Factors Affecting Differences in Milk Fat Test Obtained by Babcock, Rose-Gottlieb, and Infrared Methods and in Protein Test from Infrared Milk Analysis

In a collaborative study between personnel of the Canadian dairy cattle Record of Performance Services, university laboratory, and central milk testing laboratory of Quebec Dairy Herd Analysis Service, differences in fat tests by Babcock, Rose-Gottlieb, and infrared analyses (Milko-Scan) were studied in individual milk samples from Ayrshire, Holstein, and Jersey herds for 1 yr. On-farm Babcock for fat gave results that were lower by .075, .058, and .016% than laboratory Babcock tests for Ayrshire, Holstein, and Jersey milks. Fat tests by Rose-Gottlieb and Milko-Scan on day of sampling were intermediate between the on-farm and laboratory Babcocks for Ayrshire and Holstein. For Jersey milk, using Rose-Gottlieb as reference method, fat would be overestimated by .021, .037, and .082% when compared with on-farm Babcock, laboratory Babcock, and Milko-Scan results. Lower fat tests were obtained by infrared for 3-d-old samples transported under varying ambient temperature conditions; however, these were not due to error of the instrumental method per se but rather to conditions of milk samples which may have caused the milk to undergo lipolysis. Magnitude of the d 3 fat depression, which varied from nonsignificance to .21%, was accompanied by an increase in protein reading