Influences of Dam on Calving Difficulty and Early Calf Mortality

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Abstract
Influence of dam on calving difficulty and calf mortality was evaluated for repeatability of past performance and daughter-dam relationships. Repeatability for calving performance at first with 2nd parity was 0.16 and for consecutive calvings at 2nd and later parites 0.10. Repeatability for calf mortality from 1st to 2nd parity was 0.02 and for consecutive calving at 2nd and later parities 0.02. A small but renal tendency existed to repeated prior calving performance but not calf livability. Repeatabilities for dystocia were approximately double heritability. Difficulty scores should not be combined because of loss of predictive value of future performance. Relationship of calving difficulty to calf mortality varied depending on whether the calf was born dead or died within 48 h postpartum. Livability scores for those classes should not be combined when calf mortality-calving difficulty interactions are investigated. The hypothesis of negative direct maternal correlation for dystocia resulting from small calves born with ease becoming small cows that have increased dystocia was not disproven for 1st and 2nd parities. Cows with above average difficulty produced daughters with above average difficulty, and heritability of dystocia as a trait of the dam was 0.24 by regression of daughter on dam.