The control of short-term feed intake by metabolic oxidation in late-pregnant and early lactating dairy cows exposed to high ambient temperatures

•Feeding behavior differed in pre- and postpartum cows exposed to heat-stress.•Heat stressed cows in early lactation had slower postprandial fat oxidation.•Heat stress in early lactation delayed postprandial RQ increase.•Heat stress prolonged feed digestion and shifted fat to glucose utilization.

The objective of the present study was to integrate the dynamics of feed intake and metabolic oxidation in late pregnant and early lactating Holstein cows under heat stress conditions. On day 21 before parturition and again on day 20 after parturition, seven Holstein cows were kept for 7 days at thermoneutral (TN) conditions (15 °C; temperature–humidity-index (THI) = 60) followed by a 7 day heat stress (HS) period at 28 °C (THI = 76). On the last day of each temperature condition, gas exchange, feed intake and water intake were recorded every 6 min in a respiration chamber. Pre- and post-partum cows responded to HS by decreasing feed intake. The reduction in feed intake in pre-partum cows was achieved through decreased meal size, meal duration, eating rate and daily eating time with no change in meal frequency, while post-partum cows kept under HS conditions showed variable responses in feeding behavior. In both pre- and post-partum cows exposed to heat stress, daily and resting metabolic heat production decreased while the periprandial respiratory quotient (RQ) increased. The prolonged time between meal and the postprandial minimum in fat oxidation and the postprandial RQ maximum, respectively, revealed that HS as compared to TN early-lactating cows have slower postprandial fat oxidation, longer feed digestion, and thereby showing a shift from fat to glucose utilization.