Mature Romney ewes were involved in three experiments at Flock House Agricultural Centre and Limestone Downs (near Raglan) to identify factors affecting the percentage of ewes pregnant to mating in November and December following treatment with CIDRs and PMSG. Dorset rams were no better than Romney rams for mating and increasing the ram percentage from 10% to 15% failed to overcome the low conception rate of 50-65%. Rams that had been used for mating 11 days previously increased the percentage of ewes pregnant. Ewes previously lambing in autumn had only a 4.8% increase in ewes mated and pregnant compared with ewes previously lambing in spring. Despite the reuse of CIDRs reducing the percentage of ewes mated by 6.1% it was still economical to reuse CIDRs. There was a consistent increase in ewes pregnant and multiple pregnancies with increasing dose of PMSG. By contrast live weight had no effect on the reproductive performance of ewes except for those ewes less than 40 kg live weight. Regulin implants failed to overcome the low conception rate of ewes mating following treatment with CIDRs and PMSG in December.

T, Inoue, IM Brookes, TN Barry, and A John

Proceedings of the New Zealand Society of Animal Production, Volume 49, , 221-224, 1989
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