OPERANT RESPONSES OF PIGS TO ATMOSPHERIC AMMONIA

The motivation of Duroc X Landrace pigs, Sus scrofa, to avoid acute ex posure to two concentrations of atmospheric ammonia was assessed using operant conditioning. On a fixed interval concurrent avoidance schedu le, where each response (root) made on one operant manipulandum was fo llowed by exposure to puffs of ammonia at 100 ppm, six food-motivated pigs initially avoided rooting for food reinforcement on the ammoniate d manipulandum; a control manipulandum, vented only with fresh air, wa s preferred instead (42 and 16 roots, five and 13 reinforcements respe ctively; P < 0.001 in each case). This initial aversion was followed b y rapid acclimatization over 20 daily sessions, each lasting for 90 mi n (P<0.001). The acclimatization was independent of an underlying redu ction in the number of roots (P = 0.033). On a variable interval passi ve avoidance schedule, 12 food-motivated pigs only received food reinf orcement in the presence of ammonia. Acute exposure to ammonia at a pe ak 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, respe ctively, P = 0.046; 43, 50 and 37 reinforcements respectively, P = 0.0 2). This aversion was stronger after repeated testing over eight daily sessions (P < 0.001), each lasting for 90 min, yet many roots were st ill made and reinforcements were received on each manipulandum. The in itial avoidance of 100 ppm ammonia under a concurrent operant conditio ning schedule was due to the irritant rather than novel effects of amm onia exposure. This aversion was however, weak. Ammonia at 100 ppm was not completely avoided and acclimatization was rapid. (C) 1998 Elsevi er Science B.V. All rights reserved.