2008 Annual Report 1a.Objectives (from AD-416) 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. 1b.Approach (from AD-416) 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. 3.Progress Report Because previous work demonstrated a strong relationship between herd heritability and sire misidentification rate, current work has focused on identifying specific cows with a likely misidentified sire based on deviations of yield, somatic cell scores, and milk components from expected values. A preliminary investigation of the association between residual model effect for cow's milk yield and simulated sire misidentifications was conducted, and a significant relationship was found. A scientific paper on the relationship between individual-herd heritability and sire misidentification and a scientific short communication on the relationship between individual-herd heritability and estimates of genetic parameters were accepted and published by the Journal of Dairy Science. The project deadline was extended from June 30, 2008, to June 14, 2009, to allow the Cooperator to explore implementation of the research results fully. Monitoring activities for the project included phone and e-mail exchanges between Animal Improvement Programs Laboratory and Cooperator scientists, discussion at one scientific meeting, and one trip by the ARS scientist to the Cooperator's site for collaboration.