Physiological and Behavioral Mechanisms of Thermoregulation in Mammals

Abstract

This review analyzes the main anatomical structures and neural pathways that allow the generation of autonomous and behavioral mechanisms that regulate body heat in mammals. The study of the hypothalamic neuromodulation of thermoregulation offers broad areas of opportunity with practical applications that are currently being strengthened by the availability of efficacious tools like infrared thermography (IRT). These areas could include the following: understanding the effect of climate change on behavior and productivity; analyzing the effects of exercise on animals involved in sporting activities; identifying the microvascular changes that occur in response to fear, pleasure, pain, and other situations that induce stress in animals; and examining thermoregulating behaviors. This research could contribute substantially to understanding the drastic modification of environments that have severe consequences for animals, such as loss of appetite, low productivity, neonatal hypothermia, and thermal shock, among others. Current knowledge of these physiological processes and complex anatomical structures, like the nervous systems and their close relation to mechanisms of thermoregulation, is still limited. The results of studies in fields like evolutionary neuroscience of thermoregulation show that we cannot yet objectively explain even processes that on the surface seem simple, including behavioral changes and the pathways and connections that trigger mechanisms like vasodilatation and panting. In addition, there is a need to clarify the connection between emotions and thermoregulation that increases the chances of survival of some organisms. An increasingly precise understanding of thermoregulation will allow us to design and apply practical methods in fields like animal science and clinical medicine without compromising levels of animal welfare. The results obtained should not only increase the chances of survival but also improve quality of life and animal production.

Clinical Applications and Factors Involved in Validating Thermal Windows Used in Infrared Thermography in Cattle and River Buffalo to Assess Health and Productivity

“…This effect can also be seen in black and white cows that present greater absorption of solar radiation, though to a lesser degree than buffaloes during hot periods. However, in addition to color, coat thickness (and its transmittance), is another factor that can condition the amount of energy that is transferred along the fur and reaches the epidermis [6,7,9,103] (Figure 9). As a result, buffaloes must dissipate heat by lying in swampy areas or mud for long periods [21,99,108], especially during the hot season.…”

“…In the river buffalo, increases in the environmental temperature trigger physiological and behavioral responses (i.e., wallowing and muddying in water or seeking shade) when the peripheral and central thermoreceptors perceive changes in climatic conditions [ 96 , 97 ]. These behaviors serve to efficiently thermoregulate the animal through the vasodilatation of a large number of blood vessels in the skin [ 6 , 9 , 98 , 99 ]. However, buffaloes are particularly susceptible to heat stress especially when exposed to direct sunlight, due to their dark skin with high absorbance and transmittance and deficient dermal mechanisms for dissipating latent heat, [ 6 , 7 , 21 , 100 , 101 , 102 ].…”

“…This technique detects the heat irradiated by a surface, decoding it into a temperature by a biological body, and interpreting its relation to the state of animal comfort [5]. In terms of both physiological and practical mechanisms, the principal mechanism involved in heat gain or loss is the regulation of the diameter of near-surface blood vessels; that is, the cutaneous vasodilatation that occurs in anatomical regions to permit thermal exchanges with the environment [6][7][8][9][10][11]. These regions, known as thermal windows [12][13][14][15][16], are characterized by a dense network of blood vessels, the presence of plexus, arteriovenous anastomosis, and the absence of hair [7,8].…”

“…From a physiological perspective, changes in blood flow are essential because they permit thermal exchange between an animal’s skin and the environment through vasoconstriction and vasodilatation controlled by the sympathetic noradrenergic vasomotor response of the smooth muscles [ 24 ]. Adopting this approach has improved our understanding of the thermoregulation strategies characteristic of different species under cold conditions, such as reduction in the size of the tail and ears in some animals, the tails of laboratory rats, or the digital pads ( torus digitalis ) of cats, all of which function as thermal windows that can dissipate heat [ 9 , 20 , 25 , 26 , 27 ]. However, analyses conducted in this field led us to question the usefulness and viability of the thermal windows currently suggested for large ruminants, since certain anatomical aspects—hair, skin color or the lack of it, and skin thickness—can affect specific thermal windows, making them unviable in these species, though they are effective in others [ 21 , 28 ].…”

Pathophysiology of Fever and Application of Infrared Thermography (IRT) in the Detection of Sick Domestic Animals: Recent Advances

“…Despite this, some still question whether their study helps measure pathologies, in spite of the fact that scientific evidence indicates that it can be used for their detection [ 2 , 4 ]. However, given the scarcity of quantitative, studies of non-invasive tools that allow us to understand and interpret the pathophysiological processes of fever in farm animals are still valid [ 5 , 6 ].…”