The genetic relationship between calving interval, body condition score and linear type and management traits in registered Holsteins

The trend to poorer fertility in dairy cattle with rising genetic merit for production over the last decade suggests that breeding goals need to be br oadened to include fertility. This requires reliable estimates of genetic ( co)variances for fertility and other traits of economic importance. In the United Kingdom at present, reliable information on calving dates and hence calving intervals are available for most dairy cows. Data in this study con sisted of 44,672 records from first lactation heifers on condition score, l inear type score, and management traits in addition to 19,042 calving inter val records. Animal model REML was used to estimate (co)variance components . Genetic correlations of body condition score (BCS) and angularity with ca lving interval were -0.49 and 0.47, respectively, thus cows that are thinne r and more angular have longer calving intervals. Genetic correlations betw een calving interval and milk, fat, and protein yields were between 0.56 an d 0.61. Records of phenotypic calving interval were regressed on sire breed ing values for BCS estimated from records taken at different months of lact ation and breeding values for BCS change. Genetic correlations inferred fro m these regressions showed that BCS recorded 1 mo after calving had the lar gest genetic correlation with calving interval in first lactation cows. It may be possible to combine information on calving interval, BCS, and angula rity into an index to predict genetic merit for fertility.