The aim of this study was to gain a better understanding of the relationship between calcium status and physicochemical properties, and of milk stability when subjected to various processing treatments. Variations in milk due to breed, stage of lactation. season and diet (spring flush) were studied. When comparing Friesian and Jersey cows milk, Jersey cows milk contained more protein, fat and calcium but less ionic calcium. Correlations exist between the protein and calcium concentration, which affects other characteristics such as stability and clotting properties. Spring flush did not have a statistically significant effect on changes in the data obtained; however, the data did differ statistically significantly from week to week. There was a lot of variability in the samples during the summer months, which could be attributed to heat stress because of particularly hot weather during the summer of 2006.