Induction of oestrus and fertility in the anoestrous ewe with hormones and controlled lighting and temperature

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Abstract
A program consisting of 14 daily progesterone injections (10 mg) followed by single injection of pregnant mare''s serum gonadotropin (500 IU) and estradiol-17.beta. (30 .mu.g), along with controlled temperature (18-20.degree. C) and lighting (10 h light/24 h), was applied to 60 anestrous ewes between late May and early Aug. to induce reproductive activity. Breeding started within 24 h of the estradiol injection and 80.0% of the ewes conceived at the induced estrus. Dorset ewes had higher conception (95.2 vs. 71.8%) and prolificacy (1.74 vs. 1.52 fetuses/ewe) rates than did crossbred Suffolk ewes. Plasma progesterone concentrations during progesterone administration were significantly higher than those found during anestrus, and were generally lower in ewes which did not conceive than in those which did. The plasma progesterone data indicated that ovulation occurred in most of the ewes which were not pregnant at 90-100 days, and that many were initially pregnant but then lost the conceptus.