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Journal of Dairy Science Vol. 79 No. 3 487-494
© 1996 by American Dairy Science Association ®
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Estimates of Genetic Trend for Yield Traits of the Registered Jersey Population

A. H. Nizamani 1 and P. J. Berger 1

1 Department of Animal Science, 239 Kildee Hall, Iowa State University, Ames 50011

Data for American Jersey cattle f?om 1960 to 1990 were used to study genetic progress achieved by four paths of selection (sires of bulls, dams of bulls, sires of cows, and dams of cows). Possible methods of obtaining optimal genetic gain for the breed were suggested by the analysis. The generation interval by year of birth for parents of AI bulls was greater from 1975 to 1984 than for most recent 5 yr (1983 to 1987) because previously the use of old proven bulls was greater. Sires of bulls tended to have a longer average generation interval (9.3 yr) than the more nearly optimal interval reported in the literature for AI populations (7.0 yr). Selection differentials for the last 5 yr were larger than the average over all years for milk yield, fat yield, protein yield, and fat percentage. More intense selection for sires of bulls gave a larger increase in PTA over time than did other paths of selection. When all paths of selection were combined, estimated annual genetic change for the Jersey breed was greater from 1983 to 1987 than from 1960 to 1987 for milk yield, fat yield, protein yield, and fat percentage. Potential genetic response from the sires and dams that were available to produce sons was greater than the response from parents actually used. Therefore, better sires and dams were available for genetic enhancement of their progeny than those actually used to produce young sires and replacement females.

Key Words: generation interval • Jersey • genetic trend • selection differential

Submitted on August 18, 1995
Accepted on November 27, 1995




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