Effects of Several Factors on Quantification of Fat, Protein, and Somatic Cells in Milk

Two studies were conducted to determine sources of variation in analysis of milk samples subjected to combinations of handling procedures typical of the Alabama DHIA testing program compared with those of a local milk processing plant. In study 1, cooled bulk tank samples from Jersey and Holstein herds were split and sent to five DHIA laboratories and one milk plant laboratory. All five DHIA laboratories reported similar results for fat with slight differences in percentage protein and SCC. Addition of preservative, shipping on ice, or method of shipping did not affect percentage fat. Milk plant electronic analysis was approximately .05% higher than DHIA. Because the statistical difference is less than the accuracy of the Babcock test ( .1%), the practical significance of the difference is minimal. Samples without preservative or shipped on ice had a higher percentage of protein and lower SCC. Holding preserved samples up to 96 h did not affect eleclronic analysis of percentage fat but resulted in increased percentage protein.