Dietary modification of behaviour in pigs
Résumé
Put simply, with pig nutrition management, we aim to maximize output for minimal input, both in terms of litter size and subsequent pig growth rate. Food is the most important resource for pigs, and pigs will use aggression to gain or protect food. Naturally, pigs are designed to have gradual exposure to solid feed and wean late, and eat numerous meals over the course of the day, of variable quality, spending a high proportion of activity in foraging behavior. Under many commercial conditions, pigs have abrupt exposure to solid feed and wean early, eat fewer, high quality meals and spend little time foraging. Feeding system design for pigs housed in groups will impact not only aggression but also other aspects of behavior. Feeding system design incorporates not only the feed delivery system, but also the food composition, which in turn may comprise of physical form, flavor and ingredients, the last of which will be the focus of this presentation. The impact of ingredients on behavior may be intentional and unintentional. For example, increasing tryptophan in the diet can influence serotonin concentrations and intentionally reduce aggression when pigs are mixed. Similar behavioral effects can be seen with increasing resistant starch in the diet. However, adding the beta-agonist ractopamine to the diet for known production benefits, can also unintentionally increase aggressiveness, reactivity to handling and hyperactivity. More recently, we have been examining the proposed gut-brain axis, whereby the gut microbiota communicates with the CNS – possibly through neural, endocrine and immune pathways – and thereby influencing brain function and behavior. There is also a suggested role for the gut microbiota in the regulation of anxiety, mood, cognition
and pain. Recent studies examining alternatives to antimicrobials, such as amino-acids and probiotics, delivered as short- to medium-term supplementation, can affect behavioral and welfare responses to stressors and impact gastrointestinal microbial populations. L-glutamine appeared to confer similar benefits to, and thus could be a viable alternative to dietary antibiotics. A synbiotic supplement of Lactobacillus + fructo-oligosaccharide + Saccharomyces cerevisiae cell wall may confer memory advantages in 3 cognitive tasks, regardless of the nature of the reward and the memory request. Feeding a probiotic supplement to the sow prior to farrowing
has shown indirect short- and longer-term behavioral effects on piglets, demonstrating the existence of a sow-piglet axis. The existence of a gut-brain axis offers a potential mechanism by which we can develop dietary therapeutic strategies to help pigs cope with stressful events, and potentially alter affective states both ameliorating the negative and enhancing the positive.