Do domestic pigs in controlled environments contrafreeload?

Many experiments report that animals will work (lever press) for food in the presence of freely available identical food. This phenomenon has attracted the attention of applied ethologists because it seems to prove that animals have a need to express appetitive behavior. If this is the case, then it has implications for the provision of environmental enrichment for animals in captivity. In this experiment, we maintained 6 pigs in closed economy environments for three 120-hr choice periods in which they had continuous free access to operant and identical free food. In the experiment, we tested pigs using 2 different operant schedules, fixed ratio (FR) 5 and variable ratio (VR) 5. We used a VR schedule because many enrichment studies claim that unpredictability is an important characteristic that makes an enrichment device attractive. The results show that pigs exhibited a negligible level of contrafreeloading (M +/- standard error of the mean proportion = 0.05 +/- 0.01). Furthermore, there were no significant differences between FRs and VRs of reinforcement.