Genetic relationships between calving interval and linear type traits in
Genetic correlations between first calving interval (CI) and linear type traits in South African Holstein and Jersey cattle were estimated to assess the possibility of using type information as selection criteria for CI. All linear type traits routinely evaluated under the National Genetic Evaluation Programme (18 for Jersey and 17 for Holstein) were considered. Data were obtained from the National Dairy Animal Recording Scheme and comprised records of 30 503 Holstein cows in 640 herds and 27 360 Jersey cows in 460 herds. Multiple-trait animal models were used to estimate parameters, based on the restricted maximum likelihood (REML) methodology. Fixed effects in the model varied depending on the individual trait. Linear type traits reflecting body size generally had much higher correlations with CI than udder characteristics. Genetic correlations of CI with body size traits were mostly positive in both breeds, ranging from 0.04 ± 0.16 with bone structure to 0.51 ± 0.08 with body depth, dairy strength and rear leg set. Correlations between CI and body depth (0.51 ± 0.08), angularity (0.32 ± 0.08) and rump angle (0.32 ± 0.12) indicate that cows with deep, more angular bodies and low pins have longer CI. Genetic correlations with udder type traits were generally low, ranging from -0.01 ± 0.20 with udder width to 0.25 ± 0.11 with rear teat placement. The highest genetic correlations with CI were for rear leg rear view (-0.70 ± 0.34), body depth (0.51 ± 0.08), dairy strength (0.51 ± 0.09), rear leg set (0.51 ± 0.06), foot angle (-0.44 ± 0.04) and rump angle (0.32 ± 0.05) in the Jersey and rump height (0.31 ± 0.08), angularity (0.32 ± 0.08) and body depth in the Holstein (0.51 ± 0.08). These traits may therefore be used in the analysis of CI to carry out early prediction of fertility and increase the accuracy of evaluation.