Role of the vomeronasal organ on ram's courtship and mating behaviour, and on mate choice among oestrous ewes

Two experiments were performed to determine the role of the ram's vomeronasal organ (VNO) in courtship and mating behaviour, and in mate choice among different oestrous ewes. In the first experiment, 19 tests were performed, each with one ram and two oestrous ewes, in which courtship behaviour, matings and mountings with ejaculations were registered during 20 min. The rams used in nine tests had the access to the entrance to the VNO obstructed; the other 10 remained untreated (C1 rams). While the total courtship time was not different for both groups of rams, the C1 rams mounted and ejaculated significantly more times than the rams without VNO activity. In the second experiment, the rank preference of six oestrous ewes by untreated and VNO blocked rams was registered in five tests. While in previous articles it is reported that different rams select oestrous ewes in a similar order, in the present experiment rams with or without VNO activity selected ewes in a different order. We conclude that the pheromone stimulus of oestrous ewes determines an increase of ram's sexual performance, and that ewe's pheromones are implicated in ram's mate choice.