Phenotypic and genetic aspects of milk freezing point in primiparous Holstein Friesian cows

Freezing point (FRP) of milk and its associations with milk traits have not been studied in Italian Holstein Friesian population yet. Moreover, in other countries, studies were based on small sample size. Therefore, the aim of the present paper was to investigate sources of variation of milk FRP, and to estimate its heritability and genetic correlations with milk yield and quality traits. An analysis of variance was carried out to identify sources of variation of FRP, and genetic parameters were assessed using test-day repeatability animal models on 37,331 records from 5,102 first-lactation cows in 435 herds. Only classes of days in milk and herd-test-date significantly affected FRP. Heritability and repeatability of FRP were low (0.12 and 0.23, respectively), and moderate genetic correlations of this trait with lactose percentage (-0.52), protein content (-0.32) and somatic cell score (0.29) were estimated. Despite low, heritability of FRP is comparable to that of other traits such as somatic cell score, suggesting that there is room for applying selection strategies to improve this trait, also exploiting its genetic relationships with other milk traits.