The use of progesterone and serum gonadotrophin (P.M.S.) in the control of fertility in sheep. II. Studies in the extra-seasonal production of lambs

Abstract

Section 11. 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.

Influence of the Induction of Breeding Activity in Anoestrous Sheep on the Levels of Some Chemical Constituents of Uterine Washings

“…(Gordon, 1958;Allen & Lamming, 1960), but the reasons for the failure of behavioural oestrus in these small groups of sheep are not understood. It has been shown in similar groups of sheep that the fertilization rate of maiden sheep which mated at induced oestrus was usually high (up to 88 %) but in lactating sheep it was low (0 %) (Allen & Lamming, 1959, 1960.…”

“…It would seem, therefore, that there is some additional factor which interferes with conception and implantation in the lactating sheep. Gordon (1958) suggested that there was a failure of implantation in the lactating sheep and showed that fertility was markedly improved if the animals were mated at the oestrus following an induced ovarian cycle which thus simulated the 'silent heat' at the beginning of the normal breeding season. Allen & Lamming (1960) reported the presence of spermatozoa within the zona pellucida of ova recovered after the first induced oestrus but an absence of fertilization.…”

“…Conception rate was higher in treated maiden sheep than in treated lactating sheep possibly due to a failure of fertilization (Allen & Lamming, 1960) or implantation (Gordon, 1958 (Heap, 1962).…”

“…Investigations have been reported on the use of progesterone-pregnant mares' serum (pms) to induce breeding activity of anoestrous sheep (Dutt, 1952(Dutt, , 1953Robinson, 1952Robinson, , 1954Gordon, 1958;Allen & Lamming, 1960). Conception rate was higher in treated maiden sheep than in treated lactating sheep possibly due to a failure of fertilization (Allen & Lamming, 1960) or implantation (Gordon, 1958 (Heap, 1962).…”

Quantitative Studies of the Interaction Between Progesterone and Pregnant Mare Serum on Ovarian Function in the Ewe

“…Pregnant mare serum has been used to increase fecundity in the ewe during the breeding season (Robinson, 1951; Wallace, 1954;Gordon, 1958a), and to augment fertility during anoestrus (Dutt, 1953; Robinson, 1954;Gordon, 1958b). During the breeding season, pms is given on the 12th to 14th day after oestrus, when the production of progesterone by the corpus luteum may be expected to be declining or about to decline (Edgar & Ronaldson, 1958).…”