Thermal behaviour of growing pigs in response to high temperature and humidity

The effects of high ambient temperatures and humidities on thermal behavioural adaptation and pen fouling of group-housed growing pigs were assessed. Twelve groups of 10 gilts of an average initial body weight (BW) of 61.7 kg were used. During nine experimental days, ambient temperatures were increased by two degrees per day from 16 °C on day 1 to 32 °C on day 9 and fixed at one of three levels of relative humidity (RH) 50, 65, and 80%. Space allowance per pig was 1 m2. The floor was 60% solid and 40% slatted. Lying, excreting and fouling behaviour were studied using video recordings. During the nine trial days a radar activity meter was used to record the physical activity of each group of 10 pigs every 6 min. A regression model was used to calculate the heat produced by activity from total heat production (HP). The lying position of the pigs was classified, e.g. Lateral, Sternal, Half lateral lying. Excreting behaviour was determined in terms of, e.g. urination and defecation. Furthermore, thermoregulatory lying behaviour (huddling and wallowing) were recorded. All behaviours were determined in terms of frequency and location. Temperature affected lying and excretion behaviours. The number of pigs lying on slatted floor increased with increasing temperature (p <0.001). The inflection point temperature (IPt) for the pigs to lie on slatted floor was on average 18.8 °C; below this IPt the pigs remained lying on the solid floor. The heat produced by activity was relatively constant below 24.2 °C, but once this IPt had been exceeded it down turned. Temperature was inversely related to huddling (p <0.001) and positively related to wallowing (p <0.001). The total excretions on solid floor increased with temperature (p <0.05). The number of urinations was inversely related to temperature (p = 0.13). However, the relative number of urinations on the solid floor increased concomitantly with temperature (p <0.05). It can be concluded that high temperatures greatly affect lying and excreting behaviour. At a relatively low temperature, pigs preferred to lie on the slatted floor. At high temperature, there was a clear increase in fouling of the solid floor. At high humidity, changes in behaviours occurred at lower temperatures