REACTIONS OF PIGS TO A HOT ENVIRONMENT

When compared to other species of farm animals, pigs are relatively sensitive to highenvironmental temperatures because the pig cannot sweat and is relatively poor at panting. Littleinformation is available about the ambient temperatures above which group-housed pigs start toadapt their mechanisms of balancing heat loss and heat production. The temperature above whichan adaptive response occurs (also called the critical temperature or inflection point temperature)may well differ depending on which physiological or behavioral parameter is studied. Theobjective of these studies was to determine the reactions of pigs to a hot environment(experiment 1) and to study the effects of different cooling systems (sprinklers and water bath)on behavioral, physiological and productive parameters (experiment 2). In experiment one 12groups of 10 pigs of 60 kg were studied in respiration chambers. Each day, the temperature wasincreased by 20 C from low (160 C) to high (320 C). In experiment two 12 groups of 5 pigs werestudied under the humid tropical climate of Viet Nam. The pigs first visible reaction toincreasing ambient temperature was a change in behavior. Wallowing was the first of allbehavioral changes. It occurs at relatively low ambient temperature: from 16 to 170 C. The firstphysiological reaction to high ambient temperatures was an increase in respiration rate; onaverage this occurred at 22.40 C. An increase in rectal temperature occurred above an averageambient temperature of 26.10 C. This implies that pigs can prevent an increase in their bodytemperature for an ambient temperature range of about 3.70 C. An increase in rectal temperatureand an extra reduction in feed intake are indicators that room temperature is clearly above theupper limit of the thermal neutral zone. Pigs in pens with sprinklers or water bath had lowerrespiration rate and skin temperature than pigs in control pens, especially during the hot period ofthe day in pens with outside yard. No effect of cooling on the rectal temperature was found.Pigs in pens with outside yard without cooling were less active than pigs in cooling pens. Pigs incontrol pens were lying more in lateral position than pigs in the cooled pens. Pigs in pens withsprinklers had the highest feed intake and the highest daily gain.

It is concluded that the availability of cooling systems reduces heat stress in pigs. The indicatorsof heat stress found in this study could be used as set points for these cooling systems, in order toimprove animal performance and welfare in hot conditions.