Differences in heritability estimates from multiple-trait and repeated-records models.

Analyses of ovulation rates in consecutive estrous cycles with multiple-trait and repeated-records animal models resulted in different estimates of heritability. The estimate from the repeated-records model was seen to be approximately the product of the average genetic correlation and the average heritability from the multiple-trait procedure. A simple model is used to show algebraically that such a result is expected, particularly if the environmental correlations are small among records of the same animal. Comparison of results of the two types of analyses of 10 replications of 10 combinations of underlying heritabilities and genetic correlations confirms this explanation.