Genetics of casein content in Brown Swiss and Italian Holstein dairy cattle breeds

Over 2,000,000 records of casein contents were collected from herds of Brown Swiss (BS) and Italian Holstein Friesian (HF) dairy cows in northern Italy during routine milk recording. Variance components for casein and genetic correlations of casein with production and type traits considered in selection were estimated from a sample of 200,484 test day records for 26,279 BS cows and 376,652 for 41,543 HF cows. A multivariate multi-model REML estimation of variance components was made. Models for production included the fixed effects for herd-test day, year of evaluation, days in milk, month of calving and age at calving within parity. Models for type traits were defined accordingly to the model officially used for each breed for breeding value estimation. Breeding values for casein yield and content were calculated from estimated heritabilities (Brown 0.12; Holstein 0.09). Estimates were similar for protein and casein yield and content while genetic correlations with traits in the actual selection indexes differed between breeds. These differences, together with the greater emphasis now given to protein in the selection index of the Brown Swiss than in the Italian Holstein Friesian, suggest that a direct selection for casein could be more advantageous in Brown than in Holstein cows. The Brown breeders association could soon include casein yield and content directly in their selection criteria while that of Holstein cows would wait for a longer term casein data collection.