Treatment of post-partum anoestrous dairy cows with progesterone, oestradiol and equine chorionic gonadotrophin

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Abstract
Anoestrus in lactating dairy cows at the start of the breeding season is a major form of reproductive wastage for seasonal dairy production based on pasture. The objective of this study was to compare the reproductive performance of anoestrous cows that were treated with a combination of progesterone, oestradiol and equine chorionic gonadotrophin either 10 days before (T-10, n = 219) or 16 days after (T+ 16, n = 229) the start of the breeding season. A higher percentage of cows in the T-10 group were detected in oestrus and inseminated during the first 6 days of breeding than those in the T+16 group (69.4% v. 26.2%, p < 0.001). However, the percentage of cows detected in oestrus by Day 16 was similar between the two treatment groups (T-10 v. T+16; 77.7% v. 76.7%). There was no difference between treatment groups in conception rate to the first (51.2% v. 59.0%) or the second insemination (50.8% v. 57.6%), in pregnancy rate over the first 49 days (74.0% v. 75.1%), in empty rate (10.0% v. 10.5%) or in the mean day of conception from the start of the breeding season (24.0 v. 25.7 days). These results suggest that, under favourable environmental conditions, treatment of anoestrous cows with the programme used in this trial can be performed 16 days after the start of the breeding season with similar results to that performed 10 days before the start of the breeding season. Further studies are needed to determine if this is the case under different environmental conditions or for other treatment programmes.