A note on mating preferences in Rasa Aragonesa rams

Two experiments were conducted to determine whether Rasa Aragonesa rams, a Mediterranean breed, mount ewes randomly or preferentially when presented with a group of 12 oestrous-synchronized ewes during the period of natural seasonal anoestrus. In the first experiment, 12 Rasa Aragonesa ewes were induced into oestrus using intravaginal pessaries. Forty-eight hours after pessary withdrawal, the group of ewes was presented to an aproned ram (to prevent ejaculation) and the time spent by the ram courting and mounting each ewe was recorded. To quantify differences in sexual attractiveness among ewes, a modified Tillbrook test was performed. The procedures were repeated using eight rams. Both the average amount of time spent by rams courting individual ewes (15.4 s, S.E. = 2.9, range of means = 11.7-22.5 s) and the average amount of time that individual ewes were courted by an individual ram (15.4 s, S.E. = 3.5, range of means = 9.7-21.7 s) varied significantly (P < 0.05). In the second experiment, each of 5 rams was presented to a group of 12 oestrous-synchronized ewes. Rams were permitted to court and service ewes over 2 h periods and individual ewes were not removed after being serviced. The number of services per ewe was recorded. Rams differed significantly in the number of ewes serviced. Collectively, these results suggest that mating management techniques should appreciate that minimizing the ram-to-ewe ratio could foster lower fecundity in Rasa Aragonesa sheep.