Oestrous cycle dynamics in peri-pubertal and mature Javanese thin-tail sheep

Abstract

Duration of oestrus, time of ovulation and hormone profiles for progesterone and LH in prepubertal, pubertal and mature Javanese thin-tail sheep were studied at synchronized oestrus following progestagen-PMSG treatment and at the first natural oestrus after synchronization. The ewe lambs responded to progestagen-PMSG treatment by showing earlier onset of oestrus and an earlier and higher peak of LH concentration than mature ewes. For pre-pubertal, pubertal and mature ewes the mean LH peaks were 49.9, 43.9 and 37.9 ng/ml ( P>0.05) at mean intervals of 7.5, 8.4 and 16.5 h ( P < 0.05), respectively, after onset of oestrus. Duration of oestrus was 41.2 h in pubertal lambs and averaged 37.5 h in the other two groups ( P>0.05). Except in one mature ewe, ovulation occurred between 24 and 36 h after onset of oestrus and the majority ovulated at around the end of oestrus. The corpora lutea developed normally, as indicated by plasma-progesterone changes. The patterns of plasma-progesterone changes were similar in all three groups, though the concentrations were lower in the ewe lambs. At the first natural oestrus after synchronization, mature ewes showed longer ( P>0.05) oestrus (31.5 vs. 24.3 h), longer time interval from onset of oestrus to the LH peak (16.0 vs. 12.0 h) and from the LH peak to ovulation (21.0 vs. 19.6 h) than peri-pubertal lambs. Six of eight pre-pubertal lambs did not ovulate at their first natural oestrus, resulting in a conception rate of 11% for that group, while in pubertal lambs and mature ewes conception rates were 70% and 100%, respectively.