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Estimating Solids-Not-Fat and Protein in Milk from Different Sources Using Percentage Milk Fat, Protein, and Solids-Not-Fat¹

Department of Dairy Science, Washington State University, Pullman

ABSTRACT

The major components of milk were determined to compare the relative accuracy of indirectly estimating protein and solids-not-fat (SNF). The study included 2,842 monthly test-day samples from Guernsey, Holstein, and Jersey cows, 960 semimonthly composited samples from 40 herds, and 718 bulk milk samples from 64 herds representing one two-day composite monthly.

Standard errors of estimate (s_{y · x}) for within breed when using per cent milk fat to estimate per cent SNF were 0.53, 0.25, and 0.17% SNF, respectively, for monthly samples from individual cows, lactation averages, and two-day composites of herd milk; similarly compared, when per cent protein was used to estimate per cent SNF, the s_{y · x} were, respectively, 0.47, 0.19, and 0.14% SNF.

Percentage milk fat and per cent SNF (gravimetrically determined) were compared for indirectly estimating per cent protein. The within breed s_{y · x} for monthly samples from individual cows, lactation averages, and two-day composites of herd milk were, respectively, 0.32, 0.16, and 0.17 for per cent milk fat and 0.29, 0.14, and 0.15 for per cent SNF.

Correlations and regression equations from this study are compared with data of others. More attention should be given to breed, source of milk (cows or herds), length of composite period, and numbers of cows or herds involved when attempting to interpret the extensive literature on this subject.

¹ Scientific Paper No. 2213, Washington Agricultural Experiment Stations, Projects 1183, 1296, and 1542.

² Present address: Department of Animal Sciences, Purdue University, Lafayette, Indiana.

³ Professor Emeritus, Washington State University.