Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 18, 2006
Publication Date: May 1, 2007
Citation: Van Raden, P.M., Tooker, M.E., Cole, J.B., Wiggans, G.R., Megonigal Jr, J.H. 2007. Genetic Evaluations for Mixed-Breed Populations. Journal of Dairy Science. 90(5):2434-2441. Interpretive Summary: An all-breed animal model was developed for genetic evaluations of US dairy cattle. Data from individual breeds were combined, and the combined pedigree file included 431,000 crossbred cows. Evaluations from the all- and within-breed systems were highly correlated, and most purebred breeders will not be impacted by the new model. Predicted transmitting abilities will be presented on within-breed bases for purebreds and breed-of-sire bases for crossbreds. Use of crossbred records may increase reliabilities for purebreds, and crossbreds in mixed breed herds will benefit from the use of cows of other breeds as contemporaries. Implementation is expected in May 2007.
Technical Abstract: An all-breed animal model was developed for routine genetic evaluations of US dairy cattle. Data sets from individual breeds were combined, and records from crossbred cows were included. About 1% of recent cows were first generation crossbreds. Numbers of cows with records since 1960 ranged from 10 to 22 million for the six traits analyzed, which were milk, fat, protein, somatic cell score, productive life, and daughter pregnancy rate. Programs were modified to account for general heterosis, to group unknown parents separately by breed, to adjust variances separately by breed, and to adjust data to 36-month age equivalent instead of mature equivalent. Convergence rate of the all-breed model was similar to that of the previous within-breed animal model. Estimated breed differences were similar to those obtained previously from phenotypic breed means or from only the herds containing crossbred cows. Genetic evaluations from the all-breed and within-breed system had high correlations: >0.99 for recent Holsteins and slightly <0.99 for other breeds. Predicted transmitting abilities will be converted back to the within-breed bases for purebred animals and to the breed of sire base for crossbred animals so that most purebred breeders will not be impacted by the change to a multi-breed model. Crossbred animals can be evaluated accurately with the all-breed model. Reliabilities also increase for purebred relatives because of the additional crossbred records and in mixed breed herds because cows of other breeds are additional contemporaries. More research and education may be needed on using the new evaluations in design of breeding programs. Implementation is expected in May 2007.