Prediction of Sire Effects for Probability of Survival to Fixed Ages with a Logistic Linear Model

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Abstract
A logistic linear model was used to predict sire effects on the underlying continuous scale for observed daughter survival rates to fixed ages. Results were compared with linear model prediction without logistic transformation. Fixed age categories of 41 and 54 mo had 720 and 615 sires with 18,941 and 16,437 sampling daughters. Sire variances were estimated on the underlying continuous scale from a data subset. The logistic linear model accounts for unequal subclass variances due to different mean survival rates in herd-year-seasons. Results with logistic linear model give heritabilities of .28 and .26 for 41 and 54 mo on underlying scale, corresponding to .12 and .15 on phenotypic scale. Genetic trend for daughter survival in sires was found for both fixed ages. Rank correlations between logistic and linear predictions were .61 and .70. Comparing top and bottom 5% of sires in each ranking indicated substantial differences; a few sires differed by 300 ranks out of a possible 615 for 54 mo.