Thermographical quantification of physiological and behavioral responses of group-housed young pigs

Young pigs 4 to 7 wk old (7-15 kg) were exposed to 20 factorial combinations of five air temperatures (20, 24, 28, 32, and 36 degreesC) and four air velocities (0.1, 0.5, 1.0, and 1.5 m/s). Infrared imaging (0.06 degreesC sensitivity) was used to simultaneously quantify postural pattern and surface temperature (T-s) of the pigs. Three postural indexes were evaluated for expressing thermal comfort level of the pigs: (1) ratio of occupied floor area (A(f)) to the total surface area of the pigs - index I-f ; (2) ratio of A(f) to its maximumpossible value - index I-m; and A(f) per 100kg body mass - index A(f(100)). The pigs shared common thresholds of postural indexes I-f = 0.20 similar to0.24 and I-m = 0.75 similar to0.84 and T-s of 34.5 similar to 36.3 degreesC for the thermoneutral zone (TNZ). in comparison, index A(f(100)) of TNZ was greatly dependent on pig age or size. Yhe numerical A(f(100)) of TNZ was greatly dependent on pig age or size. The numerical indexes (I-f and I-m) provide objective, quantitative assessment of thermal comfort of the pigs. Functional relationships were established between I-m and T-s. Moreover I-m was used to quantify the effects of air velocity on the effective environmental temperature of the pigs at cool to warm ambient temperatures.