A study was conducted at the Lincoln University Dairy Farm to investigate factors influencing conception rate (CR). Relative to the planned start of mating date (Day 0), milk progesterone (MP4) concentrations were determined weekly from Day -20 to 0, twice weekly from Day 0 to 42, and then weekly to Day 70 in 666 cows. Trough-like patterns among individual profiles were identified and defined as periovulatory events. Pre-mating ovulatory status was a predictor (P < 0.01) of first service CR (FSCR), with anovulatory cows having a lower FSCR (37.4%) compared with ‘late’ (47.3%) and ‘early’ (56.4%) ovulating cows. In turn, interval from calving to Day 0 was a significant determinant for pre-mating ovulatory status. Oestrus detection was performed to a high standard, even though 5% of the 850 artificial inseminations were coincident with a lack of ovulation. MP4 profiles also indicated that 4% of cows that conceived during the 37-day artificial breeding period subsequently lost these pregnancies. A 2.6% error rate for diagnosing pregnancies on Day 78 was detected, mostly due to incorrectly attributing pregnancies following artificial breeding. Findings indicate the critical importance of managerial strategies that promote a high prevalence of cows having ovulated at least 21 days before mating starts.
Proceedings of the New Zealand Society of Animal Production, Volume 72, Christchurch, 45-50, 2012
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