Biochemical-morphological modifications of platelet membranes during pregnancy-induced hypertension

Progesterone profiles were monitored in goats housed in single (n = 9) or group (n = 14) pens during winter (JJA) and spring (SON). Normal cycles (n = 97) were < or = 30 days. Extended cycles (n = 45) were > 30 days and, except for one cycle with a persistent corpus luteum, had periovulatory periods of 10 to 20 days (n = 29) or averaging 65.1 days in length (n = 15), mostly characterised by recurrent oestrus and/or occasional transient rises in progesterone. The proportion of normal cycles occurring in winter was 87.5% (28/32) and 77.7% (42/54) for goats in single and group pens respectively, falling to 62.5% (15/24) and 37.5% (12/32) respectively in spring. The distribution of normal vs extended cycles according to season was significant (P < 0.05, single; P < 0.001 group pens). Goats housed communally experienced a greater fall in the percentage of normal cycles in spring, possibly due to increased stress associated with group feeding. Within each season, however, housing per se did not influence the distribution of normal vs extended cycles. For normal cycles, Harvey's Analysis of Variance showed that season was significantly associated with length of the periovulatory period (3.99 days (JJA) vs 5.79 days (SON); P < 0.001), oestrus detection rate (87% (JJA) vs 55% (SON); P < 0.01) and oestrus duration (1.94 days (JJA) vs 1.13 days (SON); P < 0.05). In contrast, luteal phase length was not affected by season, but was significantly associated with housing (16.93 days (single pens) vs 18.32 days (group pens); P < 0.01). The reduction in ovarian activity observed in spring may reflect a seasonal reduction in fertility, possibly linked with increasing temperature and photoperiod.