SC-9880-progesterone applications in the induction of early breeding in sheep

Abstract

SUMMARYThe mating response and lambing outcome was studied in 584 sheep in twentyeight farm flocks after treatment with progestagen impregnated intravaginal sponges and PMS during June/July (period of late anoestrus). Each pessary carried a dose of 30 mg ‘Cronolone’ (9α-fluoro-11β-hydroxy-17α-acetoxy-progesterone; SC-9880, G. D. Searle) in finely dispersed form; half the number of pessaries carried an additional dose of 400 mg progesterone. Intravaginal treatment was for 12 days; a single intramuscular injection of 500 i.u. PMS (Burrough's Wellcome) was made at pessary withdrawal. Breeding was by natural service, using 10% rams. The response was 98·8% bred in the 4 days after treatment, 61·2% conceptions in those served and an average of 1·65 lambs/conception. This resulted in the birth, within the period of about 1 week, of 100 ‘early’ lambs for every 100 ewes exposed to rams. The addition of 400 mg progesterone to pessaries or the injection of a dose of 5 mg progesterone at sponge withdrawal did not improve response beyond that found with ‘Cronolone’ alone.

Plasma progesterone concentrations, ovarian and endocrinological responses and sperm transport in ewes with synchronized oestrus

“…This conclusion is supported by the observation of Hawk, Cooper & Pursel (1981) that removal of the corpus luteum in a normal cycle impaired transport of spermatozoa at the ensuing oestrus due to decreased viability. Use of supplementary progesterone after sponge removal failed to ameliorate the situation, which fits the observation of Gordon (1971) that conception rate was unchanged by the injection of 5 mg progesterone at the time of sponge withdrawal.…”

Plasma hormone levels and reproductive behaviour in anoestrous ewes after treatment with progesterone and PMSG

“…Seasonally anoestrous ewes can be induced to show a fertile oestrus by a period of treatment with progesterone or a synthetic progestagen followed by an injection of PMSG (Gordon, 1971;Boland & Gordon, 1973). Saba, Cunningham, Symons & Millar (1975) reported that treatment of ewes with progesterone during July-August induced ovulation, but there was a low incidence of overt oestrus, and Boland & Gordon (1973) concluded that, in the absence of PMSG, progestagen treatments resulted in only a limited ovulatory response with a high proportion of ewes having 'silent' heats.…”