05) than the unsupplemented ewes (8.90 vs 7.55 kg). The ewe’s weight after parturition and the weight of lambs weaned per year were also greater (P<0.05) in the supplemented group compared to the control (22.7 vs 20.6 kg and 20.2 vs 15.1 kg, respectively). It was concluded that urea-molasses mixture was a good feed supplement for ewes grazing in rubber plantation. The urea-molasses supplementation clearly had positive effects on ewe and lamb productivity. Key words : Urea, molasses, ewes, reproductive performances

The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK. 4. The effect of seasonal pattern of nitrogen fertilizer application and annual stocking rate

Greyface (Border Leicester × Scottish Blackface) ewes, mated in October, were housed in winter and turned out after lambing in late March to one of four treatments replicated three times on perennial ryegrass (Lolium perenne)‐dominated pastures. On three of the treatments the stocking rate was 12·5 ewes plus lambs ha−1 annum−1 (SR12·5), whereas on the fourth it was 15·0 ewes plus lambs ha−1 annum−1 (SR15·0). There were two levels of applied fertilizer nitrogen (N), 152 kg N ha−1 annum−1 (N152) and 205 kg N ha−1 annum−1 (N205). Three patterns of nitrogen application were used: predominantly in spring (E), predominantly in autumn (L), and mainly in spring and autumn (E + L). Grazed sward surface height was controlled within the range 3·5–5·5 cm during spring and summer, and supplementary feed was offered when sward height was below 3·5 cm.The effects on animal performance, yield of silage and requirement for supplementary feed were measured over 3 years (1986–88). Management of the sward height within the specified limits resulted in similar levels of individual animal performance for all treatments, but treatment SR15·0N205E + L produced a significantly (P &lt; 0·05) greater output of lamb per hectare. There was no evidence to suggest that, by increasing the amount of N fertilizer applied in the autumn, ewe reproductive performance was increased. Neither the treatment with the lower level of N applied in the spring (SR12·5N152L) nor the high stocking rate treatment (SR15·0N205E + L) was self‐sufficient in winter feed (silage) production. SR15·0N205E + L also required more supplementary feed in both the lactation (38·1 kg ewe−1) and the mating (9·1 kg ewe−1) periods. SR12·5N152L required the second greatest amount of supplementary feed during lactation (36·1 kg ewe−1), whereas SR12·5N205E + L required the least supplementary feed over both periods (27·8 kg and 4·8 kg ewe−1). Taking all treatments together, there were significant (P &lt; 0·05) differences between years in lamb weaning weight (kg), lamb output (kg ha−1), yield of silage (kg ewe−1) and supplementary feed required (kg ewe−1), arising mainly from a lower level of herbage production in one year. Treatment SR12·5N152E generated the highest gross margin per hectare.

Comparison of Lohi and crossbred ewes: productive and reproductive traits

Data from 6305 lambings of Lohi, 7/8 Lohi: 1/8 Awassi (LA) and 7/8 Lohi: 1/8 Kachhi (LK) ewes from 1981 through 1993 were used to analyse growth and reproductive traits and wool production. Mean litter size at birth ranged from 1.37 for Lohi ewes to 1.41 for LA ewes and corresponding values at weaning were 1.32 and 1.30, respectively. Litter size varied among ewe age and season of lambing ( P<0.01). Litter size was consistently lowest for one-year-old, with a substantial increase at two, three and four years of ewe age and marginal increase thereafter. Ewes lambing in spring weaned 0.10 more lambs than ewes lambing in autumn ( P<0.01). Lamb birth weights were affected by ewe genotype ( P<0.01) and increased with ewe age. Mean lamb weaning weight (120 d) of 5587 lambs was 22.1 kg, which was affected by genotype, sire, year of birth, sex, litter size and weaning age ( P<0.01). Lambs from LK ewes were heaviest at weaning (23.0 kg) followed by lambs from LA ewes (22.9 kg) and Lohi ewes (20.5 kg). Lambs from crossbred ewes were 5% heavier at birth and 12% heavier at weaning than pure Lohi lambs. Twin-born lambs were 18% lighter at birth and 17% at weaning than single-born lambs. Male lambs were 7% heavier at birth and 14% heavier at weaning than female lambs. Lohi ewes produced 3% more wool than crossbred ewes. Crossbred ewes were superior to pure Lohi ewes by 2% in litter size at birth, 5% for lamb birth weight and 12% for lamb weaning weight. Heterozygosity among the crossbred ewes has resulted in improved productivity over purebred Lohi ewes.

Responses to various selection protocols for lamb production in Rambouillet, Targhee, Columbia, and Polypay sheep.

To investigate the effectiveness of four selection protocols for improving reproduction in sheep, we evaluated nine selection lines and two random-bred control lines for lamb and wool production. Results were based on 25,026 dam and 30,628 lamb records from Rambouillet (R), Targhee (T), Columbia (C), and Polypay (P) sheep collected from 1976 through 1988. Phenotypic trends over years were positive (P < .01) for most reproductive traits, body weight, wool grade (coarser grades), and lamb weaning weight in nearly all selected lines. Small positive trends for both random-bred control lines indicated there were improvements in management and(or) environment during the period. Small but significant phenotypic declines in fleece weights occurred in most lines, including controls. Substantial genetic gains (P < .01) in litter weight weaned (120 d), net reproductive rate (lambs weaned divided by ewes mated), prolificacy, body weight, and weaning weight were made in nearly all selected lines. There were also small but significant improvements in milk score in most lines. There were significant genetic declines and improvements in fleece weights; however, the average genetic change in fleece weight for lines selected for litter weight weaned was negligible. Genetic improvement in litter weight weaned was attributed approximately 37% to prolificacy, 27% to percentage of lambs weaned, 17% to lamb weaning weight, 12% to fertility, and 7% to ewe viability from breeding to lambing. On average, selection based on independent culling levels (litter weight weaned plus yearling body weight), yearling body weight, or early puberty was only 85, 67, or 59%, respectively, as effective as that based solely on litter weight weaned for improving litter weight weaned. The net value of the average (over all breeds) annual increase in production per ewe resulting from selection for litter weight weaned accumulated over 12 yr to an estimated $11.40 and $21.51 annually for genetic and phenotypic increases, respectively.

A long-term study of superphosphate and stocking rate on sheep production and plant and soil characteristics in central west New South Wales

Summary. The effect of 4 rates of superphosphate application (250 kg/ha. year, 125 kg/ha. year, 125 kg/ha every 2 years or 125 kg/ha every 4 years) and a low and high stocking rate (3.6 and 5.4 ewes/ha, 1980–86; and 4.0 and 7.0 ewes/ha, 1986–89) on sheep liveweight, fleece weight, lamb weaning weight, pasture production and botanical composition, soil pH, soil phosphorus, manganese and aluminium concentrations were measured on a Phalaris aquatica–subterranean clover pasture at Stuart Town, New South Wales. Only when 250 kg/ha of superphosphate had been applied annually was there a higher level of soil phosphorus than with the other 3 systems. None of the treatments affected soil pH, soil manganese or aluminium. There were large year effects and individual plot effects on pasture and sheep production but neither the superphosphate rates nor stocking rate significantly affected pasture or animal production. It was concluded that over a 9-year period the application of 125 kg/ha in alternate years can maintain adequate soil phosphorus levels, and satisfactory pasture and animal production on the central tablelands of New South Wales.

Lamb survival in relation to lambing and neonatal behaviour in medium wool Merino lines divergently selected for multiple rearing ability

Summary. Two lines of Merino sheep were divergently selected from the same base population since 1986 on maternal ranking values for multiple rearing ability. In the high (H) line, ewe and ram progeny were preferably descended from ewes that reared &gt;1 lamb per joining. In the low (L) line, replacements were the progeny of ewes that reared &lt;1 lamb per joining. Data on lamb mortality, lambing and neonatal behaviour as well as lamb production were obtained from these lines over 5 years (1993–97). Lamb survival was improved (P&lt;0.01) in the H line, mainly as a result of the improved survival of multiples. It was evident that the survival of lambs was not compromised by selection for ewe multiple rearing ability, despite the fact that higher mortality levels are expected with an increase in multiple birth rate. No line difference was found for the time lapse from birth to first standing for &gt;10 s, but H line lambs were quicker (P&lt;0.01) to progress from standing to suckling than L line contemporaries (28 v. 38 min respectively). This line difference remained after adjustment for better co-operation of H line ewes with the first suckling attempts of their progeny. Ewes in the H line tended (P = 0.18) to remain longer on or near their birth sites than L line contemporaries (403 v. 362 min respectively). They also tended to be less (P = 0.07) likely to desert their lambs than L line ewes (12/424 = 0.028 v. 14/230 = 0.061 respectively). After least-squares adjustment for their heavier (P&lt;0.01) litter weight, H line ewes experienced shorter (P&lt;0.05) births than their L line contemporaries (46 v. 57 min respectively). Fewer (P&lt;0.05) H line lambs died during or shortly after parturition (respective proportions of 22/890 = 0.025 and 25/441 = 0.057), while maiden H line ewes were less (P&lt;0.05) likely to be assisted at lambing than L line contemporaries (4/107 = 0.037 v. 8/61 = 0.131 respectively). With regard to overall lamb production, it was found that the number of lambs weaned per ewe present at lambing in the H line was improved (P&lt;0.05) in all years relative to that observed in the L line, the differences ranging from 25% in 1993 to 47% in 1997. Lamb weaning weight was correspondingly improved (P&lt;0.05) in H line lambs, the differences ranging from 8% in 1994 to 22% in 1996. Fairly high levels of production could thus be attained with predominantly pasture-fed ewes selected for multiple rearing ability.

Pasture management to minimise the detrimental effects of pre‐lamb shearing

The purpose of this study was to examine whether the performance of pre‐lamb shorn sheep is influenced by pasture allowance in the immediate post‐shearing period and whether the relationship between performance and pasture allowance differs according to whether the ewes are shorn by standard comb or cover comb. The trial was replicated across two years to allow for climatic variations between years. Fifty‐four ewes were used in each year in a 3 × 3 × 2 factorial design with three shearing treatments (standard comb, cover comb, and unshorn), three sward surface height (SSH) treatments (nominal 3, 5, and 7 cm), and two pregnancy status treatments (single and twin). Rectal temperatures of standard comb or cover comb ewes were significantly lower (P < 0.05) than those of unshorn ewes on day 2 following shearing (S2), and on S4, S8, and S20. Pasture allowance, however, did not affect rectal temperatures of shorn ewes. There was an interaction (P < 0.05) between shearing treatment and SSH. Thus, liveweight gains during the period from pregnancy day 115 (P115) to P135 were 275, 613, and 4518 g; 1557, 2314, and 3997 g; and 3623, 2894, and 3997 g for standard comb, cover comb, and unshorn (control) ewes set‐stocked on 3, 5, and 7 cm SSH, respectively. There was no interaction between shearing treatment and SSH for lamb birth weight, but the birth weights of lambs born to standard comb ewes (4.9 ± 0.1 kg) were significantly greater (P < 0.05) than those of lambs born to unshorn ewes (4.3 ±0.1 kg). There were no effects of shearing treatment or SSH on lamb weaning weight, ewe wool growth rate or mean fibre diameter. Likewise, there were no effects of shearing treatment or SSH on ewe organic matter intake (OMI), except on the second day following shearing when the OMIs of ewes set‐stocked on 3 cm (941 ± 147 g) were significantly (P < 0.05) lower than those of ewes grazing 5 cm (1628 ±101 g) or 7 cm (1349 ± 135 g) SSH pasture. The results suggest that hypothermia, as determined by rectal temperatures and induced by pre‐lamb shearing, cannot be avoided by pasture management, provided SSH exceeds 3 cm. This reflects the fact that, in the period immediately after shearing, ewes do not increase feed intake when provided with increased pasture allowances.

Lamb growth and milk production of hair and wool sheep in a semi-arid tropical environment

St. Croix White hair ( n = 11), Barbados Blackbelly hair ( n = 10) and Florida Native wool ( n = 9) ewes were used to evaluate milk production and lamb growth under semi-arid tropical conditions. Milk production was measured on day 3 after lambing and at weekly intervals beginning on day 7 through weaning on day 63. Milk production decreased over time in St. Croix White and Barbados Blackbelly ewes more rapidly than in Florida Native ewes ( P < 0.01). Total milk yield was not different ( P > 0.1) among Barbados Blackbelly, Florida Native and St. Croix White ewes, or between ewes raising single or twin lambs. Udder volume was largest ( P < 0.08) in St. Croix White ewes, smallest in Florida Native and intermediate in Barbados Blackbelly ewes. All ewes had similar patterns of weight change during the study, but Barbados Blackbelly ewes weighed less than either St. Croix White or Florida Native ewes ( P < 0.05). There was no difference ( P > 0.1) in lamb weaning weight or average daily gain among the three breeds. The results show that Barbados Blackbelly, Florida Native and St. Croix White breeds of sheep produce similar amounts of milk and wean similar size lambs under tropical conditions, even though there are breed differences in body and udder size.

Genetic resistance of different genotypes of sheep to natural infections with gastro-intestinal nematodes

AbstractDuring a 3-year period, from April 1991 to December 1993, in a flock with four lambing periods annually, faecal samples from lambs at weaning at the age of 3 months (no. = 1756), were examined for gastro-intestinal nematode eggs by the McMaster method. Faecal samples were also examined at the age of 9 (no. = 170), 12 (no. = 157), 15 (no. = 253) and 18 (no. = 85) months from the females only. From June to December 1993 packed cell volume (PCV) was also examined from lambs at weaning. Seven genotypes were used in this study.The faecal egg counts were affected by genotype, birth season, type of birth and rearing, sex and age. First generation cross of Sumatra × Barbados Blackbelly had lowest eggs per g of faeces (EPG) followed by Sumatra, St Croix, Sumatra × St Croix Fl and F2 and Sumatra × Java Fat tail. Lambs born in February-March when rainfall was low had lower EPG (V &lt; 0·05) than those born in May-June or August-September. The EPG of lambs born and reared singly were significantly lower (P &lt; 0·001) than those born twin, triplet or quadruplet. Female lambs had lower EPG than male lambs (P &lt; 0·001). The EPG of lambs at 3 months were higher than at 9, 12, 15 or 18 months (P &lt; 0·001).PCV was affected by genotype, sex, type of birth and rearing and season of birth. There was a positive correlation between PCV and weaning weight of lambs and a negative correlation between EPG and weaning weight. These results show that the crosses of St Croix and Barbados Blackbelly with local Sumatra sheep are at least as resistant or more resistant to gastro-intestinal nematodes than pure Sumatra breed and therefore these breeds can be used in cross breeding programmes to improve the body size of local Sumatra sheep.

Supplementation of high fecundity Border Leicester x Merino ewes with a high protein feed: its effect on lamb survival

Two hundred and fifty Border Leicester x Merino ewes (40% heterozygous for the Booroola Fec B gene) were used in an experiment, replicated over 2 years, to examine the effects of cottonseed meal-based supplementation on lamb survival, birth, marking and weaning weight, as well as, liveweight and fleece characteristics of ewes. From 50 to 100 days of pregnancy, half of the ewes were supplemented with 80 g/head.day. The supplemented group was then split according to litter size and, until 30 days after lambing, were offered pellets at 80, 160 and 220 g/head .day, respectively, for ewes bearing single, twin and triplet (or more) lambs. Over the 2 years, ewes averaged 2.11 lambs per parturition and supplementation significantly increased lamb survival to weaning (73 v. 58%) with no interaction with litter size. Although supplementation had a positive effect on birth weight of all but twins, the effects of supplementation on survival were independent of birth weight effects. Significant effects of year, sire breed and litter size on lamb survival and birth weight were also noted. No effects of supplementation were apparent on lamb growth while ewe age, sire breed, sex and rearing rank all significantly influenced growth rates. Ewe weights, fleece weights and staple strength were significantly influenced by year, ewe age and litter size but not by supplementation. These findings indicate the benefits to lamb survival of providing a 'bypass' protein supplement to high fecundity flocks even when ewes are grazing good quality pastures.

Performance of hair breeds and prolific wool breeds of sheep in southern Illinois: lamb production of F1 adult ewes

Two- and three-year-old F1 crossbred ewes produced from Suffolk and Targhee dams and sires of the prolific wool breeds of Finnsheep, Combo-6, and Booroola Merino and the hair breeds of St. Croix and Barbados were pasture-mated to Dorset rams over a 4-yr period at the Dixon Springs Agricultural Center in Southern Illinois. Booroola Merino sires were homozygous for the FecB allele for high number of ovulations. The effects of age of ewe, sex of lamb (where appropriate), breed of dam, and breed of sire on condition score, breeding weight, ovulation rate, breeding to lambing interval, fertility, prolificacy, lamb survival, weaning weight, and ewe productivity were estimated. All traits were analyzed using mixed-model methodology. Crossbred ewes from Suffolk dams had a higher (P < .01) condition score, heavier (P < .01) breeding weight, higher (P < .01) ovulation rate, shorter (P < .01) breeding to lambing interval, greater (P < .01) prolificacy, heavier (P < .01) lambs at weaning, and greater (P < .05) ewe productivity than crossbred ewes from Targhee dams. Ewes from hair-breed sires had lighter (P < .01) breeding weight, lower (P < .05) ovulation rate, shorter (P < .05) breeding to lambing interval, higher (P < .05) fertility, higher (P < .05) lamb survival, lower (P < .10) lamb weaning weight, and higher (P < .05) ewe productivity than ewes sired by the prolific wool-breed rams. The breed of sire x breed of dam interaction was a significant source of variation for breeding weight, fertility, lamb survival, and ewe productivity.(ABSTRACT TRUNCATED AT 250 WORDS)