# Daily Variation of Body Temperature: An Analysis of Influencing Physiological Conditions
## 3 Some Factors Affecting Body Temperature and Its Circadian Rhythm
### Circadian Rhythm of Temperature following Exercise
A relationship has been noted between increased temperature detected with IRT and hypothalamic-pituitary-adrenal activity and a consequent release of cortisol [50]. The use of the thermal imaging camera is considered innovative, as it reduces the risk of infection and stress caused, for example, by manipulation, as it is not necessary to touch the subject [54; 55]. The latter is used to measure infrared radiation by creating maps of the temperature produced by the mammal [56]. Regarding the influence of operation on temperature, according to [PERSON] et al. [5], temperature changes during exercise and is also influenced by the time of exercise. In fact, it appears that the temperature increases more in the afternoon. In fact, the surface temperature (ST) increases during exercise; there is a small difference between the body and the surface temperature of 8 \({}^{\circ}\)C at rest and 4 \({}^{\circ}\)C during exercise. Other studies [57], on the other hand, show that the temperature increased without immediately returning to the control parameters. In fact, for this study, nine horses were used, whose temperature was always taken in the early morning hours (6:00 a.m.) once every week. The temperature was measured in certain areas of the body, such as the fore and hind limbs and the back. Compared to these areas, the results show an increase of approximately 12.3 \({}^{\circ}\)C, of which the lowest temperature was 6.9 \({}^{\circ}\)C to 19.2 \({}^{\circ}\)C. In addition to the time of day, the temperature also tends to vary depending on the type of work being done. In fact, as shown in [48], if a medium-sized horse (500 kg) performed moderate work for 60 min, the temperature would rise and increase by approximately 15-18 \({}^{\circ}\)C. During a running activity, on the other hand, for a horse of the same size but an activity considered shorter, the temperature would increase by only 5 \({}^{\circ}\)C. However, this can negatively affect homeostasis and, thus, the animal's metabolism and performance. For this not to happen, the temperature increase should be a maximum of 2 \({}^{\circ}\)C. There must therefore be a balance between heat dissipation and temperature maintenance [46]. With respect to the above, some work using an infrared camera confirmed an increase in skin temperature in correlation with training intensity. Studies [46; 58] show that athletic Thoroughbred horses have a specific daily rhythm of activity in temperature regulation. This is also confirmed by actograms, which show activity in most cases during the day. With respect to the daily rhythmicity of body temperature, [PERSON] et al. [20] report that a daily rhythmicity of body temperature was found in considered athletic horses considered. In particular, the results show a 24 h peak in the periodograms about a twice-daily measurement. The measurement was taken one hour before the exercise and two hours after the end of the exercise; the temperature was also taken during the rest day (considered a control). Compared to the control, the temperature showed an increase of 0.7 \({}^{\circ}\)C during the exercise but then returned to the rest day values two hours after the end of the exercise. In relation to the above, the rectal temperature measured during the resting day reflected the circadian oscillation of the temperature, which varied due to exercise. A further article by [PERSON] et al. [20] confirms a robust daily temperature rhythm in athletic horses. According to a comparison, the daily temperature rhythm was influenced by exercise; the temperature was found to increase compared to sedentary horses. In a comparison of sedentary horses, athletic horses, and athletic horses two weeks after exercise, [PERSON] et al. [59] show that all groups, despite exercise, maintain the circadian temperature rhythm unchanged, showing nocturnal acrophase between 22:04 and 22:48. Dogs can also be considered valuable study models for understanding temperature variation in the daily rhythm.