Heavy metals, nitrates and radionuclides in milk of cows depending on their stress resistance

Abstract

The paper presents the results of studies on the content of cesium, strontium, zinc, cadmium, copper, lead and nitrates in the milk of Ukrainian black-and-white milk breed cows with different resistance to stress. The resistance of cows to stress was determined by concentration of cortisol in the blood one hour after a stress effect. The following factors were stressful: fixation of animals for one hour and pre-selection of blood by a veterinarian for general analysis. The objective of the research was establishing a connection between the different adaptive potential of Ukrainian black-and-white milk breeds and the ability of their bodies to excrete via the milk heavy metal salts, nitrates and radioactive elements which enter the body with food and water. The scientific hypothesis was that the state of pressure which occurs in the body under the influence of stress impairs homeostasis. It can affect the quantity and quality of products, it can cause disorders in the metabolic processes, the synthesis of milk components and introduction of some harmful substances into milk, which are differently accumulated in the body of cows with diverse reactions to stress and can be excreted with milk in at different levels. We established that different resistance of cows to stress can affect the concentration of the investigated harmful substances in milk. Concentration of lead, cadmium, zinc and nitrates was lower in milk of more stress-resistant cows (the first group). Their milk had a lower specific activity of 137Cs and 90Sr. For all the seasons, the reliable results were obtained only for nitrates, and 137Cs and 90Sr – in spring, summer and autumn. Thus, milk of cows with higher resistance to stress is safer in terms of contents of the investigated elements. We have drawn a conclusion that stress can affect the ability of the body to excrete via the milk harmful elements which enter the body with food and water. Perspectives of further research are determining the effect of cows’ stress resistance on the suitability of milk for the production of baby food products.