The use of progesterone and serum gonadotrophin (P.M.S.) in the control of fertility in sheep. I. The hormonal augmentation of fertility in the ewe during the breeding season

Abstract

1. Over four breeding seasons (1952–6) field trials, involving a total of 2504 treated and control ewes of nine breeds (Romney, Clun, Suffolk, Cheviot, Lincoln, Welsh Mountain, Ryeland, Southdown and Hampshire) were conducted in an attempt to increase flock fertility by injections of p.m.s. hormone. The hormone employed was in three forms of preparation: purified, freeze-dried and whole serum. Dosage levels from 250 to 1000 i.u. were injected subcutaneously.2. There is no evidence that the treatment affected the ability of the ewe to conceive.3. A significant increase in fertility was induced by treatment. The extent of the increase apparently depended on the dosage level and form of p.m.s. employed, and was found to be affected by the normal fertility status of the sheep undergoing treatment. At any given dosage level of p.m.s. the increases induced by treatment were greatest where flock fertility was very low.4. When used at comparable dosage levels, whole serum tended to be more effective in inducing superfertility than freeze-dried or purified serum. Freezedried serum tended to be more effective than purified serum.5. 1047 injected sheep that conceived to service at the treatment oestrus produced 1898 lambs (1·81 lambs per ewe); 997 control ewes that conceived at the same time produced 1506 (1·51 lambs per ewe).