Since 1969, 36 sire breeds have been evaluated for topcross performance in a series of experiments (Cycles) in the Germ Plasm Evaluation (GPE) Program. In Cycle VII, the 7 most prominent U.S. beef breeds (3 British breeds: Angus, Hereford, Red Angus; and 4 Continental European breeds: Simmental, Gelbvieh, Charolais, Limousin), comprising 83% of U.S. breed association registrations, are being evaluated. In the 1970’s, Continental breeds had greater growth rates and were heavier atweaning, yearling, and maturity. Today British breeds in the U.S. are comparable to Continental breeds for these traits. Steers of Continental sire breeds still excel in retail product yield (%), but those of British sire breeds excel in marbling, an important component of U.S. carcass value, and enjoy a slight (P<.05) advantage in tenderness over Continental breeds. Since 1973, current expected progeny differences (EPD) from breed associations and GPE data have been used to estimate breed differences annually. Since 1993 adjustment factors have been calculated to be added to the EPD of 16 breeds to calculate across-breed EPD for growth traits. Multi-breed genetic evaluations are being explored by scientists at three U.S. Universities (Cornell, Georgia, Colorado State). In Cycle VII, DNA was obtained on all sires, dams, and progeny produced in the F1 cross generation, grand progeny, and great-grand progeny to provide for parentage determination, and for identification and validation of quantitative trait loci (QTL). Alternative mating plans are being explored to include additional breeds (> 15), to provide more efficient estimates of direct and maternal breed and heterosis effects, and to facilitate use of QTL in multi-breed genetic evaluations. Our review describes how the U.S. beef cattle breeding industry continues to use the evolving GPE results, and how the Cycle VII DNA samples will be used to provide progressively more accurate predictors of sire EPD on a within-breed or between-breed basis, through groups such as the National Beef Cattle Evaluation Consortium. The opportunities for U.S. cattle breeders arising from new breeding technologiesare described, including the potential for similar opportunities to be used in the New Zealand beef industry.

LV, Cundiff, RM Thallman, van LD Vleck, GL Bennett, and CA Morris

Proceedings of the New Zealand Society of Animal Production, Volume 67, Wanaka, 9-17, 2007
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