Effect of intravaginal progestagens on oestrus activity of Mutton Merino ewes.

Seven groups of SA Mutton Merino ewes, representing seven different stages in the oestrous cycle i.e., day 0 (ovulation), 2, 4, 6, 8, 10 and 12, were treated with medroxy progesterone acetate impregnated intravaginal sponges for a period of 12 days. Time intervals between sponge removal and the commencement of oestrus and the duration of the oestrous period were monitored. Blood samples were collected at regular intervals throughout the experimental period for determination of the plasma progesterone and LH concentrations. A significant difference (P<0,05) in the average interval from sponge withdrawal to the commencement of oestrus, was found only between ewes treated on day 0 (Group 1) and day 6 (Group 4). Although results indicated a gradual increase in the length of oestrus as the sponge stage advanced, the treatment did not affect the time of maximum LH concentration (12 h after commencement of oestrus) significantly. According to the plasma progesterone concentration, exogenous progestagen administration had no significant effect on the development, progesterone production and degeneration of the corpus luteum.