Skin and core temperatures as determinants of heat production and heat loss in the goat

Abstract

In 82 experiments on 10 goats body core temperature (Tcore) was altered between 35 degrees and 42 degrees C by external heat exchangers acting on blood temperature while skin temperature (Tskin) was maintained constant, by a circulating shower bath, at different levels between 32 degrees and 44 degrees C. At all skin temperatures at least fourfold increases of heat production (M) and respiratory evaporative heat loss (REHL) occurred when Tcore was lowered or raised, respectively. The lower Tskin was, the higher were the thresholds of Tcore, at which M or REHL exceeded resting levels. The lower Tskin was, the higher were the slopes, at which M or REHL changed per unit of Tcore. At a given Tskin, the slopes decreased with increasing M or REHL, and were dependent on the range of Tcore. The higher the range of Tcore, the steeper changed M and REHL with changing Tcore, if all other variables were held constant. The results support the concept that an exponential relationship between Tcore and the rate of core temperature signals is the primary cause of the effects exerted by Tskin on the slopes, at which M or REHL change per unit of Tcore.

The metabolic response to skin temperature

“…Its efficiency and limits to produce a constant and spatially homogeneous skin temperature have been discussed in detail by Nagel et al (1986) …”

“…Mean values and standard deviations were 38.34 • 0.33~ (n = 25). The animals then entered a shower bath the details of which have been described before (Nagel et al 1986). After the heat exchangers and the measuring probes were attached, the bath was filled with water the temperature of which was controlled manually within 0.1~ at any desired level.…”

“…Silastic tubes were connected to a common carotid artery and an external jugular vein and exteriorized at the neck. The technique followed that proposed by Dennis et al (1974) and was described in detail by Nagel et al (1986). Patency of the shunts was ensured by permanent treatment with phenprocoumon.…”

“…The experiments reported below were done to assess that fraction of the metabolic response to cold which can be attributed to skin temperature. This question has been dealt with in a number of previous investigations (for review see Simon et al 1986), including two from our own laboratory (Jessen 1981 ;Nagel et al 1986). In these studies, however, the influence of skin temperature on the metabolic response was regularly deduced from multiple regression analysis or from its effects on core temperature thresholds.…”

Thermosensitivity of the goat's brain.

“…The linear regressions were used for the sake of comparison only, and are not meant to imply that the relationships between temperature and effector responses are linear (see Nagel, Herold, Roos & Jessen, 1986). In eleven periods of hypothalamic cooling (1) the slopes of M over Thypo varied between -075 and -2-84 W/ (kg°C) and had a mean value (± standard deviation) of-141+ 0 74 W/(kg°C).…”