Abstract
Pigs were trained to obtain food by pressing a panel with their snouts. Pairs or trios of animals were tested together with the panel widely separated from the feeding bowl and response rates were examined in relation to social dominance. Dominant animals of the pairs usually did almost all the panel pressing whether the pair lived together or apart. In pairs tested together with only one member trained, the untrained pigs did not learn to respond. In trios tested for 10 min, the dominant pigs did not press most but, if one animal was satiated before testing, the dominant pigs in the remaining pairs tended to press more. In trios tested for 3 h one pig pressed most and this was unrelated to rank.
https://www.sciencedirect.com/science/article/abs/pii/0003347279900332