Collaborative Study to Determine Effects of Milk Composition on Somatic Cell Counts

Quarter, composite, and bulk tank milk samples were analyzed in a three laboratory collaborative study to determine the relationship of milk fat and protein content with milk somatic cell counts. Milk somatic cell counts were determined by two Coulter counters, a Fossomatic counter, and by direct microscopic somatic cell counting. In general, variability among somatic cell counts measured by different procedures was not related to protein or fat content of milk. The greatest percentage of variation between counts that could be explained by fat content of milk was 20.2% between a Coulter and direct microscopic somatic cell counts. The greatest percentage of variation between counts that could be explained by protein content of samples was 12.9% between a Coulter and Fossomatic counts. Breed of cow from which samples were collected also had little influence on differences among milk somatic cell counts. Differences among milk somatic cell counts due to counting methods did vary among quarter, composite, and bulk tank milk samples.