# Daily Variation of Body Temperature: An Analysis of Influencing Physiological Conditions
###### Abstract  
The evaluation of thermoregulation in homeothermic animals is important for their health assessment. Body temperature is influenced by the circadian rhythm, which, through certain signals, is regulated by the suprachiasmatic nucleus. Temperature is collected by various methods; to reduce the invasiveness of rectal temperature sampling, considered the most accurate, infrared thermography has been used. The aim of the present review was to describe the circadian variability of average body temperature in several domestic animal species. In addition to variations due to the circadian rhythm, a number of conditions that can influence body temperature have also been studied. One example of this is exercise, which occurs in the case of domestic animals such as horses, dogs, and donkeys. In particular, it has been analysed in athletic horses, where, following intense exercise, the circadian rhythm of temperature is altered. The daily temperature variation during pregnancy and the neonatal period was also analysed. The circadian rhythm of temperature is influenced by the gestational period of sheep and goats, but this is affected differently depending on the type of species. The same is true for the neonatal period, in kids, lambs, and cattle, where the circadian rhythm is established at different times.  
circadian rhythm; homeothermia; domestic animals; rectal temperature 20  
temperature is extremely important; in general, it is possible to measure body temperature, and it has been since the 1800s that measured temperature repetitions have been carried out [1]. For data collection, the most accurate method is considered to be the rectal method, despite being invasive [1; 8; 9]. Body temperature can undergo various variations due to the influence of some environmental factors such as humidity, solar radiation, and ambient temperature [10]. The circadian rhythm of body temperature (Tb) is regulated by maternal rhythms before birth, while after birth, it varies between species. After birth, in lambs and foals, fluctuations in body temperature are detected one week after birth. In primates, on the other hand, rhythms of Tb are detectable from the second postnatal week or later [11]. The process of temperature regulation and oscillation is known as thermoregulation. In thermoregulation, the hypothalamus has the function of regulating heat loss and heat production to maintain a stable temperature range for each species. When the homeostasis regulated precisely by the various thermoregulatory mechanisms is altered, fever can be encountered. Fever is an acute phase response that the body may generate following an infection or systemic inflammation. The rise in temperature triggers neurological, endocrine, immunological, and metabolic changes in order to limit the body's damage [3]. Although some of these physiological processes are valid for all organisms, there are variables that must be taken into account and that vary between animals, including the accumulation of fat, fur, and the number of sweat glands and their functionality [12]. The homeostatic regulation of body temperature is a fundamental physiological process that ensures the stability of the immune system in birds and mammals. Secondly, the thermoregulatory system is a complete system that utilises behavioural and autonomic processes in integration with other physiological systems, including the cardiovascular system, including the implementation of vasodilation and vasoconstriction, or the digestive system with the production of saliva [13]. The aim of this study was to understand how the circadian rhythm of mean body temperature varies in different domestic species and by which conditions it is influenced (Figure 2).  
Figure 1: The circadian rhythm of some of the most important parameters in horses and how they are influenced. Acrophase times were specified.