Characterization of French dairy farm environments from herd-test-day profiles.

Genotype by environment interactions are ignored in national genetic evaluations of dairy cattle. However, some breeders consider that the genetic merit of top sires is not correctly estimated for use in their own particular environment or with their own herd management. With the objective of later investigating genotype by environment interactions at the national level, we studied the relationship between herd management (e.g., feeding system, herd size, production, workforce) and herd-test-day (HTD) profiles for milk yield and contents of fat and protein using a database of 934 herds. Herd-test-day profiles, estimated using a test-day model, are thought to reflect herd management because they represent the part of production due only to month-to-month variations in environmental conditions of production; that is, those related mainly to feeding and climate conditions. Herd clustering based on results from a factor analysis of descriptors of HTD profiles was performed. Each cluster of herds was then characterized in terms of herd management. Three herd clusters were identified. Cluster 1 was characterized by low HTD profiles for milk yield and protein and fat contents as well as a low level of intensification. Cluster 2 was defined by a high milk yield HTD profile and a high level of intensification. Cluster 3 consisted of herds with HTD profiles showing high protein and fat contents but it was difficult to link this cluster to any specific herd management. The use of clusters based on HTD profiles as descriptors of distinct herd management systems will be used in a genotype by environment interaction study in France.