A comparison of four methods of variance component estimation for heritability of embryonic mortality in turkeys.

A comparison of four methods for variance component estimation to compute heritability of embryonic mortality in the early (Days 1 to 10) and late (Days 21 to 28) incubation period, was performed using Henderson's Method 3, maximum likelihood (ML), restricted maximum likelihood (REML), and minimum variance quadratic unbiased estimator (MIVQUE). Incubation records from Wrolstad Medium White turkeys divergently selected for semen ejaculate volume were the source of data for the present study. Negative sire components of variance were obtained for early mortality by both Henderson's Method 3 and the MIVQUE procedure. Estimates of the sire variance component for the late mortality period were lower (P less than .05) for ML than those obtained using Henderson's Method 3, REML, and MIVQUE. It was concluded that likelihood procedures (ML and REML) are superior for estimating variance components and genetic parameters from unbalanced data.