Fertility of anoestrous ewes following injection of progesterone and Pregnant Mare Serum (PMS).

Abstract

Experiments are described in which progesterone was used alone and in combination with pregnant mare serum (PMS) in breeding Suffolk, Suffolk crossbred, and Romney Marsh ewes in anoestrus. While oestrus, presumably with ovulation, was induced in a high proportion of ewes treated with the two hormones in combination, lambing percentages were low. Of 20 Romneys treated, 18 were served, but only 5 held to this service. Comparable figures for Suffolks were: 20 treated, 18 served, 7 lambed. The crossbreds gave better results; of 6 ewes treated all were served and 5 lambed. There was some evidence that the conception rate was higher following a complete ovarian cycle. Factors which may be involved in this phenomenon are discussed.