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Journal of Dairy Science Vol. 57 No. 9 1067-1075
© 1974 by American Dairy Science Association ®
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Genetic Trend Estimators1

R. L. Powell2 and A. E. Freeman

Department of Animal Science, Iowa State University, Ames 50010

ABSTRACT

Five estimators of intraherd genetic trend were compared in 13,615 Holstein first lactations from 220 progeny test herds. The preferred method estimated the trend as minus twice the regression of deviated production on time of freshening within sire-herd subclasses. Estimates of annual intraherd genetic trend from this approach were 82 kg of milk and 1.5 kg of fat. Adjustments for age and merit of sires' mates generally negated each other. Either both or neither adjustment should be used because applying only one will bias estimates of trend. Methods involving deviated records substantially over-estimated genetic trend if the mean from which the records were deviated excluded the sire's progeny. Estimates from two approaches relying on full sisters had the largest standard errors and may be subject to systematic biases. Another approach used estimates of sire merit from a model containing fixed effects of herd-year-seasons and sire groups and random effects of error and sires within groups. Estimates of genetic trend from the intraherd regression of sire breeding value on time of freshening were dependent on proper definitions of groups.

FOOTNOTES

1 Journal Paper J-7780 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project 1053, done in collaboration with North Central Regional Project NC-2, Improvement of Dairy Cattle Through Breeding.

2 Present address: Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, Maryland 20705.






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Copyright © 1974 by the American Dairy Science Association ®.