EVALUATION OF EASE OF CALVING FOR CHAROLAIS SIRES

Abstract

A total of 3,221 calving records from four sections of the Charolais Conception-to-Consumer progeny test program (1969–1972 calvings), representing 104 Charolais sires tested in 43 herds, were analyzed to study (1) the effects of different definitions of ease of calving on estimates of variance components and sire proofs, and (2) the effectiveness of evaluating sires for ease of calving by percentage of natural births. Mixed model methods were used on a linear model which considered the effects of section of test, herd, sire, breed of dam, sex of calf and age of dam. Components of variance estimates and sire-predicted differences were computed by iteration. Two definitions which combined ease of calving and calf liveability codes had smaller sire variances and larger error to sire variance ratios than a third definition involving only ease of calving scores. Sire proofs changed with definitions of ease of calving. Rank correlation coefficients between sire proofs from percentage of natural births and predicted differences ranged from 0.5 to 0.8 for the four sections. This suggests that more refined procedures to rank sires should be used.