Transition management in the mare

The mare is a seasonally polyoestrous long-day breeder with a physiological breeding season lasting from April to October in the Northern hemisphere. The hypothalamic– pituitary–gonadal axis in the mare is subject to a circannual endogenous rhythm that is primarily regulated by day length. Other factors such as environmental conditions, nutrition, age and breed have been shown to influence seasonal reproduction in the mare. Increasing ambient photoperiod in the spring alters the pattern of melatonin secretion. The resulting stimulation of hypothalamic gonadotropin-releasing hormone (GnRH) secretion triggers pituitary follicle-stimulating hormone (FSH) release and follicular growth. Initially, follicles are steriodogenically incompetent, with positive feedback on luteinising hormone (LH) secretion only occurring when a dominant follicle releases sufficient oestrogen to cause an LH surge, resulting in the first ovulation of the year and the end of the transition period ...