Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 2/25/2008
Publication Date: 7/11/2008
Citation: Powell, R.L., Norman, H.D., Hutchison, J.L. 2008. Breed Composition of the United States Dairy Cattle Herd. Journal of Dairy Science. 91(E-Suppl. 1):7(abstr. T17).
Technical Abstract: Breed composition of the gene pool of all cows (purebred and crossbred) with pedigree data in the USDA national dairy database was summarized by birth year of cow. Partial breed contributions were assigned for individual cows. For cows born in 2005, 1.1% of all genes and 35.1% of genes in crossbreds traced to a female ancestor with breed reported as unknown; i.e., a dam without reported identification information. When a cow and her sire had the same reported breed but her dam’s breed was unknown, the sire’s breed was assigned to the dam, which decreased the percentage of unknown genes to 0.7 for all cows born in 2005 and to 6.7 for crossbreds. The percentage of the national herd that was crossbred increased from 0.4 for cows born in 1990 to 0.7 in 2000 and 1.6 in 2005. Since 2000, the proportion of genes from Brown Swiss, Jersey, Milking Shorthorn, and nontraditional US dairy breeds has increased, while the proportion from Ayrshire, Guernsey, and Holstein breeds decreased. For cows born in 2005, genetic composition was 0.4% Ayrshire, 1.0% Brown Swiss, 0.4% Guernsey, 90.8% Holstein, 6.5% Jersey, 0.2% Milking Shorthorn, 0.1% other breeds, and 0.7% unknown. Corresponding composition for crossbreds was 2.4, 9.2, 1.1, 44.0, 25.9, 9.3, 1.4, and 6.7%. The most frequent sire breed for crossbreds was Holstein until birth year 1999 and Jersey since then. Frequency of sire breeds for crossbreds born in 2005 was 42% Jersey, 27% Holstein, 13% each for Brown Swiss and Milking Shorthorn, and 5% for all other breeds. About 95% of all first-generation crossbred cows were mated to bulls of one of the crossbred’s parental breeds, most frequently the sire breed. Tracing an animal’s genetic background rather than relying on its coded breed provides a more complete and accurate representation of the extent of crossbreeding and changes in the genetic composition of the national dairy herd.