Control of oestrus and ovulation by progesterone and cronolone administered either intramuscularly or intravaginally and subsequent fertility

Abstract

A factorial test involving 960 cyclic Merino ewes was carried out to compare the effectiveness of two progestagens (progesterone and 17~-acetoxy-901-fluoro-11Phydroxypregn- 4-ene-3,20-dione: Cronolone) administered either by daily intramuscular injection (i/m) or by intravaginal sponge (i/vag) for the control of oestrus and ovulation. Other factors included in the test were dose of progestagen (three doses for each progestagen and method of administration), day of oestrous cycle on which treatment commenced (day 2, 6, 10, or I4), and method of mating (natural service or artificial insemination). An additional 160 untreated ewes were included as controls. Of the 960 ewes which were treated, 677 were detected in oestrus within 5 days after treatment and the onset of oestrus was earlier and more precise after intravaginal than after intramuscular treatment. There were significant effects of method of administration and of dose of progestagen on the number of ewes in which oestrus was controlled, but there were no effects of day of commencing treatment. Overall, treatment depressed fertility to both artificial insemination and natural service. Of the 677 ewes in which oestrus was controlled, 362 (54%) lambed compared with 110 of 160 control ewes (69%). However, two particular treatments, 12 mg/day progesterone by injection and 24 mg Cronolone by sponge, gave lambing performances comparable with that of control ewes. In addition both treatments gave excellent control of oestrus and ovulation.