Genetic and environmental relationship among calving interval, survival, persistency of milk yield and somatic cell count in dairy cattle

Abstract

Data from Australian Holstein–Friesian cattle on calving interval (CI), survival (Surv), mean milk yield (MY), mean fat yield (FY), mean log e somatic cell count (LnSCC) and the regression of MY, FY and LnSCC on days in milk (called persistency for MY and FY and slope for LnSCC) were analysed to estimate heritability (h 2), genetic and environmental correlations using a multi-trait sire model. The dataset consisted of 87,942 and 50,469 cows with milk yield records in the first and second parity, respectively. Among the traits, the highest h 2 (0.32) was estimated for mean MY in the first parity and the lowest (0.02) was for Surv (parity 1 and 2). The h 2 estimates for persistency of MY were 0.09 and 0.11 while those for CI were 0.04 and 0.03 in the first and second parity, respectively. The antagonistic genetic correlation between mean MY and CI increased from 0.43 in the first to 0.58 in the second parity while that of persistency of MY (parity 1 and 2) with CI (0.04 to 0.18) and Surv (−0.06 to 0.18) were close to zero. In general, environmental correlations between traits were lower than genetic correlations. The across parity genetic correlations (e.g. CI in parity 1 with Surv in 2) were similar to the within parity correlations. Fitting day of gestation as a covariate when analysing milk yield reduced the environmental correlation between persistency of MY and CI from 0.16 to near zero. It is suggested that fertility be included in the breeding goal to halt or minimise further deterioration in fertility due to selection for MY. However, selection for persistency of MY may not improve fertility or survival.