The effect of melatonin on the peripheral concentrations of LH and progesterone post-oestrus and on conception rate in ewes

Abstract

Previous studies have shown that for Scottish Blackface ewes kept under a natural photoperiod and exposed to the ram the daily administration of the indoleamine melatonin from June onwards advanced the breeding season and appeared to increase ovulation rate and subsequent litter size (Wigzell et al., 1986). In the primate, exposure to melatonin has been shown to stimulate progesterone production by the corpus luteum in an in vivo perfusion system (Webley & Hearn, 1987). Similarly melatonin administered at physiological concentrations stimulated progesterone production by bovine and human granulosa cell cultures (Webley & Luck, 1986).The present experiments were carried out to determine:-(a) whether or not melatonin enhances progesterone production and thereby the establishment of pregnancy and embryo survival in the ewe.(b) whether melatonin acts directly on the corpus luteum or indirectly via increased activity of the hypothalamic GnRH pulse generator.(c) whether or not the presence of the ram in the immediate post-oestrus period alters the endocrine status of the ewe and thereby influences conception.