Seasonal variations in sexual activity and endocrine changes associated with follicular maturation and development in the Peulh ewe

Annual variations in sexual activity (oestrus and ovulation) and in the endocrine balances which govern follicular maturation and ovulation (the ovarian hormones progesterone and oestradiol-17β, and the pituitary hormones FSH, LH and PRL) were studied in the Peulh ewes of Niger. It was found that two types of disturbances in ovarian function limited the fertility of ewes in semi-arid environment: (a) persistent corpora lutea which occurred in 14% of animals and affected 2.2% of oestrous cycles in the course of the year. Their appearance coincided with increasing humidity (in June and July) or daily temperature (December to April); and (b) seasonal anoestrus, observed in 67% of animals from December to April, and coinciding with maximum daily temperatures. These ovarian anomalies were associated with a weak endogenous rhythm of LH secretion without any change in feedback from the ovarian steroids progesterone and oestradiol-17β on the hypothalamic-pituitary axis. A study of seasonal variations in levels of the gonadotrophic hormones indicated that there may be a weaker than usual dependence between the ovary and the pituitary during periods of anomalous sexual activity in Peulh ewes. The results presented suggest that both types of ovarian dysfunction observed in certain Peulh ewes may reflect poorer adaptation to the semi-arid climate. (author). 54 refs, 8 figs, 3 tabs