Induction of Estrus and Ovulation in Anestrual Ewes by Use of Progesterone and Pregnant Mare Serum

Abstract

Anestrual ewes were injected with PMS alone, progesterone alone and progesterone for various periods followed by PMS in late May and June, and the incidence of estrus, ovulation, and fertilization was studied. None of the control ewes came into estrus nor had any ovulated during the experimental period. Injecting anestrual ewes with 500 IU of PMS alone resulted in ovulation but was not accompanied by estrus. When progesterone was injected in approximately physiological amounts for a period of 15 days prior to PMS, synchronous estrus and ovulation occurred in all ewes. Treatment with progesterone alone for a period of 15 days resulted in synchronous estrus and ovulation in four out of nine ewes. Ova ovulated in anestrual ewes by PMS injection following progesterone treatment are fertilizable. Estrus induced by this treatment was approximately of normal duration, i.e., the average duration in this study was 33.6 hours.