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This experiment, conducted in the humid lowland tropics of North Sumatra, Indonesia involved 132 young Sumatra (S); Virgin IslandSumatra (HC); and Barbados BlackbellySumatra (BC) ewes. The ewes were mated with rams of their same genotype and monitored until each ewe had weaned two crops of lambs. Data from 230 lambings and 350 lambs were included in the analysis. Mean ages at first and second lambing were 4653 and 6946 days, respectively. Mean interval between first and second lambings was 2315 days. Mean litter size averaged 1.520.04 at birth and 1.230.04 at weaning. There were no significant effects of genotype on age at lambing, lambing interval or litter size. Overall mean weights of lambs at birth and weaning were 1.810.02 and 9.50.1 kg. Genotype, type of birth and rearing, and sex of lamb affected lamb weights at birth and weaning. S lambs were the smallest (1.3 and 6.9 kg at birth and weaning). HC (1.8 and 9.6 kg) and BC (2.0 and 10.3 kg) were significantly heavier (p

A total of 196 young Sumatra (S) ewes and F1 crosses of S with Java Fat-tail (E1), Virgin Island (H1) and Barbados Blackbelly (B1) were mated with rams of their same breed type. The ewes were first exposed to the ram at 10 or 13 months of age, and reproductive performance was monitored until each ewe had reared two litters. Data from a total of 363 lambings and 563 lambs were included in the analysis. Mean ages at first and second lambings were 516 and 733 days. Litter size at birth ranged from 1 to 5 lambs with a mean of 1.55, and pre-weaning mortality (to 3 months) was 11.7%. There were no significant effects of breed type on age at lambing, lambing interval, litter size or mortality. The mean birth weights of lambs born to the S, E1, H1 and B1 ewes were 1.45, 1.62, 2.03 and 2.10 kg, respectively. Weaning weights averaged 8.5, 9.2, 11.7 and 12.1 kg for the four breed types. The differences among breed types were significant (P < 0.001) except for H1 and B1 which were similar. Litter size affected (P < 0.001) birth weights, weaning weights and pre-weaning mortality. A dam productivity index (DPI) for each ewe was calculated from the total weight of lamb weaned at the first two lambings divided by a measure of age. DPI was affected (P < 0.001) by breed type, and averaged 16.0, 18.1, 21.5 and 24.2 kg for the S, E1, H1 and B1 genotypes, respectively. Average weights of ewes at second lambing were 22.0, 24.4, 27.2 and 28.1 kg for the four genotypes, respectively. Thus, productivity expressed in terms of weight of lamb weaned per unit body weight of ewe was 0.73, 0.74, 0.79 and 0.86 for the S, E1, H1 and B1 genotypes, showing that the hair sheep crossbreds were more productive. DPI was slightly higher for ewes mated at 10 months of age than at 13 months, indicating no advantage in delaying first mating.

Sumatra ewes were mated to give Java Fat-tail crossbred (E1), Virgin Island crossbred (H1) and purebred Sumatra (S) lambs, or were inseminated to give Barbados Blackbelly crossbred (B1) lambs. A total of 882 lambs were born to 407 ewes in 568 lambings. Average litter size was 1.55 and lamb mortality to weaning at 3 months was 22.5%. Weights of lambs averaged 1.83 kg at birth and 8.7 kg at weaning. For female lambs only, weights averaged 14.4 kg at 6 months and 17.9 kg at 9 months of age. At weaning the average increases in weight of the crossbreds above S were E1 10–13%, H1 14–15% and B1 32%. At 3 months of age all breed groups had similar wool scores, but in older animals the ranking was B1 (least wool) < H1 < E1 < S (most wool).

Production performance of Javanese ewes (483 ewes with 1263 records) in West Java, Indonesia, was evaluated. The focus was on the effect of prolificacy and environmental sources of variation on lamb survival (S) as a ewe trait and on lambing and weaning outputs. Non-carriers (FecJ + FecJ + ), carriers (FecJ F FecJ + ) and homozygotes (FecJ F FecJ F ) for a gene affecting prolificacy, averaged 1.24, 1.95 and 2.59 lambs born, respectively. Prolificacy-year (PY) effects were significant, with FecJ F FecJ F animals being more sensitive to fluctuations. Repeatability for litter size was 0.51 and heritability 0.62. PY, gestation ewe weight gain (EGG) and parity significantly affected S. Singles, twins, triplets and quadruplets averaged 87, 69, 47, and 35% S, respectively, with fewer lambs surviving in these litter size categories in poor years. Repeatability of S was 0.19. Litter weaning weights (TWW) were influenced significantly by PY, parity and EGG. EGG contributed less than litter birth weight to the determination of S and TWW in all litters, although its contribution to TWW was proportionally higher than that to S. Repeatability of TWW was 0.20. Higher prolificacy led to a diminution of the ewe's body resources as indicated by EGG, therefore reducing the ewe's ability to support satisfactory birth weights of lambs and lactation, particularly under poor nutrition. With higher EGGs and survival rates under improved nutrition, a single copy of the FecJ F gene increased the productivity of ewes (TWW) by at least 18%; while under suboptimum nutrition, it had a negative effect. There is a need to investigate the nutritional management of animals having the FecJ F gene since the gene is widely distributed in most Indonesian sheep populations.

Repeatability within and between seasons for ovulation rate, and repeatability for litter size and embryo survival of Sardi (S), 3/4S 1/4D (Sardi backcross), F1, F2, 1/4S 3/4D (D'man backcross) and D'man (D) ewes were estimated by the intra-class correlation method. Within-season repeatability estimates for ovulation rate were 0.24, 0.56, 0.24, 0.29, 0.36 and 0.44 for Sardi, Sardi backcross, F1, F2, D'man backcross and D'man ewes, respectively. The pooled between-seasons repeatability estimates for ovulation rate, litter size and embryo survival were 0.26, 0.22 and 0.02, respectively. These repeatability estimates may be useful in a selection program for the improvement of these traits.

Data on four lamb crops in 2.5 years from an experimental flock of sheep established to compare prolific (D'Man) and nonprolific (Sardi) Moroccan breeds of sheep and their crosses are presented. Ovulation rate was recorded following matings of three of four seasons. Mean ovulation rates for ewes 30 months and over were 1.32 for Sardi and 3.18 for D'Man, with 99.7% 1's and 2's in Sardi ewes, and a range of one to seven, with 38% ≥ 4, in D'Man ewes. Prenatal survival was high in both breeds. Pregnant Sardi ewes with two corpora lutea (CL) had a survival rate of 89%, and D'Man ewes had survival rates of 90, 82, 69 and 58% for those with 2, 3, 4 and 5 to 7 CL, respectively. Repeatability of ovulation rate averaged 0.18 for Sardi and 0.29 for D'Man, with corresponding values for litter size of 0.18 and 0.27. Young F 1 ewes produced by mating D'Man rams to Sardi ewes were intermediate between the two parent breeds in ovulation rate, and had high prenatal survival.

Data on four lamb crops in 2.5 years from an experimental flock of sheep established to compare prolific (D'Man) and non-prolific (Sardi) Moroccan breeds of sheep and their crosses are presented. Conception rates, litter size, duration of postpartum anoestrus and age at puberty were recorded. Total productivity was consistently higher in the D'Man breed due to generally higher fertility and higher prolificacy. There were large seasonal variations in fertility of Sardi but not of D'Man ewes. Fertility of Sardi ewes was markedly affected by breed of sire used in mating, D'Man rams inducing a higher proportion of ewes to mate than Sardi rams. However, there was only a small effect of the breed of service ram on synchronization of oestrus. The postpartum anoestrus of D'Man ewes was always short (45 to 60 days) while in the Sardi it varied according to season of lambing, suggesting a winter-spring anoestrus. D'Man ewes had good fertility under one year of age and were close to mature litter size at second lambing at two years of age. Sardi ewes reached puberty at a much later age and did not achieve mature levels of reproductive performance before their third lambing. Ten to 11-month-old ewe lambs and 2-year-old F 1 ewes from Sardi dams were equal to D'Man ewes in fertility. The F 1 's reached puberty slightly later than D'Man but much earlier than Sardi and were intermediate between D'Man and Sardi purebreds in litter size.

Mortality and growth rates of D'Man (D), Sardi (S) and F 1 (D X S) lambs from four lamb crops from an accelerated lambing program are reported. Excluding the first season, when an outbreak of white muscle disease resulted in considerable death loss, mortality to 60 days was less than 10% for single and twin lambs from D'Man or Sardi dams, and less than 5% for single lambs from Sardi dams. There were triplets and higher multiples only in the D'Man breed. Mortality was 14% higher for triplets, and 38% higher for litters ≥ 4, than for twins. D'Man lambs weighed less than Sardi lambs at all ages, though less so than expected on the basis of the 50% higher mature weight of Sardi (48 kg) than of D'Man ewes (32 kg). Although F 1 lambs from Sardi dams were significantly lighter than Sardi lambs at birth, the difference was less apparent at 30 days and had disappeared by 60 days. Total weight of lamb weaned per ewe in the flock was highest for D'Man ewes in spite of their smaller size. Sardi ewes with F 1 (D X S) lambs had significantly higher productivity than Sardi ewes with S X S lambs. The results, along with those on reproduction, indicate that the D'Man breed has excellent potential for increasing total lamb production when crossed with less prolific breeds.