Bases and Experiences of Expressing the Protein Content of Milk—France

In the early 1960s, France started to analyze routinely protein for the DHIA program using the amido black method, and, since 1969, milk producers have been paid on the basis of fat and protein. Progressively, infrared analyzers have replaced the dye binding method. Because of the rather large variability of NPN content and its role on the accuracy of both amido black and infrared methods, analysis in 1974 was changed from CP to true protein for both economical (NPN has little value) and analytical reasons (better accuracy and centralized calibration). Examples are given to illustrate the seasonal and between-herd variability of the proportion of NPN in total N for which urea is the most important and variable NPN compound. Since 1976, the fat:protein price ratio of additional grams to the basic price changed from 74:26 to 34:66. Several studies have shown that the calibration of infrared instruments in true protein instead of CP provides better accuracy in protein testing with a high correlation (r = –.80) between errors and the percentage of NPN in total N. However, a recent study has shown than urea interferes significantly with the infrared signal. Because protein now has a much higher value than fat, a better definition of protein is extremely important for the dairy industry. After 15 yr of experience, both dairy industry and farmers are quite satisfied, however, using a different reference, yet the problem of the comparison of protein results between France and the other countries remains, especially for breeding programs.