Differences in onset of oestrus in Romney ewes has been observed between locations at similar latitudes in the North Island. Two experiments compared source of ewes and rams, and time of transfer of ewes between locations on the onset of oestrus in Romney ewes. In Expt 1, groups of 30 ewes were interchanged between Wanganui and Takapau on 14 Nov, 5 Dec and 8 Jan. The next day these ewes plus 30 local ewes were joined with 3 Poll Dorset rams. There were no effects of ewe source but ewes at Takapau joined on 15 Nov, 6 Dec and 9 Jan had earlier onsets-of-oestrus than ewes at Wanganui (P<0.05 to P<0.01). Ewes joined on 15 Nov and 6 Dec at Wanganui had a later (P<0.01) onset of oestrus than ewes joined on 9 Jan. In Expt 2, 60 ewes and 3 Poll Dorset rams were interchanged between Wanganui and Poukawa on 13 Nov. These ewes plus 60 local ewes were randomly divided in half and recombined to form 2 mixed groups which were joined with 3 Poukawa or 3 Wanganui Poll Dorset rams. Onset of oestrus was earlier at Poukawa (P<0.001) and for ewes joined with Wanganui rams (P<0.001) but there were no effects of ewe source.
Proceedings of the New Zealand Society of Animal Production, Volume 52, , 161-164, 1992
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