The effect of exposure to oestrous ewes on rams' sexual behaviour, plasma testosterone concentration and ability to stimulate ovulation in seasonally anoestrous ewes.

Previous research has shown that the proportion of seasonal anoestrous ewes that ovulate in response to the introduction of rams ('ram effect') is dependent upon pheromonal and sexual behavioural stimuli emitted by the rams. Close contact with oestrous ewes is likely to increase the rams' libido and level of testosterone secretion, which in turn has been suggested to positively influence the production of pheromones. Thus, the sexual stimulation of rams could be used to improve the efficacy of the 'ram effect'. In the present experiment, 272 ewes were introduced (1) to rams without recent experience of oestrous ewes, (2) to rams recently exposed to oestrous ewes, (3) and (4) to oestrous ewes and rams with or without recent experience with oestrous ewes, or (5) remained isolated from rams. Serum testosterone concentration of rams was elevated equally (P<0.05) when oestrous or anoestrous were introduced. Exposure to oestrous ewes before or after introduction increased (P<0.05) the various measures of ram sexual behaviour directed towards anoestrous ewes. However, there was no statistical evidence that increased sexual activity resulted in an improvement in the ability of rams to stimulate ovulation in anoestrous ewes.