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.
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