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Effect of Stage of Lactation on Accuracy of Estimating Milk Protein Using Orange G Dye Binding¹

Department of Dairy Science, Washington State University, Pullman

ABSTRACT

Dye binding is used for estimating the protein in milk of individual cows. Generally, milk is sampled at monthly intervals, beginning as early as the seventh day following calving. In this regard, two questions arise relative to accuracy of estimation of the protein. Can the dye-binding method of Ashworth et al. (1) be used to estimate protein in milk samples early in lactation? Is milking-to-milking variation in protein following calving so erratic that yield of protein during the first test period following calving cannot be reliably estimated? Some of the data of Ashworth et al. (1) were re-examined for possible stage of lactation effects on the accuracy of determining protein using dye binding.

It is known that per cent fat in milk from an individual milking of a cow may vary considerably throughout lactation (3). This variation is most extreme early in lactation (4). Garrett and Overman (4), summarizing the results of 25 investigators, observed that milk fat varied less (0.15–9.55%) than protein (4.80–27.35%) in colostrum at calving.

¹ Scientific paper No. 2199, Washington Agricultural Experiment Stations, Pullman. Project 1378.

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