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Induction of Estrus and Ovulation in Ewes during Their Anestrus Season

Animal Disease Station, U. S. Bureau of Animal Industry, Beltsville Research Center, Beltsville, Md.

Abstract

Estrus may be induced in ewes during their anestrus season by the injection of diethylstilbestrol (stilbestrol). Two milligrams on the first day and one milligram on the second day induced estrus in eleven of twelve animals. Spontaneous estrus did not occur within 20 days after it had been induced with the hormone.

Ovulation was proved by laparotomy to be induced in all of thirteen ewes that had received one or more injections of pregnant mare's serum. Estrus rarely occurred from a single injection or daily injections of P.M.S., but four of six ewes given two doses 16 days apart came into estrus following the second injection, and one became pregnant.

The time factor in the induction and duration of estrus by stilbestrol was neither increased nor decreased by P.M.S., but stilbestrol did appear to have an inhibitory effect on the action of gonadin, since in 7 of 15 instances ovulation was not induced when these substances were injected in combination.