Changes in milk production and fat and protein contents in farms : effects of genetic and environmental factors

Abstract

Sixty three dairy farms with Holstein cows were included in a detailed survey involving the herd and the farm structure, quality of forage (including chemical composition), winter and summer feeding practices, and genetic characteristics (breeding value and herd effect for milk production, fat content and protein content). Body condition of the cows were recorded. These data permitted analysis of the variations of milk production and composition among farms. The mean annual production varied from 5040 to 8330 kg, fat content from 36.5 to 42.9 g/kg and protein content from 28.1 to 32.4 g/kg. Such variability results essentially from environmental factors. The lowest milk and protein content occurred in farms where feeding factors were the least favourable (insufficient roughage energy value for heifers and then for producing cows) and where body condition of the cows the lowest. The absence of correlation between milk production herd effect and protein content herd effect is discussed. In particular, the role of the type of roughage, body condition of the animals and their health is envisaged. Variations in fat content were mainly related to the type of ration (presence or absence of maize silage).