Pig ear skin temperature and feed efficiency: Using the phase space to estimate thermoregulatory effort

Mammalian skin temperature is often used as an indicator of health status but has also been used in animal production as a proxy measure for thermoregulatory effort or energy wastage. An animal with a higher skin temperature may also have a lower feed efficiency. With advances in technology it is now feasible to continuously record temperatures of livestock over protracted periods of time. In this study, the ear skin pig temperature was related to feed efficiency using phase space diagram methodology. Fourteen Landrace finishers (all male) housed in one pen over a week at relatively high temperatures (average temperature throughout the experiment 27 °C) were supervised. The date, time and amount of feed consumed per individual animals was monitored via an electronic feeding station. The number of visits to the feeding station was used as an indicator of physical locomotor activity. Each animal was weighed at the beginning and at the end of the experiment to calculate their feed efficiency. The areas of the phase space diagrams of skin temperatures were used to quantify the variability of the time temperature series. Two areas in the phase space were correlated with feed efficiency (r = 0.77) and physical locomotor activity (r = 0.53). An index was developed that includes both areas, which increased the correlation between the variability of ear skin temperature and feed efficiency to r = 0.85. This methodology could be used to help categorise pigs in terms of feed efficiency for rapid phenotyping.