Prediction of Son's Modified Contemporary Comparison from Pedigree Information1,2

Abstract

Son's modified contemporary comparison Predicted Differences and modified contemporary deviations based on daughters’ first lactations only and on all lactations were predicted for milk and fat yield and fat percent from pedigree information. Pedigree records included Predicted Differences and modified contemporary deviations for male relatives and modified contemporary deviations and Cow Index on first available records for female relatives. For a son's dam, however, first two and first three available records also were used. Models were chosen by a stepwise procedure with stopping when there was a change in the multiple correlation coefficient squared of less than 1%. Minimum repeatabilities of 40 and 70% for sons were required also to form two data sets.Models for milk and fat included sire's and maternal grandsire's Predicted Differences and dam's Cow Index. Models for fat also included the modified contemporary deviation for the maternal grandsire. For fat percent, sire's Predicted Difference or modified contemporary deviation and dam's Cow Index were important. Multiple correlation coefficients ranged from .32 for fat percent and .31 for milk to .24 for fat. Two-variable models suggested that for milk and fat, maternal grandsire was more important than dam whereas dam was more important for fat percent. The dam's Cow Index on first available record was more important for milk and fat, but dam's Cow Index from first three available records was most important for fat percent. Results were similar for predicting son's modified contemporary deviations. Closer prediction of son's Predicted Differences to real Predicted Differences for yield of milk and fat could be accomplished by placing slightly more emphasis on the maternal grandsire, and for fat percent, by putting more emphasis on dam's later records.