Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/1998
Publication Date: N/A
Citation: Interpretive Summary: Production efficiency in feedlots decreases in the winter. Generally, steers need to eat more just to stay warm. However, even when addition feed is provided, rates of weight gain during winter are less than during warmer periods. The reduced rates of gain probably reflect a change in the mechanisms regulating metabolism. To examine how cold affects regulation of metabolism in steers, we investigated the influence of cold ambient temperatures on body temperature. Little is known concerning regulation of body temperature of cattle under conditions of low ambient temperatures. In this study, body temperatures of feedlot steers were monitored for 2 winters in Nebraska, from late-December to mid-March in year 1 and from late-December through June in year 2. Body temperatures exhibited a daily rhythm with the low point around 0800 h and the high point around 1900 h. For years 1 and 2, daily high (40.1 and 39.7 deg. C), low (38.8 and 38.6 deg. C), and average (39.3 and 39.1 deg. C) body temperatures were not affected by ambient temperatures. However, sharp peaks in body temperature were often seen in the evening, normally 30 to 60 min after dusk. These peaks seldom occurred when average daily ambient temperatures were less than -7.5 deg. C. This finding suggests that animals severely restrict energy expenditures when average ambient temperatures fall below -7.5 deg. C. More research is needed to determine if this is the explanation for why weight gains are reduced in the cold and to determine the potential economic benefits of providing shelter for animals exposed to cold.
Technical Abstract: Little is known concerning regulation of body temperature of cattle under conditions of low ambient temperatures. To investigate the influence of cold ambient temperatures on body temperature regulation, core body temperatures of feedlot steers were monitored for 2 winters in Nebraska, from late-December to mid-March in year 1 and from late-December through June in year 2. In year 1, radiotransmitters to monitor temperature were implanted in the peritoneum of 5 steers (360 Kg); in year 2, 4 steers (320 Kg) were used. Body temperatures and ambient temperatures were recorded at 3-min intervals and mathematically filtered to produce 120 readings/d. For years 1 and 2, daily maximum (40.09 and 39.66 C), minimum (38.78 and 38.64 C), and average (39.29 and 39.06 C) body temperatures were not affected by ambient temperatures. Body temperatures exhibited a circadian rhythm with the minima around 0800 h and the maxima around 1900 h. For both years, sharp peaks in body temperature were often seen in the evening and, for year 2, to a lesser extent in the morning. The occurrence of peaks was normally congruent, within a 1.5 h window, across steers. Congruent peaks in the evening with peak heights of 1.05 and .77 C occurred on 65% and 56% of days in years 1 and 2, respectively. Occurrence of congruent peaks was found to be correlated to dusk; peaks followed dusk by 30 to 60 min. Ambient temperature also influenced the occurrence of peaks, with few peaks observed when average daily ambient temperatures were below -7.5 C. The dynamic changes in body temperature throughout the day, including the peaks in body temperature after dusk, strongly suggest that thermoregulatory systems in steers respond not only to current ambient conditions, but also to more integrative measures such as day length and daily heat load.