Genetic and genomic evaluation of milk coagulation properties in Italian Holsteins using a reference population of bulls and cows

In Italy, similar to 77% of milk is used for cheese production, with 55% allocated to certified Protected Designation of Origin/Protected Geographical Indication cheeses, making milk cheesemaking ability a crucial factor in the dairy industry. Milk coagulation properties (MCP)-rennet coagulation time (RCT), curd firmness after 30 min (a(30)), and curd firming time (k(20))-are pivotal for assessing milk's suitability for cheesemaking. The present study established a genetic and genomic evaluation system for MCP traits in Italian Holstein cattle. Over 4 million records from 546,944 animals were analyzed using a multiple-trait repeatability animal model. Variance components were estimated via Gibbs sampling, providing heritabilities of 0.33 for casein percentage, 0.11 for RCT, 0.16 for a(30), and 0.15 for k(20). Strong genetic correlations among MCP traits were observed, including -0.87 between RCT and a(30), highlighting their interdependence. Genomic evaluations, incorporating a mixed reference population of bulls and cows, significantly increased the reliability of genomic predictions by an average of 69% for MCP traits compared with using a bulls-only reference population. These findings demonstrate the potential for improving novel traits with moderate h(2), as MCP traits, through genomic selection and underscore the benefits of integrating females into reference populations to enhance the accuracy of genetic evaluations. This approach offers a robust pathway for enhancing milk quality and optimizing cheesemaking processes.