Ram-ewe contact when ewes are in anoestrus may reduce the ram`s ability to stimulate oestrous activity in ewes. Conversely, oestrus ewes increase the ram’s ability to stimulate ewes, possibly by increasing plasma testosterone concentration (T). On 25 November, 400 Romney ewes and 12 Dorset teasers were each randomised into 2 groups. One group of ewes and rams were joined while the others were isolated from the opposite sex. On 14 January (day 0) half of each group of ewes was joined for 35 days with either rams which had been previously exposed or not exposed to ewes, and mating marks were recorded each week. In a second experiment, 16 Romney rams were introduced (day 0) to oestrus or non-oestrus ewes and bled on days -1, 0, 2 and 5, and the blood plasma analysed for T. Rams not previously exposed to ewes stimulated more ewes to exhibit oestrus by day 35 than rams previously exposed to ewes (46% vs. 30%; P<0.01). Ewes previously exposed and those not exposed to rams responded similarly to ram stimulation, and by day 35 there was no difference in percentage of ewes mated. Both oestrus and anoestrus ewes increased T in rams on day 0. On day 2, T had returned to day -1 levels for rams with anoestrus ewes but increased further in rams with oestrus ewes (0.67 vs. 2.34 ng/ml; P<0.05).
Proceedings of the New Zealand Society of Animal Production, Volume 58, , 178-180, 1998
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