There remains some uncertainty regarding the roles of internal and external factors in the organization of feeding behaviour. In the pig (Sus scrofa) there are important scientific and welfare-related reasons for determining the extent to which feeding behaviour is largely pre-programmed or, alternatively, responsive to the environment. To examine the sensitivity of feeding behaviour in the pig to external stimuli the effect of food reward frequency and size on the post-feeding behaviour of sows was tested in three experiments in a sand-filled test arena. In Experiment 1a, five treatment and five control sows were observed for 45 min day-1 , 5 days a week for 3 weeks. In the second week a single food pellet preceded by a buzzer was presented three times during a test period for treatment sows. The sows initially responded by searching after the discovery of the pellet, but this response declined with time (mean no. of bouts: 11.6, 15.8, 16.4, 10.2, and 6.4 for Days 1-5, respectively; P < 0.01). All ten sows searched for 16 food pellets buried in the sand in Experiment 1b, and they responded to the declining encounter rate by decreasing searching behaviour. In Experiment 2 nine sows were observed for 35 min-1 day-1 for 18 days and were given zero, three pellets or 1 kg of pellets in a Latin square design which was replicated twice. The searching response increased with reward size (mean proportion of observed time: 0.005, 0.017 and 0.038 for reward sizes 1-3, respectively; P < 0.001), but had declined by the second reward (mean proportion of observed time: 0.027 and 0.013 for Replicates 1 and 2, respectively; P < 0.01). It was concluded that although the ingestion of food in the pig may initially result in short-term positive feedback effects on feeding motivation, this response is strongly modifiable by experience. As there was little evidence that sows enter a 'preprogrammed' loop of feeding behaviour, processes other than those normally associated with foraging must be used to explain the occurrence of persistent oral behaviour shown in intensively farmed pigs.
- Foraging behaviour