Effect of once daily 5-h or 10-h cold-exposures on body temperature and resting heat production of beef cattle

Abstract

Twelve yearling crossbred beef heifers weighing 454 ± 31 kg were randomly assigned to either 0 h (control), 5 h (5CE; 0800 to 1300) or 10 h (10CE; 0800 to 1800) of cold exposure (-20°C) daily to determine the effect of daily cold exposures of different durations on body core temperature and resting heat production of beef cattle. Treatments were imposed for a 21-d period (seven intervals of 3 d duration) using two replications with two heifers per treatment × replication combination. Heifers were group housed outdoors in a pen with overhead shade at one end and were moved daily at 0800 to a group pen in either a control room or an environmental chamber set at -20°C. After the 21-d period was completed, resting heat production was measured in a thermal neutral environment for 5 h. Vaginal temperature (Tvag) was continuously monitored using radiotransmitters. Treatment did not affect daily maximum, mean or minimum Tvag, the amount of time spent at Tvag exceeding daily mean Tvag, or the variability of Tvag (P ≥ 0.29). However, when examined within specific phases of the day, treatment effects on Tvag were found. Tvag was elevated 0.24°C (5CE) and 0.35°C (10CE) during the daily first 5 h of cold-exposure (10CE = 5CE > control; P = 0.02) throughout the entire 21-d trial. During other times of the day there was no effect of treatment on Tvag but treatment × interval was significant (P ≤ 0.02) during the 6–10 h from initiation of cold-exposure when the 10CE group remained in the cold but the 5CE group had been returned to the outdoor pen. The Tvag of the 10CE and 5CE heifers was elevated at this time of day compared to control heifers, but only during the first 4 to 6 d (5CE) or 7 to 9 d (10CE) of the trial. These results indicate that thermoregulatory mechanisms that control core body temperature undergo habituation and the timecourse of habituation depends on the duration of daily cold- exposure. Resting heat production was unaffected by the two durations of cold-exposure examined (P = 0.55), suggesting that metabolic acclimation does not occur in response to intermittent cold-exposure of beef cattle. Key words: Beef heifers, vaginal temperature, resting heat production, environment, cold duration