Recent advances in equine reproduction.

Mares rarely ovulate in winter; ovulation is induced by increase in daylight length. Ova accumulate in the oviducts of unserved mares. During pregnancy, corpora lutea accumulate; all regress together at mid pregnancy. Plasma progesterone levels rise and oestrogen levels fall towards the end of pregnancy. Methods are available for early termination of pregnancy and for induction of parturition. Pregnancy can be diagnosed efficiently by rectal examination, and by immunological assay of pregnant mare serum gonadotrophin. Service at the foal heat is associated with an increased prevalence of early embryonic death; twinning is the commonest single cause of abortion. Spontaneous prolonged dioestrus is common in summer but may be effectively treated. Bacterial endometritis may result mainly from secondary pathogenic activity by organisms of the normal uterine flora; diagnosis by endometrial smear examination is accurate and methods of treatment have improved. The virus of horse pox has been identified, and the occurrence of equine infection with Mycoplasma has been confirmed. In the male, recent work has emphasized that reproductive function is seasonal. The presence or absence of an undescended testis can now be accurately determined.