Studies on the number of ewes joined per ram for flock matings under paddock conditions. I. Mating behaviour and fertility

Abstract

In a series of six experiments rams were joined either singularly or in groups to varying numbers of ewes so that the number of ewes joined per ram varied between 25 and 100. Under the conditions of these experiments, decreasing the number of ewes joined per ram was associated with more rams serving each oestrous ewe, a greater proportion of ewes served during the first 2 weeks of joining, less ewes remaining unserved at the end of a 6 week joining period, and higher fertility (the proportions of ewes lambing and ewes twinning to ewes joined). A highly significant interaction (P < 0.001) between number of ewes joined per ram and ram age was found. Joining 25 ewes per ram gave higher fertility than 50 ewes per ram when 1½ -year-old rams were used, but similar fertility with 3½–5½-year-old rams. Older rams were more fertile than 1½-year-olds when joined at 50 ewes per ram, but not at 25 ewes per ram. These findings are discussed in relation to other factors that may influence the effect on flock fertility of varying the number of ewes joined per ram.