Mating activity and reproductive performance in Merino flocks where ram percentages are 1.0, 0.5 and 0.25

Abstract

Mature Merino rams were joined at rates of one ram to 100 ewes (1.0%), one ram to 200 ewes (0.5%) and one ram to 400 ewes (0.25%) in paddocks at Richmond, New South Wales. Fresh rams were introduced each day of joining and mating activity was measured and behaviour was studied by direct observation. Thirty-eight days after the removal of entire rams, the ewes were slaughtered and reproductive tracts were collected and examined. As ram percentage fell so also did services per ewe (4.3 to 2.2), number of ewes that mated (6.2 to 3.3/d) and the percentage of ewes that became pregnant (88.8 to 60.4%). Ram service activity remained constant as the number of ewes per ram increased. There were increases in the number of oestrous ewes in physical contact with and crowding the rams and in the number of ewes returning to be served in the second period of joining. The study suggests that the percentage of mature Merino rams joined with mature Merino ewes should not be less than one, because below this value, reproductive performance declines. The decline may be due to oestrous ewes crowding around the ram, thus preventing rams from increasing service activity thereby reducing services per ewe, ewes mated and ewes pregnant.