QUALITY INDICATORS OF COW MILK UNDER CHRONIC HEAT STRESS

Abstract

Heat stress during the maintenance of dairy cows, especially chronic, can change the metabolism of lipids in the body, as well as affect the intensity of their oxidation. This experiment was conducted to investigate the effect of heat stress on the milk productivity of dairy cows of the Ukrainian Black and White breed, to determine changes in the fatty acid composition and other quality indicators of the obtained milk. Physicochemical indicators of raw milk were determined by ultrasonic method on the Ekomilk device. To determine the fatty acid composition, methylation of fat obtained from milk was carried out by the Folch method. Identification and quantitative determination of fatty acids was carried out using a flame ionization detector using the gas chromatography method. Dairy processing enterprises can use the temperature and humidity index (THI) indicators of the agro-ecological zone to predict the supply of raw milk and its nutritional value. As the THI index increased from moderate (72 < THI ≤ 80) to severe (80 < THI ≤ 85), the daily milk yield on the farm decreased by 90 kg, an average of 0.459 kg per cow per day, i.e. 0.038 kg per unit of THI index. For each day of severe heat stress on the body of a lactating cow, the total yield on the herd decreased by an additional 24.28 kg of milk (an average of 0.124 kg per cow per day). The restoration of the level of milk supply from the farm can be predicted 7-10 days after the disappearance of symptoms of chronic severe heat stress. Raw milk from cows in a state of heat stress may contain less fat and protein, the density of the secretion may increase slightly. 17 fatty acids were found in the milk of cows. The fatty acid composition of milk shows a relatively high sensitivity to the intensity of the heat load on the body of a lactating cow. This especially concerns a dose-dependent decrease in the level of saturated short-chain fatty acids (C4:0-C6:0). At the same time, an increase in the level of saturated fatty acids C12:0 and C18:0 was noted, as well as an increase in the intensity of secretion by the mammary gland of the polyunsaturated fatty acid C18:2n6c.