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Effects of Various Factors on Reproductive Efficiency^1,2,

Animal Sciences Department, University of New Hampshire, Durham 03824

ABSTRACT

Records of 370 Holsteins and 223 Jerseys from four university herds were used to study the effects of various factors on the number of services per conception, days from first breeding to conception, and calving interval. Relationships between each of these measures of breeding efficiency and milk production were also estimated. There were differences among herds in breeding efficiency which for the Holstein data ranged from 1.66 to 2.54 services per conception, from 18.5 to 43.5 days from first breeding to conception, and from a 388 to a 419 day calving interval. Similar for the Jersey data were 1.71 to 2.24 services, 18.5 to 39.3 days, and 382 to 405 days. There were differences among years for all measures of breeding efficiency for the Jersey data only. Lactation number had an effect on days from first breeding to conception and on calving interval for the Holstein data. The herd-by-year interaction was significant for all measures of breeding efficiency for the Jersey data. Seasonal effects on breeding efficiency were not evident. There was some indication of a small antagonistic relationship between production and breeding efficiency.

¹ Published with the approval of the Director of the New Hampshire Agricultural Experiment Station as Scientific Contribution No. 723.

² Partially supported by Grant-in-Aid from the Eastern Artificial Insemination Cooperative, Ithaca, NY.

³ Department of Animal Husbandry, University of Thessaloniki, Thessaloniki, Greece.

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