A study was made of the variation in herd milk composition and the interrelationship of various milk components as factors to be considered in milk pricing schemes, involving milkfat and/or other milk components. As measured by the coefficient of variability, fat was found to be the most variable component, followed by, in descending order of variability, protein, total solids, lactose, and solids-not-fat (SNF). Non-protein-nitrogen (NPN) level averaged 4.36 % of total nitrogen in 99 herd samples collected and analyzed in November, 1978. Coefficient of variation of NPN was 15.18. Thus NPN represents a significant factor in protein analysis where the Kjeldahl procedure is used as a reference standard. This fact lends weight to the desirability of basing milk purchase, if protein is involved, on “true” protein (total nitrogen minus non-protein-nitrogen) rather than total nitrogen.

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Author notes

1Paper No. 11,228, Scientific Journal Series. Minnesota Agricultural Experiment Station. St. Paul, MN 55108.

2INRA, Station Experimentale Laitiere, 39800 Poligny, France.

3Department of Food Science and Nutrition, University of Minnesota, 1354 Eckles Avenue, St. Paul, MN 55108.

4Dairy Quality Control Institute, Inc., 2353 Rice Street, St. Paul, MN 55113.