Effects of intermittent cold exposure varying in intensity on core body temperature and resting heat production of beef cattle

Abstract

. 2001. Effects of intermittent cold exposure varying in intensity on core body temperature and resting heat production of beef cattle. Can. J. Anim. Sci. 81: 459-465. Crossbred beef heifers (n = 18) fed at 1.3× maintenance were exposed to summer daytime temperatures (20 ± 0.2°C) for 8 h (08:00 until 16:00) and to control (22°C), moderate (-6°C) or cold (-15°C) environments for 16 h daily (16:00 until 08:00) for a minimum 21-d adaptation period to investigate the effects of intensity of intermittent cold exposure on vaginal temperature and resting heat production. Resting heat production was measured at the end of the adaptation period. Vaginal temperature was continuously monitored throughout the experiment using radiotelemetry. Vaginal temperature increased immediately after the onset of cold exposure in both moderate and cold treatments, peaked after 3 h, and returned to pre-exposure levels by the time the 16-h treatment ended. In contrast, vaginal temperatures of control heifers peaked only after feeding at 08:30. Treatment did not affect daily maximum (P = 0.60), mean (P = 0.72) or minimum (P = 0.34) vaginal temperatures, but heifers in both cold-exposed treatments spent more time (P = 0.03) with vaginal temperatures exceeding the daily mean vaginal temperature than control heifers. Compared to control heifers, the variability of vaginal temperature increased 1.8-and 2.2-fold in the moderate and cold treatments, respectively (P = 0.04), and did not change with time (P = 0.98). Resting heat production did not increase following 21 d of exposure to moderate and cold conditions. Results of this study indicate that intermittent cold exposure influenced circadian body temperature rhythms without increasing resting heat production. exposition intermittente au froid sur la température vaginale et sur la production de chaleur au repos, mesurée à la fin de la période d'adaptation. La température vaginale a été vérifiée en permanence par radiotélémétrie. La température vaginale augmente immédiatement avec l'exposition au froid, tant avec le froid modéré que le froid intense, atteint un plateau au bout de 3 heures et revient à la température initiale au terme des 16 heures du traitement. La température vaginale des sujets témoins, en revanche, n'atteint un plateau qu'après la ration de 8 h 30. Le traitement n'a aucune incidence sur la température maximale (P = 0,60), moyenne (P = 0,72) ou minimale (P = 0,34) quotidienne dans le vagin, mais la température vaginale des génisses des deux groupes exposés au froid demeure plus longtemps (P = 0,03) au-dessus de la température moyenne que chez les sujets témoins. Comparativement au groupe témoin, les génisses soumises à un froid modéré et à un froid intense voient la variabilité de leur température vaginale multipliée de 1,8 et de 2,2, respectivement (P = 0,04), sans variation dans le temps (P = 0,98). La production de chaleur au repos ne s'accroît pas après les 21 jours d'exposition à un froid modéré ou intense. Les résultats de l'étude indiquent qu'une exposition intermitt...

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

“…In fact, the ∆T vag for all treatments in the present study were 50 to 60% higher than the control value (2.47°C) of our previous study (Bergen et al 2001). High control room temperature in the present study (27.1°C) compared with that (21.8°C) of Bergen et al (2001), coupled with cool outdoor nighttime temperatures (Fig.…”

“…When overall means were compared, there was no effect of interval or treatment on MeanT vag , MaxT vag or MinT vag (P ≥ 0.49; Table 1) as was also the case in our previous study (Bergen et al 2001) where beef heifers were exposed to 21.8, -6.3 or -15.2°C for 16 h d -1 for 21 d. However, whereas no effect of cold-exposure on HoursOver and ∆T vag (P ≥ 0.29; Table 1) was found in the present study, we (Bergen et al 2001) found previously that these parameters were both elevated with each of the two cold-exposure treatments. In fact, the ∆T vag for all treatments in the present study were 50 to 60% higher than the control value (2.47°C) of our previous study (Bergen et al 2001).…”

“…The NE m is predicted to be increased by 1% for every 1°C drop in temperature below 20°C [National Research Council (NRC) 1996]. While this may be the case when the cold-exposure is continuous throughout the day, Bergen et al (2001) and Graham et al (1981) found no change in resting heat production in beef heifers and sheep, respectively, coldexposed indoors for only part of each day. An increase in heat production was expected in these studies, based on the mean daily temperature of the treatment environments.…”

“…Heifers were moved in pairs to the stanchions and calorimetry hoods in the control room approximately 12 h post-feeding and RHP was measured for 5 h (1000 to 1500). (Bergen et al 2001).…”

“…This was originally suggested by Slee (1971) in reviewing numerous sheep adaptation studies where the nature of the adaptation seemed to depend on "mode of administration and dosage" of cold. Environmental temperature variability may impact adaptation through induction of variability in temperature of the body core (T core ) as Bergen et al (2001) also showed that exposure of beef heifers to cold temperatures during only part of the day resulted in increased variability, but not the mean of T core . In comparison, continuous cold exposure throughout the day has been shown to reduce (Young 1975), increase the variability of (McLean et al 1984) or have no effect on T core (Lefcourt and Adams 1998).…”