The effect of treating dairy cows with anovulatory anoestrus (n=660) at various intervals post-partum was investigated. Treatment consisted of priming with progesterone using an intravaginal device (CIDR-B) for 6 days, with an injection of oestradiol benzoate 24h after device removal. The mean interval from treatment termination to conception tended to be greater for cows calved less than 3 weeks at diagnosis than contemporaries calved at least 3 weeks (32.8 6.3 vs 23.7 ± 1.1 days; p<0.1). Final empty rate was higher for cows diagnosed and treated within 3 weeks post-partum (39% vs 13%; p<0.001). Survival analysis accounted for the higher empty rate to determine the probability of pregnancy over time. Cows calved less than 3 weeks at treatment had a lower probability of pregnancy than contemporaries calved at least 3 weeks (p<0.01). This study found a negative effect of treating anoestrous cows within 3 weeks post-partum. Further work should define the nature of this problem and the value of delaying treatment until at least 3 weeks after calving.
Proceedings of the New Zealand Society of Animal Production, Volume 57, , 228-230, 1997
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