Synchronization of œstrus in ewes with Provera sponges/PMSG, prostaglandin F2α or the prostaglandin analogue, ICI 80996, and fertility following natural mating or artificial insemination

: Following the synchronization of oestrus with different treatments during the breeding season, the fertility of naturally-mated ewes has been compared to that of ewes artificially inseminated with fresh semen. The following treatments were used: I. sponges impregnated with progestagen (50--60 mg of medroxyprogesterone acetate) left in situ for 14 days and an i.m. injection of 500 IU of PMSG at sponge withdrawal; II. injections of prostaglandin F2 alpha (dose: 15 mg/injection) at intervals varying from 9 to 14 days (see tables); III. injections of the prostaglandin F2 alpha analogue, ICI 80996 (dose: 100 micrograms/injection), with the same time intervals as in treatment II. Lambing rate and prolificacy after natural service at the induced oestrus was 55 and 140 p. 100, 32.5 and 153 p. 100 and 60 and 133 p. 100 for ewes receiving treatments I, II or III, respectively, compared to 62.5 and 120 p. 100 for the untreated controls. Double artificial insemination (AI) 48 and 58 h after the sponge/PMSG treatment resulted in a lambing rate of 25 p. 100 and a prolificacy of 133 p. 100. The lambing rate and prolificacy of ewes inseminated 58 and 68 h after the final injection of PGF2 alpha or ICI 80996 were 27.8 and 149 p. 100 and 45.5 and 165 p. 100, respectively. Single AI 55 h after sponge withdrawal gave a lambing rate of 37.8 p. 100. The lambing rate of ewes inseminated 56 h after the final ICI 80996 injection was higher (54.8 p. 100) than that of ewes inseminated at 60 h (37.5 p. 100) or 66 h (30.8 p. 100). However, two inseminations 56 and 66 h after the final ICI 80996 injection gave an even more elevated lambing rate (61.9 p. 100). These results demonstrate that ICI 80996 can successfully control oestrus in the ewe during the breeding season, thus offering an alternative to sponges/PMSG and that the fertility subsequent to both natural mating and AI is equivalent to that of the controls.