Effect of two simulated heat waves on technological properties of cow milk

International audience

anglais. During summer, dairy cows experienced heat stress, impacting their welfare and health but also their productivity and milk quality. While heat stress impacts milk composition, its effect on technological properties like heat stability and lipolysis remains unclear. These properties can not be corrected at the plant, making farm-level control crucial. This study aimed to evaluate the impact of heat waves on these properties. Six cows were housed in 2 temperature-controlled rooms with ad libitum diet and water. They underwent 1 wk of neutral temperature (19°C), followed by 1 wk of heat stress (36°C by day, 19°C by night), and one-week recovery at 19°C. This sequence was repeated to simulate 2 consecutive heat waves. Heat stability was assessed using ethanol and Ramsdell tests, while lipolysis was measured by infrared spectroscopy, on the last day of the 1st week, and at each milking on the 1st, 2nd, and last day of the 2 following weeks of both repetitions. Milk yield, fat content, and protein content were recorded daily at each milking. A mixed model analyzed separately the variation of these parameters in the morning and evening milkings, considering day, repetition, and room along with their interactions as fixed effects, cow as a random effect, and day within repetition per cow as a repeated measure. Milk yield and protein content decreased during both heat waves but returned to initial levels at the end of recovery period, with a lower amplitude in the 2nd wave for protein content. Fat content increased initially but then return to baseline during heat stress. Ramsdell test showed increased stability during the first 2 days of heat stress, decreasing afterwards and throughout recovery. Ethanol test results showed similar trends during the 1st heat wave but no significant variation during the 2nd one. Lipolysis was higher in the evening milk at the end of the 1st heat wave and for 3 d afterward, with no significant variation during the second. Heat waves affected the technological properties of milk, with some variations between repetitions. Further analysis of milk fine composition is ongoing to explain these technological changes.