Estimated breeding values of differential somatic cell count in Italian Holsteins

Recently, we investigated the genetic aspects of milk differential somatic cell count (DSCC), a novel indicator of udder health that corresponds to the sum of the percentages of neutrophils and lymphocytes in the total somatic cell count (SCC). Information about the proportion of the different cell types in milk, in combination with the overall SCC, would be a valuable asset to better define the udder health status. Our findings served as a prelude for the potential inclusion of DSCC in breeding programmes aimed to enhance cow resistance to mastitis. In the present study, we reported estimated breeding values (EBV) for DSCC and Traditional Somatic Cell Score (SCS) in Italian Holsteins. Variance components used for breeding value estimation were obtained using a model that accounted for the fixed effects of herd-test-day, stage of lactation and parity, and for the random effects of additive genetic animal, permanent environment and residual. In general, we observed the genetic improvement of milk SCS and DSCC across the year of birth of the sires. Correlation between EBV for DSCC and SCS was calculated, and results suggest that a combination of both traits will help identify animals with the genetic potential for lower DSCC and SCC, i.e. bulls with greater genetic merit for mastitis resistance. In particular, 4 groups of bulls could be distinguished: ‘healthy’ (with EBV for both DSCC and SCS <0), ‘susceptible’ (with EBV for DSCC >0 and EBV for SCS <0), ‘chronic’ (with EBV for DSCC <0 and EBV for SCS >0) and ‘mastitic’ (with EBV for both DSCC and SCS >0). Mean EBV for DSCC and SCS by groups of bulls were analysed. Further research is needed to assess the proper weight DSCC should receive in a breeding programme aimed to enhance cow resistance to mastitis.