Genetic aspects of milk β-hydroxybutyrate in Italian Holstein cows

The aim of this study was to estimate heritability of milk β-hydroxybutyrate (BHB) and its genetic relationships with milk production and composition traits in early lactation (5 to 100 days in milk) of Italian Holstein cows. The dataset consisted of 67,131 test-day milk analyses from 21,223 cows of different parity. Estimate of heritability for milk BHB was 0.08 ± 0.01. The strongest genetic correlation was observed between BHB and fat-to-protein ratio (0.33 ± 0.07), whereas genetic relationships between milk BHB and other milk traits were weak, ranging from -0.07 ± 0.07 with urea to 0.21 ± 0.06 with fat percentage. Although milk BHB routinely determined in milk samples during early lactation is a lowly heritable trait, genetic improvement can be made through appropriate breeding strategies to reduce the susceptibility of cows to ketosis in Italian Holstein population