Genetic Analysis of Dystocia and Calf Mortality in Israeli-Holsteins by Threshold and Linear Models

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Abstract
Calvings of 106,751 Israeli Holstein heifers were analyzed for dystocia and calf mortality, scored dichotomously, and a composite trait, scored trichotomously. Dystocia was also studied with 146,973 second and third parity records. Models fitted included herd-year-season, sex of calf, calving age, claving month, sire of cow and of calf. Herd-year-season, sire of cow and cald, and residuals were random with diagonal variance-covariance matrices. Herd-year-season variance was assumed to be 10% of the residual component. Other variance components were estimated by REML for linear models and by the conterpart of RELM for threshold models. Heritability estimates were two to five times greater in threshold than in linear models, but correlations between corresponding sire evaluations were all >.9. Linear model sire evaluations were skewed positively, whereas threshold model evaluations had symmetrical distributions. Heritability for dystocia was greater in first than in later parities. Correlations between first and later parity siere evaluations were <.5. Thus, the genetic control of dystocia seems to be different for heifers and cows. Correlations between sire of cow and calf evaluations were <.3. Correlations between dystocia and calf mortality evaluations were about .7.