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Department of Animal Science, Cornell University, Ithaca, NY 14853
ABSTRACT
This was a field study to gain information on fertility of New York dairy herds and factors influencing it. Data were from 125 Dairy Herd Improvement Holstein herds with 9,750 cows. All breedings to milking cows were by artificial insemination. Herds were further selected with equal numbers of small and large herds and free-stall and conventional (stanchion) housing. Conception on first service averaged 50% and the 60 to 90 day nonreturns, 58%. Interval from calving to first service averaged 87 days and days open 116 days. Intervals between first and second service averaged 41 days and between second and third service 40 days. A total of 76 and 89% of all cows were pregnant on the first two and first three services.
Conception declined markedly with increased production when age, herd size, and other variables in the model were not allowed to vary. Cows producing > 907 kg above herdmates were 20.5 percentage units in conception on first service lower than the base group of cows which were 
907 kg below their herdmates in milk production. As age advanced beyond 4 yr, fertility declined for given milk production. As size of herds increased, reproductive efficiency, as indicated by conception rate, declined; however, milk produced per cow increased. Lengths of dry period were not influenced by production or herd size but did increase with age of cow.
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