The study was conducted in a herd of Polish Holstein-Fresian (PHF) cows. Experiments involved primiparous cows. Protein, fat and lactose content as well as dry matter, fat free dry matter, pH, °SH, density and thermostability were determined in milk samples. RW-2 prints served to evaluate the performance of cows. Differences in the properties of milk depending on stage of lactation were analyzed. Milk yield in primiparous cows increased until 90 days of milking and decreased from the fourth month of lactation. The study showed the highest levels of fat, protein, dry matter and fat content in milk from cows in the eleventh month of lactation. In XIII month lactation milk, characterized by the highest dentysity of a pH close to the isoelectric point of casein. We conclude that in the period of lactation performance, composition and physic-chemical characteristics of mammary gland secretions of cows are subject to change, and milk with the most desirable technological properties producing cows in the XI and XIII month milking.

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