The influence of the introduction of rams on the incidence of oestrus in Merino ewes.

Abstract

Two series of observations were carried out on the effect of the presence of the ram on the incidence of oestrus in ewes. In each series a group of Merino ewes was run continuously with vasectomized rams (the continuous group) and another group (the changing group), the ewes of which had been held separate from rams, was joined with the rams for a period of one month only, fresh ewes having been introduced each month. Each series of observations occupied a period of 12-15 months. In all except the spring months most of the ewes of both the continuous group and the changing group exhibited oestrus. During the spring months of one year, 1942, most of the ewes of the changing group exhibited oestrus but many of those in the continuous group failed to do so. During the spring months of the other year, 1943, most of the ewes of the changing group failed to exhibit oestrus as well as most of those of the continuous group, but whereas the proportion which exhibited oestrus did not fall below 30 per cent. in the changing group, it fell as low as 5 per cent. in the continuous group. The differences between the continuous group and the changing group in the proportion of ewes which exhibited oestrus during September and October 1942, and October 1943, are significant at the 1 per cent. level of probability, and that during August 1942 is significant at the 5 per cent. level. These significant differences in the behaviour of the ewes must be attributed to the difference in their previous association with rams.