Classical and Bootstrap Estimates of Heritability of Milk Yield in Zimbabwean Holstein Cows

The h2 of first lactation milk yield in Zimbabwean grade Holstein cows was estimated as the regression of daughter on the dams' adjusted milk yield, using least squares, least absolute value, bootstrap restricted least squares, and bootstrap restricted least absolute value estimators. The estimators were evaluated for efficiency and robustness in estimating h2. The estimated h2 were .272, .265, .283, and .290 by least squares, least absolute value, bootstrap restricted least squares, and bootstrap restricted least absolute value procedures, respectively. The classic 90% confidence intervals for h2 were .030 to .514 by least squares and .056 to .474 by least absolute value procedures. The bootstrap restricted least squares 90% confidence interval for h2 was .000 to .542, and the bootstrap restricted least absolute value 90% confidence interval was .000 to .615. The point estimates by the four procedures were comparable, but the bootstrap confidence intervals were more conservative than their classic counterparts. The least absolute value estimator was the most efficient and the second best in robustness. The least squares estimator was second best in efficiency and worst in robustness. The bootstrap restricted least absolute value estimator was the least efficient and the second best in robustness.