Genetic correlations among body condition score, somatic cell score, milk production, fertility and conformation traits in dairy cows

Genetic and phenotypic parameters for body condition score (BCS), days to first service (DFS), non-return rate (NRR), somatic cell score (SCS), and 305-day milk, fat and protein yields were estimated, using 38930 multiple lactation records of cows across 1830 herds. The cows were daughters of 243 different sires. Singleand multi-trait repeatability animal models were used to estimate parameters based on restricted maximum likelihood methodology. Fixed effects in the model varied depending on the individual trait. Further, genetic relationships between 27 (linear and descriptive) type traits and functional traits (fertility and SCS) were estimated by regressing daughter type records on their sire’s estimated breeding values for functional traits, using the same data set. Estimated regression coefficients were then subsequently used to derive approximate genetic correlations between type and functional traits (DFS, NRR and SCS). Body condition score had a moderate heritability (h2) of 0·26 and fertility traits had a low h2 (0·12 for DFS and 0·06 for NRR). Heritability of SCS and milk production traits was 0·14 and around 0·30, respectively. Ratio of permanent environmental variance to phenotypic variance was higher than h2 for all traits considered and ranged from 0·09 for NRR to 0·45 for milk yield. Body condition score had a favourable genetic correlation (rg) with SCS, but it was not strong (–0·08). Milk production was genetically antagonistic with fertility (rg : range 0·12 to 0·27 with DFS and –0·12 to –0·24 with NRR), with BCS (–0·39 to –0·50), and with SCS (0·10 to 0·15) showing that selecting for milk production alone would lead to decline in genetic merit for these functional traits. Body condition score had favourable genetic correlations with fertility traits (–0·35 with DFS and 0·04 with NRR) suggesting that BCS could be considered in a fertility index. Several type traits (especially ‘udder’ traits) had a favourable genetic relationship with fertility traits and SCS whereas dairy character had an unfavourable genetic relationship. Results of this study on genetic and phenotypic correlations among several functional, type and production traits could be used to design improved selection indexes for dairy producers.