Comparison of Sumatra sheep and three hair sheep crossbreds II. Reproductive performance of F 1 ewes

Abstract

A total of 196 young Sumatra (S) ewes and F 1 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.