Changes in Fat and Protein Concentrations in Farms with High Milk Production

¹ Ecole Nationale d'Ingénieurs des Travaux Agricoles, Marmilhat, 63370 Lempdes, France

Seventy-six dairy farms composed of high producing (6200 to 8800 kg/yr) Montbéliarde cows that were fed hay-based rations were included in a detailed survey involving the herd and the farm structure, quality of forage, winter and summer feeding practices, and genetic characteristics (breeding value and herd effect for milk production, fat concentration, and protein concentration). These data permitted analysis of the variations of milk composition among farms. The mean annual fat and protein concentrations varied greatly among farms in spite of the homogeneity of the farm sample with regard to milk produced, breed, and type of winter roughage. Such variability results essentially from environmental factors. When farms were classified according to their level of herd effect (fat or protein concentrations), 1) protein concentration variations were greater in winter and linked to different feed characteristics (hay quality, type of concentrate), and 2) variations in fat concentration among farm groups were as marked, if not more so, in summer than in winter. These variations are only partly linked to feeding practices that are beneficial or detrimental to fat concentration (presence of sugar beet in the ration, concentrate distribution method). No correlation occurred between fat and protein herd effects. Therefore, these two variables may be controlled independently by manipulating environmental factors (especially feeding factors).

Key Words: dairy cows • milk composition

Submitted on August 3, 1992
Accepted on November 2, 1992