CONCLUSIONS

1. INTRODUCTION Various AIPL reports have provided information on numbers and percentages of breeds for the production-tested US dairy population. This report provides percentages by breed contribution from the full female pedigree file including crossbreds. Previous reports have either ignored crossbreds or assigned them to a single breed whereas this report considers the fractional contributions from the pedigree. OBJECTIVE Determine the composition of US dairy cattle across time, according to breed background. • DATA & METHODS • 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. • Before adjustment to the pedigree file, for cows born in 2005, for example, 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. • Applying a set of rules to assign a breed where none was reported, reduced the percentage of animals born in 2005 having an unknown breed to 1.0% in all females and 30.3% in crossbreds. RESULTS Percentages of population attributed to breeds for females born in 2005 • Holsteins continue as the predominant provider of genes. • Jersey contribution declined from 1990 to 1995, but increased thereafter. • Ayrshire, Brown Swiss, and Guernsey contribution has declined. • Milking Shorthorn contribution has been fairly steady as has the total for remaining breeds while unknown background has increased. Mating sire breed for various F1 crosses Percentages of sire breeds for crossbred females • About 95% of all first-generation crossbred cows were mated to bulls of one of the crossbred’s parental breeds: sire breed 58%, dam breed 37%. • Use of a third breed was relatively infrequent, ranging from 3 to 9% (average of 5%). • Crossbreds represent a different mix of breed background than among purebreds: much less Holstein and more of non-traditional breeds. It is disappointing that so many crossbreds trace to animals with an unknown (actually, unreported) breed. • The percentage of cows in the national database that are crossbred increased from 0.6 for cows born in 1990 to 1.3 in 2000 and 3.0 in 2005. • CONCLUSIONS • The increase in frequency of crossbreds will make it even more useful to identify genetic background to monitor the population rather than relying on the reported or evaluation breed of an animal. • As expected, Holsteins are contributing the most genes, but the impact is less among crossbreds. • Three-way crosses were infrequent. The tendency was to mate F1s to the sire breed, suggesting breed change more than infusion of outside genes for one generation. • Non-traditional breeds are having little impact, even among crossbreds. • These results and interpretations are dependent on the data reported and are impacted by any systemic changes in completeness or accuracy of reporting, including characteristics of the production-tested population. Percentages of genes by breed in females born in different years • The most frequent sire breed for crossbreds was Holstein through birth year 2000 and Jersey since then. • Frequency of Guernsey, Ayrshire, Milking Shorthorn, and non-traditional breed sires generally declined, while Brown Swiss was similar in 1990 and 2005. • Crossbred sires are rare but sires of unknown breed increased markedly in the late 1990’s.