Eleven US and 11 Danish young bulls were AI sampled in the US and Denmark. The milking daughters of these sires provided an opportunity for comparison of the US and Danish Jersey populations. Danish age and month of calving and DIM adjustment factors were developed so that Danish and US records could be compared on a standardized basis (305-d lactation, mature equivalent). Least squares and animal model analyses were used to estimate strain differences and effects of heterosis. Jerseys from the US had superiority over Danish Jerseys of approximately 1000 kg for milk and 17 kg for protein. However, Danish Jerseys had an advantage of 20 kg for fat. Estimates of heterosis from crosses of US and Danish Jerseys were 1.5 to 3% of the mean for milk, fat, and protein yields. Correlations of EBV from official genetic evaluations of the US and Denmark were high, ≥78, for the project bulls, providing little evidence of an interaction of genotype and environment.
- yield traits