Cow’s milk has the highest share of total milk production and consumption in the world, including Poland. Milk is the most important source of readily available minerals, particularly calcium, in the human diet. The chemical composition of milk varies depending on genetic, environmental and physiological factors. Changes in the composition and physicochemical properties of milk affect its biological value and processing suitability. The objective of this study was to determine the effect of age of high-yielding Polish Holstein-Friesian (PHF) cows and lactation day on the calcium (Ca) and magnesium (Mg) content of milk. The average milk yield increased significantly during three consecutive lactations. The age of cows had a significant effect on the average Ca and Mg content of milk throughout lactation. Milk from younger cows had higher concentrations of the analyzed macronutrients. The concentrations of Ca and Mg in milk varied considerably depending on the stage of lactation. A substantial decrease in the milk Ca content was noted in the first stage of lactation. The calcium concentration in milk stabilized in the second month post partum, and it remained stable until the end of lactation. A decrease in the Mg content was noted until day 30 of lactation in milk from primiparous cows and cows in their second lactation. The oldest cows produced milk with the lowest Mg concentration, which resulted from a steady decrease in the milk Mg content until the fourth month of lactation. The Mg content of milk continued to increase from the fourth month until the end of lactation, regardless of a cow’s age. The Ca and Mg content of milk from the analyzed high-yielding cows was below the normal ranges (by approximately 24% and 6%, respectively). This is the reason why dairy products are often fortified with minerals.

22.3.2017