Milk of animal origin, characterized by high nutritional value and exceptional flavour, is one of the most popular and valuable components of the human diet. Milk is a rich source of protein, fat, lactose, vitamins and minerals such as calcium, phosphorus, potassium, magnesium, sodium, iodine, chlorine, iron and zinc. The mineral composition of milk may vary widely depending on genetic, physiological and environmental factors. The aim of this study was to determine the effect of milk production performance of Black-and-White Polish Holstein-Friesian (PHF) cows on the concentrations of potassium (K), calcium (Ca), magnesium (Mg), sodium (Na) and zinc (Zn) in milk and its proximate composition. Mineralized milk samples were assayed for the content of K, Ca, Na by atomic emission spectroscopy (AES), while Mg and Zn were determined by atomic absorption spectrometry (AAS). The production performance of the evaluated PHF cows was high, at 11028 kg of milk over 305-day lactation on average. Milk yield had a significant influence on the average content of lactose, K and Na in milk during the 305-day lactation period. The concentrations of Ca, Mg and Na in the analyzed milk samples were below the lower reference limits, whereas the levels of K and Zn were high. The K and Na content of milk varied considerably across lactation stages. In early lactation, K levels were particularly high in cows producing up to 10 000 kg of milk. The Na content of milk increased steadily from the fourth month until the end of lactation. Cow productivity was negatively correlated with the concentrations of lactose, K and Ca in milk. Highly significant positive correlations were found between the fat content of milk vs. the levels of Ca, Mg and Zn. The results of this study indicate that milk from high-producing cows may have insufficient concentrations of selected minerals, relative to the relevant standards.

23.2.2018