Changes in plasma concentrations of LH, progesterone and oestradiol in relation to the occurrence of luteolysis, oestrus and time of ovulation in the Shiba goat (Capra hircus).

Luteolysis in Shiba goats was spontaneous (N = 5) or induced by prostaglandin F-2 alpha (N = 5). Blood sampling and the test for oestrous behaviour were carried out at 2-h intervals, and the time of follicular rupture (ovulation) was determined by culdoscopic observations performed every 2 h around the periovulatory period. In both groups plasma LH concentrations showed a temporary but significant increase during the abrupt fall in plasma progesterone concentrations at luteolysis. This LH rise may be responsible for the preovulatory development of antral follicles and the increase in oestradiol secretion from them. The total number of antral follicles (spontaneous luteolysis 3.6 +/- 0.6, induced luteolysis 4.2 +/- 0.7; mean +/- s.e.m.) and the number of ovulations (1.8 +/- 0.4, 2.4 +/- 0.2) did not differ significantly between the two groups. There was also no significant difference in the timing of oestrus, LH surge and ovulation following the two modes of luteolysis. The interval from luteolysis to the peak of the LH surge averaged 65 h (range 56-72 h). The period of oestrous behaviour coincided with the acrophase of the LH surge and lasted for 22 h (12-28 h). Ovulations occurred 21 (16-24) h after the LH peak and 7 (2-12) h after the end of oestrus.