Studies on reproduction of Javanese thin-tail ewes

Abstract

Development of puberty (oestrus with ovulation) in two groups of 13 Javanese thin-tail (JTT) ewe lambs was studied from weaning at 13 weeks of age. The animals were fed ad lib. freshly chopped elephant grass plus either sufficient concentrate to grow at about 50 g per day (L) or ad lib. (H) concentrate from weaning to 5 weeks post-conception, and then studied through two pregnancies while on common feeding levels (Experiment 1). In Experiment 2, reproduction was studied in two groups of 13 JTT lambs which had been reared together and were given high or low nutrition from 5 weeks after their first conception until weaning of their second crop of lambs. The ewe lambs in Experiment 1 grew at 44 and 87 g per day (P < 0.01) for groups L and H respectively. Faster growth was associated with a younger age at first ovulation (190 v. 253 days), but differences in liveweight at first oestrus, first ovulation and puberty were marginal. Liveweight differences associated with differential feeding levels during rearing in Experiment 1 did not persist throughout the experimental period. Continuous high level feeding from early pregnancy (Experiment 2) resulted in a higher liveweight, and this was associated with higher ovulation rate (2.1 v. 1.6, P < 0.05) and an increase in the incidence of multiple births. However, this advantage in reproductive traits in the high feeding level group ewes was offset by higher wastage of ova (49 v. 20%) and higher pre-weaning lamb mortality (55 v. 33%). Average daily milk yield was non-significantly higher in the H group than in the L group in both lactations. In both experiments, improved feeding levels during rearing or thereafter reduced post-lambing re-breeding intervals. It was concluded that, while the JTT breed has unusually high, reproductive ability under low feeding regimes, most components of reproduction can be increased by strategic nutritional inputs.