Protein profile of cow milk from multibreed herds and its relationship with milk coagulation properties

The aims of this study were to estimate the effect of cow breed on milk protein profile, and to assess the relationship between protein profile and milk coagulation properties (MCP) predicted with mid-infrared spectroscopy (MIRS). The dataset included 173,841 test-day observations of 12,533 specialised (Holstein-Friesian [HF] and Brown Swiss [BS]) and dual-purpose cows (Simmental [SI] and Alpine Grey) sampled in 488 multi-breed herds. Fixed effects considered in the mixed model were breed, month of sampling, parity class, stage of lactation, and first-order interactions and random effects were cow nested within breed, herd and the residual. BS had the greatest casein (CN) fractions content and SI the greatest whey fractions content. A lesser clear pattern was observed when considering the proportion of protein fractions. Longer rennet coagulation, longer curd-firming time and firmer curd were observed for Alpine Grey, HF and BS, respectively. Regarding the index of milk aptitude to coagulate (IAC), BS and SI had the greatest value and HF and Alpine Grey (AG) the lowest one. Weak relationships were estimated between protein fractions and MCP. For whey proteins, all the analysed traits were optimised at β-lactoglobulin (β-LG) concentrations next to the maximum of the physiological range and at α-lactalbumin (α-LA) concentrations at the minimum level. For CNs, all the analysed traits were optimised at α-CN and β-CN concentrations closer to the minimum level and at κ-CN concentration at intermediate levels. Results highlighted the lower efficiency of HF milk for cheese manufacturing compared to the other breeds.Highlights Breed, month of sampling, parity order, stage of lactation and their interactions were important to explain the variability of milk protein fractions and coagulation traits. Brown Swiss (BS) had the greatest casein (CN) fractions content and Simmental (SI) the greatest whey fractions content. Longer rennet coagulation was observed for Alpine Grey, whereas firmer curd was observed for BS. Coagulation properties were optimised in milk with low concentration of α-CN and β-CN and for intermediate levels of κ-casein.