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

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Abstract
Seventy-two Hampshire-cross western ewes were randomly allotted into 8 groups of 9 ewes each. Each group received 1 of the following treatments: (1) control; (2) 1 injn. of 500 IU of PMS; (3) 5 injns. of 30 mg. of progesterone at 3-day intervals; and (4) 5 groups received, respectively, 1, 2, 3, 4, and 5 injns. of 30 mg. of progesterone at 3-day intervals followed by an injn. of 500 IU of PMS 3 days after the last injn. of progesterone. The ewes were checked for estrus during treatment and for 10 days after end of treatment. Ewes showing estrus were bred and slaughtered 3 days later. Ewes which did not come into estrus within 10 days after end of treatment were slaughtered. None of the control ewes came into estrus during the exptl. period, and none had ovulated. None of the ewes receiving PMS alone came into estrus, but all had ovulated. Four of the 9 ewes receiving only progesterone came into estrus and ovulated. All ewes in the group receiving 5 injns. of progesterone and then PMS came into estrus and had ovulated. Ewes receiving from 1 to 4 injns. of progesterone prior to PMS had ovulated, but not all of the ewes came into estrus in any of these groups. The highest percentage of ewes came into estrus in the groups which had received progesterone for the longest period of time. 49% of the ova recovered from all groups were fertilized.