Thermoregulation in pronghorn antelope (Antilocapra americana, Ord) in winter

Conservation of energy is a prerequisite thermoregulatory strategy for survival in northern hemisphere winters. We have used thermistor/data logger assemblies to measure temperatures in the brain, carotid artery, jugular vein and abdominal cavity, in pronghorn antelope to determine their winter body temperature and to investigate whether the carotid rete has a survival role. Over the study period mean black globe and air temperature were -0.5+/-3.2 degrees C and -2.0+/-3.4 degrees C, respectively, and mean daytime solar radiation was approximately 186 W m(-2). Brain temperature (T(brain), 39.3+/-0.3 degrees C) was higher than carotid blood temperature (T(carotid), 38.5+/-0.4 degrees C), and higher than jugular temperature (T(jugular), 37.9+/-0.7 degrees C). Minimum T(brain) (38.5+/-0.4 degrees C) and T(carotid) (37.8+/-0.2 degrees C) in winter were higher than the minimum T(brain) (37.7+/-0.5 degrees C) and T(carotid) (36.4+/-0.8 degrees C) in summer that we have reported previously. Compared with summer, winter body temperature patterns were characterized by an absence of selective brain cooling (SBC), a higher range of T(brain), a range of T(carotid) that was significantly narrower (1.8 degrees C) than in summer (3.1 degrees C), and changes in T(carotid) and T(brain) that were more highly correlated (r=0.99 in winter vs r=0.83 in summer). These findings suggest that in winter the effects of the carotid rete are reduced, which eliminates SBC and prevents independent regulation of T(brain), thus coupling T(brain) to T(carotid). The net effect is that T(carotid) varies little. A possible consequence is depression of metabolism, with the survival advantage of conservation of energy. These findings also suggest that the carotid rete has wider thermoregulatory effects than its traditional SBC function.