# Quantification of the Area of the Highest Temperature in
## 1 Introduction  
Similar to other objects, animal bodies radiate power that can be detected with specific tools. Thermographic cameras enable measurements of radiated energy, providing data about the surface temperature [1; 2]. The amount of detected energy depends on many internal and external factors. Of the internal factors, the local increase in blood flow, increased tissue metabolism, and sweating can affect the infrared images, which offer the opportunity for diagnostic use. Of the external factors, ambient temperature, wind, humidity, and dirt play significant roles [1; 2; 3]. The basal metabolism of younger individuals is higher than that of adults, resulting in increased surface energy radiation [4]. This can be associated with the fast growth and development of muscles, but also with high motoric activity [5]. It was found that metabolism is associated with heart rate, making it a possible tool for metabolic rate evaluation [4]. In foals less than one month of age, cardiac output and respiration are not yet stabilized, which causes variations in both heart and respiratory rates. Also, heart ratemeasurement requires contact with the animal, which can induce a stress response and increase the measured values, meaning the result is then biased [4; 5; 6]. While there are helpful recommendations for nutrition in equines, they are not always precise as individuals vary [7]. This may result in malnutrition and maldevelopment of the growing foal. The main differences are found in housing systems and health conditions. Foals can be housed in low temperatures (open housing in colder climates), but they require an acclimatization period to maintain their health. But even then, their metabolic rate can be twice that of foals housed in a closed system, resulting in significantly higher nutritional demands, as maintenance demands exceed growth demands [4; 6; 8; 9; 10; 11]. On the other hand, in sick foals, in which nutrient intake is decreased because of a disease, metabolic rates decrease, hampering proper growth [4]. Thus, proper evaluation of the nutritional demands of the individual foal can be challenging, as thermoregulation plays a major role in maintenance demands. The underestimation of demand increase will affect the growth process, especially at a younger age. Thus, expenses on foal homeothermy should be considered, but they are difficult to measure [7; 8; 10]. In grown horses, similar concerns arise, as housing, the training regime, and sport performance also cause variations in maintenance demands. Malnutrition in adults does not hamper growth and proper cartilage development; however, refeeding is still challenging, especially in older individuals [12; 13]. Apart from increased metabolism, other features of young animals affect their thermoregulation. While insulation is provided by body fat and hair coat, fat tissue and effective hair coat develop with age, resulting in increased radiation [14; 15]. This suggests that energy losses in foals are higher than in adults in similar ambient temperatures. Another factor having a big impact is the increased surface-area-to-weight ratio in young animals [8; 16]. On the other hand, during training and in older horses, the emission of excessive heat is a big challenge. Ageing is also responsible for less effective cooling, and proper hydration, allowing for sweating, should be supplied for all [10; 17]. Energy emission can be measured not only on animals but also on inanimate objects. Thus, radiation from nearby objects may affect the animal's measurements, especially in higher than ambient temperatures, which can occur with sun exposure. Air humidity, as well as the presence of dust, will also affect thermographic results, especially with an increasing distance from the examined objects [18]. Regardless of the aim, thermal images are also affected by the roughness of the examined surface, providing more precise results from smooth surfaces. Thus, in achieving credible and accurate thermographic images, experience, effort, and consequence are crucial [3; 18; 19].