Induction of luteolysis in the mare with a prostaglandin analogue

Five mares were administered 0.5 to 2.0 mg of a prostaglandin analogue, RS 9390 (Syntex), during nine estrous cycles in February and March. Luteolysis as measured by peripheral plasma progesterone occurred in four cycles, transitory luteolysis following 0.5 mg RS 9390 in two cycles, while functional corpora lutea were not present in three cycles. In 8 out of 9 of these cycles the mares returned to estrus 1.5 to 5 days following treatment. It appears that RS 9390 can be used as a regulator of cycle length in mares.