Social learning of feeding behaviour in pigs: Effects of neophobia and familiarity with the demonstrator conspecific

Abstract

Social interactions facilitate animals learning of new features of their environment minimizing a trial and error process. It has been observed in some species that food cues can be acquired by one individual (the observer) from an animal model (demonstrator) due to social learning. Three experiments were performed to evaluate whether weaned piglets may show a preference for a flavoured feed following brief social interactions (30 min) with an experienced demonstrator. After the social interaction between demonstrator and observer pigs, a 30-min choice test between the flavoured feed previously eaten by demonstrators (DEM-feed) and other flavoured feed (OTH-feed; Exp. 1 and 2) or a known unflavoured starter diet (Exp. 3) was performed with observer animals. Greater intake of DEM-feed occurred when demonstrators and observers were from the same pen (Exp. 1) or from the same litter (Exp. 2), but not when observers and demonstrators were unfamiliar with each other (Exp. 1). Observers also preferred flavours previously eaten by the demonstrator over their unflavoured diet already known. Social interactions with a conspecific pig that had a recent experience with a flavoured feed enhanced the preference for that feed and could even override neophobia to a new feed. The familiarity of conspecific demonstrators plays a key role in social learning of new feed cues probably due to selective exploration involving closer snout-to-snout contacts with kin conspecifics.

Introduction

Food preferences and aversions are strongly influenced by individual learning experience (Dwyer et al., 2009, Sclafani, 2004, Sclafani and Zukerman, 2009) but also are determined by social interactions (Galef and Whiskin, 1997, Galef and Whiskin, 2001). In natural environments, social learning increases the probability of survival, especially in young individuals that benefit from learning behaviours from experienced animals (Galef and Giraldeau, 2001, Thornton and Malapert, 2009). It has been reported in several species that food information can be transferred from one individual to another through social learning (Oostindjer et al., 2011, swine; Posadas-Andrews and Roper, 1983, rats; Provenza and Balph, 1987, ruminants). In rats, when a conspecific (demonstrator) ate a new flavoured food, another rat (observer) learnt to prefer that food in a future exposure after a brief interaction with this experienced animal because of the contact with food odours in the breath of the demonstrator rat. This learning is not affected by the age or familiarity of the demonstrator and even appeared when such an act led to inferior benefits (Galef, 1996, Galef and Whiskin, 2008a). However, a common observation in the social learning literature is that individuals often copy kin with the expectation of obtaining the same rewards (Coussi-Korbel and Fragaszy, 1995, Laland, 2004). Evolutionary theory indicates that familiar animals also share a common environment and probably they are genetically related (Laland, 2004, Valsecchi et al., 1996), which make social learning an adaptive behaviour (Laland, 2004).

Pigs are highly social animals and begin to form social relationships with littermates within hours of birth (Graves, 1984). Nevertheless, there have been only a few studies of social learning of feeding behaviour in pigs. Nicol and Pope (1994) and Held et al. (2000) showed that an inexperienced pig could follow an experienced pig and learn about the location of food, and Morgan et al. (2001) also demonstrated that feed intake is enhanced when an inexperienced pig is housed with an experienced conspecific. However, a “follow the leader” can be a local enhancement phenomenon in which the observer animal is attracted to the place that demonstrator visits.

At weaning, piglets face three main challenges in the intensive pig-farming industry, including changes in the physical environment, the psychological stress that accompanies moving and mixing animals, and a major change in feed composition. Early weaned piglets have to find their own feed, which it is more bulky and dry (usually >88% of dry matter), less digestible than milk, and composed of ingredients that piglets have not previously encountered. In these conditions most weaned piglets are reluctant to eat the new feed, leading to anorexia on the first days after weaning (Fraser, 1984, Moeser et al., 2012, Pluske et al., 2007). Neophobic avoidance of new feeds may seem a maladaptive process for omnivorous species that need to consume a varied diet to obtain adequate nutrition and may become critical in intensive production systems where new diets have to be incorporated during a short period of time (Provenza and Balph, 1988). However, neophobia may be reduced through a learning process before or after birth involving contact with flavour cues and associations between those components and positive consequences (Ackroff and Sclafani, 2010, Hepper and Wells, 2006, Mennella et al., 2001, Oostindjer et al., 2009, Oostindjer et al., 2010).

Social interactions with experienced pigs could help naïve pigs to learn about environment conditions with minimal trial and error. Through social learning, individuals do not need to search their entire home range, or sample potentially toxic foods (Laland, 2004). The aim of this study, composed of three experiments, was to investigate if social learning in pigs could help to establish preferences towards a particular ingredient or flavour after interacting with a conspecific that has eaten these compounds. In the first experiment we hypothesized that pigs can learn to prefer a flavoured feed following brief interactions with conspecifics during the post-weaning period, without participating or watching during the demonstrator feed intake. We also hypothesized that this learning could be affected by the familiarity of the demonstrator. In a second experiment, we established whether these preferences were affected by the type of familiarity (penmates vs. littermates) and finally in the third experiment we studied if social learning could increase preferences for a diet over the previously known unflavoured feed.

Experiments were conducted at the weanling unit of the pig facilities belonging to the Universitat Autònoma de Barcelona (UAB). Experimental procedures were approved by Ethical Committee on Animal Experimentation of the UAB. (CEAAH 1406).