Induction of early breeding in sheep by standard and modified progestagen-PMS treatments

Abstract

SUMMARY The oestrous response and subsequent lambing performance of 264 sheep was studied after treatment with intravaginal sponges and PMS during July (period of late anoestrus). Four progestagen treatments were employed, each in combination with one or other of four dose levels of PMS (0, 250, 500 and 750 i.u.) given at pessary withdrawal; the sixteen resultant treatments were applied in each of seventeen flocks. Modification of standard ‘Cronolone’ (9α-fluoro-11β-hydroxy-17α-acetoxy-progesterono; G. D. Searle) pessaries to ensure thorough dispersion of the compound resulted in a significantly higher mating response and lambing outcome. The highest lambing outcome followed the use of 500 i.u. PMS. The onset of heat, relative to progestagen withdrawal, was affected both by progestagen treatment and PMS dose level. The conception percentage was highest in sheep which were bred on the second day after treatment. The implications of the data, in explaining some previous results with standard ‘Cronolone’ sponges, are briefly discussed.