Short Communication: Variance estimates among herds stratified by individual herd heritability

Authors: DECHOW, C - PENN STATE UNIV; NORMAN, H; PELENSKY, C - PENN STATE UNIV

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2008
Publication Date: 4/1/2008
Citation: Dechow, C.D., Norman, H.D., Pelensky, C.A. 2008. Short Communication: Variance estimates among herds stratified by individual herd heritability. Journal of Dairy Science. 91(4):1648-1651.

Interpretive Summary: Individual herd heritability estimates can be generated with regression techniques. Records from herds with high, medium, and low individual herd heritability estimates were pooled. As herd heritability estimates increased, genetic variance estimates increased and permanent environmental variance estimates decreased in the pooled samples.

Technical Abstract: The objective of this study was to compare genetic parameter estimates among herds stratified by high, medium and low individual herd heritability estimates. A regression model was applied to milk yield, fat yield, protein yield and somatic cell score (SCS) records from 20,902 herds to generate individual herd heritability estimates. Herds representing the 5th percentile or less (P5), 47th through the 53rd percentile (P50) and the 95th percentile or higher (P95) for herd heritability were randomly selected. Yield or SCS from the selected herds were pooled for each percentile group and treated as separate traits. Records from P5, P50 and P95 were then analyzed with a three-trait animal model. Heritability estimates were 23%, 31%, 26% and 8% higher in P95 than in P5 for milk yield, fat yield, protein yield and SCS, respectively. Regression techniques can be used to stratify individual herds by heritability and additive genetic variance increased progressively and permanent environmental variance decreased progressively as herd heritability increased.