Zinc content in cow milk and its correlation with amino acid composition

Abstract

Zinc (Zn) is one of the essential elements for all life forms on Earth. Investigation of zinc levels in milk is a topical issue for dairy farming and processing industry. The dynamics of zinc content in milk of cows during 6 months is presented. Milk was obtained from Black-and-White cows at the age of 3–4 years (2–3rd lactation). The strength and direction of correlations with the amino acid composition of milk were established. 132 milk samples from a breeding farm (Krasnodar Territory) were studied in this work. A random sample of 22 lactating cows was drawn from the dairy herd from January through July 2022 (excluding April). Atomic-adsorption analysis with electrothermal atomization, deuterium and Zeeman correction were used in order to accurately determine the level of zinc in milk. Correlations between amino acids and zinc in cow milk samples (in winter-spring-summer period) were obtained, as well as correlation coefficients (r) and coefficients of determination (r2) at certain levels of significance. The zinc content of milk varies greatly from month to month. Insignificant differences relative to January were established in May (higher by 1.54%), June (higher by 9.72%) and July (lower by 7.66%). Significant reliable differences were found in February – higher by 58.15% (p ˂ 0.001) – and in March – higher by 97.34% (p ˂ 0.001) relative to January. All obtained correlations of zinc with amino acids in milk are positive, e.g. for threonine in January r = 0.50 (r2 = 0.25, p = 0.02), in February r = 0.82 (r2 = 0.67, p ˂ 0.01), in March r = 0.25 (r2 = 0.06, p = 0.04), in May r = 0.35 (r2 = 0.12, p ˂ 0.01).