Secondary traits: sire evaluation and the reproductive complex.

Genetic aspects of dystocia, reproduction and its association with production, and calf livability are reviewed. Measures of each are presented. Genetic and maternal effects, sire evaluation by births from heifers and older cows, and correlations with production and type are discussed for dystocia. Heritabilities for measures of reproduction were low. Fertility and production were antagonistic in cows but complementary between heifer breedings and production in first lactation. There were differences among sires for calf mortality up to 48 h after birth, but heritabilities were low. Livability and dystocia are closely correlated genetically. Methods for multiple traits ideally should be used for sire evaluation.