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Selection of Samples Used to Derive the Prediction Equation for Estimating Protein Content by Orange-G Dye-Binding Procedures¹

Department of Animal Industry and Veterinary Science, West Virginia University, Morgantown

ABSTRACT

Protein determinations from Orange-G dye by two spectrophotometers (Bausch and Lomb Type 33-29-40, Beckman Model DB) and nitrogen by micro-Kjeldahl were available on 1,378 monthly test-day samples of milk. These samples were collected for 20 months. The objective was to determine the best procedure for obtaining samples to estimate prediction equations for each month when micro-Kjeldahl determinations are not available on all milk samples. One sampling procedure involved the selection of six samples for each month completely at random, while the other involved dividing the data into high, middle, and low thirds according to their dye-binding readings and selecting two observations from each third for each month.

Considerable variability was present in the magnitude of the correlations between the Kjeldahl and dye-binding estimates of per cent protein by both systems of sampling, indicating that six observations for each month were not sufficient to establish the monthly prediction equations.

¹ Published with the approval of the Director of the West Virginia Agricultural Experiment Station as Scientific Paper no. 921. Supported in part by regional research fund.

² Chemistry Department, Wisconsin State University, Eau Claire.