Foraging in the domestic pig, sus scrofa  (Page 5/7)

Held et al. found evidence to support their hypothesis. The informed pigs were capable of remembering and relocating buckets of food. When given access to empty buckets and buckets with food that they had been shown previously, they showed a significant preference for the food-filled buckets. When the larger, more dominant pigs were paired with the informed pigs, they inspected food buckets that had just been visited by the informed pigs more often than would be expected by chance. In over half the trials, the dominant pig displaced the informed pig from the bucket it was investigating, which was statistically significant. Non-informed dominant pig spent less time searching for food when paired with an informed subordinate pig than when they foraged alone. Thus, dominant pigs utilized the scrounger strategy, and this strategy was successful. Feral pigs have also been found to use producer and scrounger strategies. Subordinate feral pigs are more likely than dominant pigs to find food sites, which dominant pigs benefit from (Held et al., 2000).

Why do captive pigs exhibit foraging-like behaviors?

Captive domesticated pigs are provided with food and thus do not need to forage. However, they still spend large amounts of their time exhibiting foraging-related behaviors such as rooting, sniffing, biting, and chewing on edible and inedible materials. Often, they are provided with hay so they may carry out these behaviors (Studnitz et al., 2007). When deprived of material suitable for these behaviors, pigs perform stereotypies , which are fixed repetitive actions indicative of boredom or frustration (Grandin, 2009). In pigs, stereotypies may include chewing metal bars on their crates, pacing, and chewing with nothing in their mouths.

The importance of foraging behaviors and the relationship between pig stereotypies and inability to forage are well established. When pigs kept on concrete floors were allowed access to soil outdoors, they immediately began to root (Day et al., 1995). Pigs with nose rings do not root, presumably because the pressure of the ring causes pain when rooting (Bornett, 2003). However, when pigs’ nose rings were removed, they resumed rooting (Studnitz et al., 2003). Pigs prevented from rooting were found to spend approximately the same amount of time performing stereotypies as other pigs spend rooting (Day et al., 1996).

This suggests that biting and chewing non-edible materials and rooting are related to boredom and the desire to explore surroundings. However, stereotypies and foraging behaviors increase when food is depleted, suggesting that some of these behaviors are hunger related.

Day et al. explored the reasons behind these behaviors by offering domestic pigs three tubes to chew. The first tube released water. Because the pigs were given unlimited access to water, chewing on this first tube indicated exploratory behavior. The second tube released a saccharin solution, which tastes sweet but has no nutritional value. The third tube released a sucrose solution, which provided the pigs with a sweet tasting and nutritious drink. Some pigs were put on a low feeding schedule (restricted access to food) while others were put on a high feeding schedule (unrestricted access to food). The researchers’ results are shown in [link] .