Recently, a significant amount of data has been reported indicating on the link between consumption of dairy products and development of oncological diseases. This could be explained by the presence in milk of various hormones, particularly insulin-like growth factor (IGF). This hormone is a mediator between somatotropin and tissues. In response to the increase of the blood level of growth hormone, hepatocytes begin actively synthesize the IGF, which accelerates the rate of the metabolism,

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... ding those of onco-cells. The majority of studies relate to humane medicine, and data on the dependence of IGF milk levels on breed, period of lactation, diet, physiological, and clinical status of an animal are lacking. Taking this into consideration, the purpose of this study was to analyze the concentration of insulin-like factor in colostrum, milk of cows and blood plasma at various stages of lactation. Study was performed on cows of Ukrainian black-and-white dairy breed in their from second to fifth lactation with milk yield 5100–5700 kg per previous lactation. Concentration of IGF was detected in colostrum, milk and plasma of cows, using enzyme immunoassay. Obtained material gives evidence that the highest IGF level is present in colostrum. After that hormone concentration decreases up to 10–14 day of lactation. High level of IGF in colostrum might be associated with necessity to stimulate metabolism of calves in early postnatal period of ontogenesis. Immediately after calving plasma level of IGF decreases. The highest level was observed on 10–14th days of lactation. Taking into consideration physiological function of the given hormone, there is no univocal explanation of the decrease of its plasma level in cows at the beginning of lactation. This could be associated with energy deficit, physiological condition of animals or with developing of lactation dominant and levels of other hormones. Potential of further research lies in investigation of the dependence of the IGF level in the secretion of the mammary gland on productivity, breed, age and diet of animals.