In most endothermic homeotherms, core body temperature follows a circadian rhythm. This review focuses on the amplitude of the circadian rhythm of body temperature (CRT) because the amplitude of the CRT has received increasing attention in the last few years. First, we discuss the methodology that can be used to measure the CRT, and the methodology used to calculate the amplitude of the CRT. Then, we illustrate the effect of changes in the external and internal environments on the amplitude of the CRT. Quite interestingly, as illustrated in this paper, while the molecular and hormonal basis of the CRT is well understood, the control of the amplitude is not. We conclude that challenges in the capacity of the animal to thermoregulate, or to manage energy, can impact on the amplitude of the CRT.

Protein restriction in utero may give rise to restricted growth as well as induce metabolically related diseases. In order to determine the suitability of mink as an animal model for metabolism studies, the effects of protein restriction during gestation on dam and kit performance must first be determined. Mink dams were fed an adequate protein (AP; crude protein:fat:carbohydrate ratio of 31:55:14% of metabolizable energy, ME) or a low protein diet (LP; 19%:49%: 32% of ME) during the last 21.2 ± 3.3 days of gestation, followed by an adequate diet during lactation. Respiration and balance experiments were performed during late gestation and twice during lactation. The dietary treatment only affected energy metabolism traits significantly during the treatment period in late gestation, such that LP dams oxidized less protein (12% vs 23% of heat production, HE, P = 0.001) but more carbohydrate (37% vs 26% of HE, P < 0.05), and retained less nitrogen (0.3 vs 0.4 g.kg^-0.75.day^-1, P < 0.05) than AP dams. Reproductive performance and kit organ growth were not affected by diet. Kit losses up to weaning were higher in LP than AP dams (2.0 vs 1.4, P < 0.05). LP fetuses weighed less (8.3 vs 11.6 g, P < 0.001) and were shorter (6.2 vs 7.6 cm, P < 0.001) than AP fetuses, however, differences might have been due to different implantation times. LP kits weighed 8.5% less than AP kits at birth, and remained lighter until 21 days of age. The LP diet caused growth restriction and increased kit mortality indicating that the dietary protein supply during late gestation was suboptimal to re-quirements. The long-term consequences of protein restriction in utero in terms of permanent metabolic changes in adulthood now need to be investigated

Panting is a mechanism that increases respiratory evaporative heat loss (REHL) under heat load. Because REHL uses body water, it is physiologically and ecologically relevant to know under what conditions free-ranging animals use panting. We investigated whether the cranial arterio-venous temperature difference could provide information about REHL. We exposed sheep to environments varying in ambient dry bulb temperatures (Env 1: ~15°C, Env 2: ~25°C, Env 3: ~40°C, Env 4: ~40°C + infrared radiation) and measured REHL simultaneously with carotid arterial (T (car)) and jugular venous (T (jug)) blood temperatures, as well as brain (T (brain)) and rectal (T (rec)) temperatures. REHL increased significantly with ambient temperature, from 18.4 ± 4.5 W at Env 1 to 79.5 ± 12.6 W at Env 4 (P < 10(-6)). While there was no effect of environment on T (car) (P = 0.7) or T (jug) (P = 0.09), the difference between them (T (a-v) = T (car) - T (jug)) increased from Env 1 to Env 2 (P = 0.04) and from Env 3 to Env 4 (P = 0.008). T (a-v) reached a maximum of 0.7 ± 0.2°C at Env 4 and was positively correlated with REHL across environments (r (2) = 0.78, F = 34.7, P < 10(-3)). Calculated cranial blood flow changed only from Env 2 to Env 3 (P = 0.002). The increase in REHL maintained homeothermy when dry heat loss decreased. While REHL could increase without generating an increase in T (a-v), any increase in T (a-v) was always associated with an increase in REHL. We conclude that the cranial T (a-v) provides useful information about REHL in panting animals.

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