Author
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Vanraden, Paul |
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Sanders, Ashley |
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Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 11/21/2001 Publication Date: N/A Citation: N/A Interpretive Summary: Crossbreeding can increase health and efficiency by introducing favorable genes from other breeds, relieving inbreeding depression, and maintaining the gene interactions that cause heterosis. However, few dairy cattle in the US are crossbred because purebred Holsteins are preferred for their high milk production. Current USDA-DHIA genetic evaluations consider data from different breeds separately, and crossbred cows are excluded unless identified as part of a breed association "grading-up" program. This strategy avoids biased evaluations within breeds but provides no evaluations for crossbreds and no method of making unbiased comparisons across breeds. Objectives were to estimate heterosis, and recombination losses (resulting from the disruption of favorable within-breed gene interactions), and to predict the net economic merit of each breed or breed cross. Estimates of heterosis were 3.4% for milk yield, 4.4% for fat yield, and 4.1% for protein yield. Heterosis for somatic cell score was not significant. Estimated heterosis for productive life was 1.2%. Recombination effects were not well estimated and small gains, not losses, were observed. Protein yield of Brown Swiss x Holstein cows equaled that of purebred Holsteins. Fat yields of Jersey x Holstein and Brown Swiss x Holstein crossbreds slightly exceeded that of Holsteins. With cheese yield pricing and considering all merit index traits, profit from these crosses exceeded that of Holsteins for matings at breed bases. For elite matings (top sires and/or dams within breed) however, Holsteins were favored because the range of evaluations is greater in the Holstein breed. A combined national evaluation of data for all breeds and crossbreds may be desirable but would require an extensive programming effort. Technical Abstract: Heterosis and breed differences were estimated for milk yield traits, somatic cell score (SCS), and productive life (PL), a measure of longevity. Yield trait data were from 10,442 crossbreds and 140,421 purebreds born since 1990 in 572 herds. Productive life data were from 41,131 crossbred cows and 726,344 purebreds born from 1960 through 1991. The model for test day yields and SCS included effects of herd-year- season, age, lactation stage, regression on sire's predicted transmitting ability, additive breed effects, heterosis, and recombination. The model for PL included herd-year-season, breed effects, and general heterosis. All effects were assumed to be additive, but estimates of heterosis were converted to a percentage of the parent breed average for reporting. Estimates of general heterosis were 3.4% for milk yield, 4.4% for fat yield, and 4.1% for protein yield. Recombination effects were not well estimated and small gains, not losses, were observed in later generations. Heterosis for SCS was not significant. Estimated heterosis for PL was 1.2% of mean productive life. Protein yield of Brown Swiss x Holstein crossbreds (0.94 kg/d) equaled that of purebred Holsteins. Fat yields of Jersey x Holstein and Brown Swiss x Holstein crossbreds (1.14 and 1.13 kg/d, respectively) slightly exceeded that of Holsteins (1.12 kg/d). With cheese yield pricing and considering all traits, profit from these crosses exceeded that of Holsteins for matings at breed bases. For elite matings, however, Holsteins were favored because the range of evaluations is greater. A combined national evaluation for all breeds and crossbreds may be desirable but would require an extensive programming effort. Credit for heterosis should be given when considering animals for crossbred matings. |
