On the rewarding nature of appetitive feeding behaviour in pigs ( Sus scrofa): Do domesticated pigs contrafreeload?

Contrafreeloading is the phenomenon that animals prefer to “work” for food even though “free” food is available nearby. In this study, we investigated whether pigs express contrafreeloading in a test situation where the searching, finding and consuming of food items resembles a natural foraging situation. For that purpose, we investigated whether pigs prefer an environment with straw and hidden food rewards (chocolate raisins) to an environment with straw, but without hidden food rewards and with food rewards “freely” available in a trough. Preference behaviour was investigated in a Conditioned Place Preference task (CPP). Typically, CPP measures the conditioned preference in the absence of reinforcers so that unwanted interference with the reinforcers during testing does not take place. The results show that (a) CPP can be used to establish the preference of pigs for different environments (experiments 1–4); (b) that pigs prefer to forage for food over “freely” available food from a trough (experiment 3) and (c) that anticipating a food reward has reinforcing effects above and beyond the reinforcing effects of acquisition of a food reward alone (experiment 4). The results therefore show that pigs express contrafreeloading when using a natural foraging task and they suggest that the reinforcing effects of anticipation, which occurs during natural foraging in the delays between searching and finding food, may contribute to the observed expression of contrafreeloading in pigs.