The use of synthetic prostaglandin analogue to induce oestrus in mares.

A clinical trial involving 359 mares was conducted to ascertain the clinical value of a synthetic prostaglandin analogue (fluprostenol, ICI-81,008) structurally related to PGF2oc for treating mares in prolonged dioestrus. Some 263 mares (73.3%) displayed oestrus within 5 days of a first intramuscular injection of 250 mug fluprostenol and, of those mares later examined for pregnancy, 108 (40%) were found to have conceived during the first induced oestrus. A further 21 mares (8%) cycled normally and conceived to services during the second oestrus. Most (80.3%) of the plasma samples obtained from 242 mares prior to treatment showed a progesterone concentration greater than 1 ng/ml, thereby indicating the presence of functional luteal tissue in the ovaries. The results support earlier observations that most non-pregnant mares which fail to cycle during the breeding season are in a state of prolonged dioestrus rather than anoesturs.