Effect of the presence of male and female flockmates on reproductive activity in ewes
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Four experiments were carried out to determine the effect of the presence of ewes and rams on the reproductive state of ewes. In Expt 1, the breeding season of ewes kept with a vasectomized ram ended later (April 18 ± 8 days; mean ± sem) than that of ewes isolated from rams (6 March ± 7 days; P < 0.01). In Expt 2, the end of the breeding season was later (5 May ± 6 days; P < 0.05) and the onset of the next breeding season earlier (29 September ± 2 days; P < 0.001) in ewes maintained with rams, compared with ewes isolated from rams (14 April ± 7 days and 1 November ± 2 days, respectively). There was no difference in the timing of, or variation in, reproductive transitions between ewes maintained either as individuals or in groups. In Expt 3, all ewes exposed to artificial short days from the date of the winter solstice and interrupted with 35 long days in spring resumed cyclicity (median date, 7 September; range, 59 days). Most ewes (seven of nine) exposed to short days from the date of the winter solstice and isolated from other ewes did not resume cyclicity in the following 11 months. In contrast, all ewes resumed cyclicity (median date, 19 October; range, 144 days) when exposed to short days but housed in social contact with other ewes that became reproductively active in early September; however, the onset of cyclicity was later than in ewes exposed to long days (P < 0.01). In Expt 4, the number of LH pulses per 6 h in ewes exposed to rams was higher (P < 0.001) and the time of first ovulation earlier (16 August ± 5 days; P < 0.05) than it was in ewes that were isolated from rams and exposed to either oestrous or anoestrous ewes. We conclude that there was a chronic stimulus from rams to ewes that increased the duration of the breeding season and decreased anoestrus. There was no acute effect of introduction of oestrous ewes to anoestrous ewes on LH pulse frequency and time of first ovulation of the breeding season under the natural photoperiod, and the onset of the breeding season of housed anoestrous ewes exposed to a constant photoperiod was advanced by housing them with cyclic ewes. These results highlight a role for social or other animal-related stimuli in seasonal reproduction in ewes.
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