Published online by Cambridge University Press: 27 March 2009
Section 1
1. A total of 189 ewes, of various breeds and crosses were used in slaughter experiments conducted in anoestrum during 1953–6. The ewes were of mixed ages, and included four lambs, aged 52–71 days.
2. Ewes received P.M.S. in different combinations with progesterone to induce co-incident oestrus and ovulation. Progesterone was employed in three forms, as a solution in oil, as a micro-crystalline suspension and as fused pellet implants. One hundred ewes were injected with the oil solutions, eighty-five with the suspensions and four received the pellet form of the hormone.
3. The percentage of ewes that came in oestrus (oestrous response) was higher in those treated for a 5-day period than in those treated for a 3-day period with progesterone in oil P.M.S. being administered 2 days after the final progesterone injection. The oestrous response in ewes receiving progesterone over a 13-day period was no higher than in those treated over 5 days.
4. 172 ewes' tracts were examined for ovulations. In those sheep (excluding the four young lambs) which came in oestrus, all had ovulated. Ovulation was apparently inhibited in some ewes which received progesterone in suspension form. The ovulation rate following treatment with 700 i.u. whole serum P.M.S. was higher than that where 750 i.u. purified serum was employed.
5. Forty-one of the ewes which came in oestrus were slaughtered 41–120 hr. after estimated onset of oestrus. Seventy-six of the ninety-two ova shed by these animals were recovered. 81·3% of recovered ova were cleaved. Of thirty-four ewes slaughtered 61–120 hr. after oestrus, thirty-two (94·1%) yielded one or more apparently normal fertilized ova. There was no evidence that fertility in the Suffolk rams employed in matings decreased to the point where it might affect conception in out-of-season breeding.