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* Animal Improvement Programs Laboratory,
Agricultural Research Service, USDA, Beltsville, MD 20705-2350 Dairy and Swine
Research and Development Centre, Agriculture and Agri-Food Canada, Sherbrooke,
Quebec, Canada, J1M 1Z3 Canadian Dairy Network, Guelph, Ontario, Canada, N1G
T42
Nederlands Rundvee Syndicaat (NRS), Arnhem, the Netherlands
1 Corresponding author: dnorman{at}aipl.arsusda.gov
Differences among bulls in maturity rate of their daughters
for milk yield were investigated. Milk records for US Holsteins
with first-parity calving dates between 1960 and 1998 were used
to calculate 3 evaluations for bulls based on daughter records
from parity 1, parities 1 and 2, and parities 1, 2, and 3. The
3 evaluations were used to estimate parity-specific evaluations
for parities 2 and 3. Maturity rate of Holstein bull daughters
in Canada and the Netherlands was compared with that for daughters
of the same bulls in the United States by using official November
2004 Canadian and August 2005 Dutch parity-specific evaluations.
For bulls with 
500
first-parity daughters, correlations among parity-specific
evaluations within country and birth year of bull were 0.88 between
parities 1 and 2, 0.84 between parities 1 and 3, and 0.96 between
parities 2 and 3 for the United States; 0.90, 0.86, and 0.97,
respectively, for Canada; and 0.92, 0.89, and 0.98, respectively, for
the Netherlands. Correlations between Canada and the United States
for within-country differences between evaluations for parities 1 and
2 were 0.72 for bulls with 50 first-parity daughters and 0.89 for bulls with 500 first-parity daughters;
corresponding correlations between the Netherlands and the United
States were 0.66 and 0.82. Correlations between countries for
differences between evaluations for parities 1 and 3 were slightly
less, and corresponding correlations between evaluations for parities
2 and 3 were still lower. To establish whether differences between
parity-specific evaluations were genetic, comparisons were made
across a generation. Coefficients for regression of son on sire
within country and birth years of sire and son for parity-specific
evaluations and differences between parity-specific evaluations
ranged from 0.35 to 0.53, with standard errors of 
0.04. Differences in maturity rate
of bull daughters were quite consistent across country, and
those differences were transmitted to the sons’ daughters.
Modeling to account for maturity differences should increase the
accuracy of US evaluations and reduce fluctuation between
evaluations, especially for bulls with daughters that deviate
substantially from the population mean for maturity rate for milk
yield.
Key Words: genetic evaluation • maturity rate • milk yield • parity
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