PLASMA PROGESTERONE PROFILES AND VARIATION IN CYCLIC OVARIAN ACTIVITY THROUGHOUT THE YEAR IN INDIGENOUS GOATS IN ZIMBABWE

Eleven non-pregnant indigenous goats were bled three times a week from 1 June 1988 to 31 May 1989. They were fed hay ad libitum supplemented by concentrates, and housed indoors in single pens until November when the goats were divided between two large pens. Plasma progesterone profiles were used to calculate cycle length: 73.3% (99/135) of cycles, mean length 22.0 +/- 0.3 days, were classified as normal (N). N cycles had a mean luteal phase of 17.5 +/- 0.2 days followed by a peri-ovulatory period of 4.5 +/- 0.2 days. Cycles greater than 30 days long were classified as extended (E). These had normal length luteal phases followed by basal progesterone for 15.4 +/- 0.5 days (n = 22) or 38.9 +/- 4.1 days (n = 10) before the next cycle, giving cycle lengths of 33.6 +/- 0.7 days and 56.3 +/- 0.9 days, respectively. Four E cycles (mean length 117.0 +/- 30 days) had a persistent corpus luteum followed by basal progesterone of 17.8 +/- 5.6 days in duration. The distribution of N versus E cycles varied between animals and was significantly influenced by season (P < 0.005) and housing (P < 0.005), but not body condition. The proportion of N cycles was highest in the cool, dry winter months from June to August, fell during the hot, rainy months from September to February, and rose again between March and May. The proportion of N cycles was higher for goats housed in single pens, however the effect of season and housing were confounded by the move from single to group pens in November.