Project Number: 1265-31000-096-02
Project Type: Specific Cooperative Agreement

Start Date: Jun 15, 2004
End Date: Jun 14, 2009

Objective:
1) Determine the effectiveness of using within-herd heritability estimates in genetic analyses; 2) Estimate change in genetic parameters for yield and SCC across various herd sizes and herd production levels; and 3) Investigate the use of random regression models to estimate maturity rate and change in production across lactations.

Approach:
The cooperator will obtain milk, fat and protein yield, somatic cell scores, herd average and herd size records from AIPL-USDA. Within-herd heritabilities will be estimated for several randomly selected herds using REML and compared to estimates using less computationally intensive methods, including daughter dam regression and paternal half-sib intra-class correlations. Breeding values will be generated assuming specific within herd heritabilities and compared to breeding values generated assuming a constant heritability across all herds and from random regression models with heritability varying across herd sizes and average yield. Estimated breeding values for specific herd sizes and production levels will be calculated to determine if significant re-ranking of bulls occurs across various herd parameters. Breeding values for maturity rate (or change in production across lactations) will be generated by estimating a level for each sire and a linear change across lactations.