Effects of Production, Season, Age of Cow, Days Dry, and Days in Milk on Conception to First Service in Large Commercial Dairy Herds

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Abstract
Effects of management and environmental factors on reproductive performance were evaluated as part of a fertility experiment in 4 large commercial dairy herds. The herds were selected because they used routine herd health programs, kept complete reproduction records on all cows, were enrolled in Dairy Herd Improvement, and would follow the protocol of the experiment. Only data from 1st services following parturition were used, and conception was determined by rectal palpation. Information on over 2800 experimental breedings was collected during 13 mo. Percentage conception to 1st service was not affected by milk production during current or previous lactations. Cows with higher production during current or previous lactation had longer intervals to 1st service. Previous days dry did not affect conception or interval to 1st service significantly. Conception was less for cows with less than 50 days to 1st service (32%) than for cows with over 50 days to 1st service (49-57%). No differences were found among 10-day intervals to 1st service of over 50 days. Cows in 3rd and later lactation had lower reproductive performance than cows in 1st or 2nd lactation. Month of breeding did not affect conception significantly but did affect interval to 1st service. No seasonal trends were apparent. Differences among herds were significant for both conception and interval to 1st service.
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