Effect of Supplementing Diets with Fat on Infrared Analysis of Milk Fat

Abstract

Individual a.m. and p.m. milk samples (n = 1340) were collected in two feeding trials to investigate the effects of amount and source of dietary fat on the determination of milk fat by different analytical methods. Percentage of milk fat was determined by the modified Babcock procedure and infrared instrumentation using either the A filter (5.73 um) or a combination of the A and B (3.48 um) filters. In Trial 1, 24 cows were fed either 0 or .45 kg/d of calcium soap. Mean percentages of milk fat measured by the Babcock, A, and AB methods were, respectively: control, 3.88, 3.88, 3.88; calcium soap, 3.92, 3.93, 3.93. Differences among methods were not significant for either the control or fat-supplemented treatments. In Trial 2, 20 cows were fed 0 or .63 kg/d of either tallow or yellow grease. Milk fat percentages were, respectively: control, 3.43, 3.44, 3.43; tallow, 3.59, 3.61, 3.56; yellow grease, 3.36, 3.36, 3.33. Percentage of milk fat was not affected by analytical method for the three diets. Using data from Trial 1, week of lactation had a greater effect on mean molecular weight of fatty acids in milk than did the feeding of fat. Additional research is warranted to analyze fat in milk from cows under more widely differing dietary conditions. © 1989, American Dairy Science Association. All rights reserved.