Influence of Feeding Protected Tallow on Accuracy of Analyses by Infrared Milk Analyzer

Abstract

To determine whether feeding cows protected-tallow supplement influences reliability of analyses of milk composition by the infrared method, we measured fat, protein, and lactose in milk produced by three groups of seven Holstein cows fed supplement at 0 (basal), 15% (medium), and 30% (high) of their ration for the first 15 wk postpartum. Samples from individual milkings were collected every 3 wk from cows in each group. Reference methods for the Infrared Milk Analyzer were Babcock test for fat, Udy dye-binding for protein, and a polarimetric method for lactose. Fatty acid composition was determined by gas chromatography. The differences, reference method minus infrared, for cows in the basal, medium, and high groups were: for fat −.01, .29, and .30%; for protein, .08, −.02 and .03%; and for lactose .05, .25, and .21%. For cows in the medium and high groups, differences for fat were correlated with the mean molecular weight of the triglyceride fatty acids. Cows in all three groups were switched over to a common ration for wk 16 to 20, and the sampling schedule was modified so that two samples were collected from each cow at a 2-wk interval. Differences on this ration for cows in the basal, medium, and high groups were: fat −.05, .03, and .01%; for protein .03, .05, and .06%; and for lactose .12, .15, and .10%. Differences for fat and lactose when the cows were fed protected-tallow supplement were attributable largely to feeding the supplement and the resulting change in fatty acid composition of the milk fat. To avoid errors in measuring fat and lactose in milk from cows fed protected-tallow supplement by infrared analysis, the instrument must be calibrated specially.