Operant responses of pigs to atmospheric ammonia

Abstract

The motivation of Duroc×Landrace pigs, Sus scrofa, to avoid acute exposure to two concentrations of atmospheric ammonia was assessed using operant conditioning. On a fixed interval concurrent avoidance schedule, where each response (root) made on one operant manipulandum was followed by exposure to puffs of ammonia at 100 ppm, six food-motivated pigs initially avoided rooting for food reinforcement on the ammoniated manipulandum; a control manipulandum, vented only with fresh air, was preferred instead (42 and 16 roots, five and 13 reinforcements respectively; P<0.001 in each case). This initial aversion was followed by rapid acclimatization over 20 daily sessions, each lasting for 90 min ( P<0.001). The acclimatization was independent of an underlying reduction in the number of roots ( P=0.033). On a variable interval passive avoidance schedule, 12 food-motivated pigs only received food reinforcement in the presence of ammonia. Acute exposure to ammonia at a peak concentration of either 40 or 100 ppm did not influence the overall amount of food consumed ( P>0.05). However, significantly more roots were made and more food reinforcements were received in fresh air and 40 ppm ammonia than in 100 ppm ammonia (345, 365 and 241 roots, respectively, P=0.046; 43, 50 and 37 reinforcements respectively, P=0.02). This aversion was stronger after repeated testing over eight daily sessions ( P<0.001), each lasting for 90 min, yet many roots were still made and reinforcements were received on each manipulandum. The initial avoidance of 100 ppm ammonia under a concurrent operant conditioning schedule was due to the irritant rather than novel effects of ammonia exposure. This aversion was however, weak. Ammonia at 100 ppm was not completely avoided and acclimatization was rapid.