Evaluations for final score at different ages

The objective of this study was to investigate genetic evaluations for final score (PTAT) at different ages. Breeding values were predicted with a random regression model (RRM) and with the current national genetic evaluation model (NE), a repeatability model. RRM included fixed effects for management group and stage of lactation; fixed regressions on age at classification; additive genetic and permanent environmental effects with random regressions on age; and random residual effects. Correlations between PTATs from RRM at various ages and NE ranged from 0.89 to 0.99. PTAT genetic trends for sires and registered cows from RRM at 24 and 60 months of age were similar to those obtained from NE. Trend for grade cows from RRM was lower at 60 month of age than NE trend. The correlation between PTAT of sires and the average age of daughters tended to be positive indicating that daughters of high type bulls are scored more often. Bulls whose genetic evaluation improves as the age of daughters increases tend to have higher genetic evaluations for traits associated with increased longevity. For example, sires with the largest positive difference between PTAT at 60 and 24 months of age had an udder composite evaluation that was 2.7 points higher than those with the largest negative difference in PTAT at the two ages. Proportion of registered cows in the data set decreased from over 80% for cows born in 1981 to 55% for cows born in 1997. Registered cows have mostly two or more scores while grade cows tend to have only a single score at an early age. Declining numbers of scores at later ages may result in selection of sires whose daughters are superior at an early age but age poorly. Evaluation for final score by the random regression model allows identifying bulls whose daughters# are superior at an early age and mature gracefully.