Trade-off between ammonia exposure and thermal comfort in pigs and the influence of social contact

The trade-off made by pigs between exposure to a concentration of ammonia g as recorded in commercial piggeries and thermal comfort was observed in two chronic choice tests. In the first experiment, eight pigs which were paire d and eight pigs which were held as singles, were forced to choose between compartments of a preference chamber that were polluted with an ammonia gas concentration of 40 p.p.m, and heated with a 750 W radiant heater or compa rtments that were unpolluted and unheated, for 8 days. The location of the choice options teas switched after 4 days to eliminate positional bins. Air temperature ranged from 0.5 degrees C to 15.0 degrees C. in the second exp eriment, eight pigs held as pairs, were free to choose between compartments that were polluted with an ammonia gas concentration of 40 p.p.m. and heat ed with a 750 W radiant heater, polluted and unheated, unpolluted and heate d and unpolluted and unheated, for 14 days. The location of the choice opti ons was switched after 7 days to eliminate positional bias. Air temperature ranged from 4.0 degrees C to 24.0 degrees C. AIL compartments contained fo od and water ad libitum; wood shavings were used as bedding material. bl bo th experiments, the location of all pigs was scan sampled every 15 min and their behaviour at this time was recorded instantaneously. Location and beh aviour were compared against air temperature. In the first, forced choice e xperiment, the pigs preferred the heated-polluted compartments when air tem perature was less than the estimated lower critical temperature (LCT) (P < 0.001). As air temperature approached the estimated LCT, the pigs occupied the unheated-unpolluted compartments move often. Overall each visit made to the heated-polluted compartments lasted significantly longer at 265 min (p aired), 208 min (single) than visits to the unheated-unpolluted compartment s at 29 min (paired), 31 min (single) (P < 0.001). Although they could have huddled to conserve hear, the paired pigs spent less time? overall, in the unheated-unpolluted compartments (P < 0.001). When air temperatures were l ower than the estimated LCT, the pigs huddled together but as air temperatu re increased, the pigs spent more time resting apart (P < 0.001) in the hea ted-polluted compartments. It is suggested that the paired pigs were motiva ted to remain in the heated-polluted compartments for companionship rather than thermal comfort. In the second, free choice experiment, the pigs prefe rred to remain in the unpolluted compartments, adjusting their occupancy of the heated and unheated compartments as ambient air temperature decreased or increased above the estimated LCT (P < 0.001). The pigs made fewer visit s to the polluted compartments and each visit was shorter, at 44 min (P < 0 .001). Visits to the unpolluted compartments lasted for 291 min. It is sugg ested that the delayed aversion shown to ammonia in both experiments was du e to a progressive sense of malaise. However, both experiments indicated th at this delayed ammonia aversion was weaker than preference for thermal com fort.