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Influence of Dairy Rations with Whole Cottonseed or Extruded Soybeans on Accuracy of Analyses for Milk Components

Departments of Food Science and Technology and Animal Science, University of California, Davis 95616

ABSTRACT

To determine whether dairy rations influence the accuracy of component analyses, fat, protein, lactose, and total solids were measured in milk produced by Holstein cows fed a basal ration or a ration containing either 7% extruded soybeans, 15% whole cottonseed, or 30% whole cottonseed for the first 15 wk postpartum. Samples from individual milkings were collected in the 14th and 15th wk from 12 or 13 cows in each group. Reference methods were Mojon-nier for fat, Udy dye-binding for protein, polarimetry for lactose, and forced-air oven for total solids. The methods compared to reference methods were Milkotester and Babcock for fat and Infrared Milk Analyzer for fat, protein, lactose, and solids-not-fat. Fatty acid composition was determined by gas chromatography. For cows fed 30% whole cottonseed, Infrared Milk Analyzer fat measurements averaged .14% lower than by Mojonnier. For cows fed extruded soybeans or whole cottonseed, Milkotester fat measurements were higher than by Mojonnier, and Infrared Milk Analyzer protein measurements were higher than by Udy dye-binding. For cows fed whole cottonseed, Infrared Milk Analyzer solids-not-fat measurements were higher than by forced air oven. For cows fed extruded soybeans or whole cottonseed, differences between Babcock and Mojonnier fat measurements and between Infrared Milk Analyzer and polarimetric lactose measurements were not affected. For cows fed whole cottonseed, the mean molecular weight of the fatty aicds of milk fat was increased.