Description
Features |
Length of arena: 5.7m |
Width of arena: 12m |
Height of ‘X’ acrylic boards: 60cm |
Introduction
The Pig Foraging Arena is designed to study foraging behaviors in pigs, who are social foragers often learning about feeding sites from their family groups (Figueroa, Solà-Oriol, Manteca, & Pérez, 2013; Oostindjer et al., 2011). Additionally, pigs establish dominance hierarchies within their groups, significantly affecting both their individual foraging decisions and the behaviors of their peers (Held et al., 2010). The arena itself is a spacious Open-Field Arena equipped with X-shaped mounts that hold reward buckets around its perimeter. Social behaviors are frequently evaluated using the informed forager paradigm, where a trained pig familiar with the reward buckets is tested alongside an untrained pig.
Beyond studying socially influenced foraging behaviors, the Pig Foraging Arena can be used to assess spatial navigation and memory in pigs. The flexibility of the setup allows for varying the number and arrangement of reward buckets to adjust the difficulty of the tasks. The buckets are equipped with wire mesh covers to separate the pig feed inside from the food bait on top, thereby minimizing the influence of olfactory cues.
The spaciousness of the arena and the use of appetitive rewards help reduce stress for the subjects during training and testing. The Pig Foraging Arena can also be adapted for different experimental protocols, such as preference testing. Other apparatus used to evaluate pig behaviors include the Pig T-maze, the Piglet Removable Y-Maze, the Pig 8 Arm Radial Maze, the Pig Open Field, and the Pig Hebb-Williams Maze.
Apparatus and Equipment
The Pig Foraging Arena features a testing area measuring 5.7 x 12 meters, with walls made of galvanized metal sheets. A start box connects the arena to the pen room via a corridor, separated from the main arena by a manually operated flap. The floor of the arena is marked with a 1 x 1 meter grid. Along the perimeter of the arena are four X-shaped mounts, each constructed from boards that are 60 cm high. Each mount is designed to hold a bucket in each corner, with each bucket covered by a removable wire mesh cover where food bait can be placed. The arena includes four gates, positioned on its sides, for exit.
Training Protocol
Clean the arena after every trial. Appropriately light the arena. A tracking and recording system such as the Noldus Ethovision XT can be used to assist with observations.
Below is a sample protocol for assessing the social influences on foraging behaviors in informed and non-informed pairs. This protocol utilizes eight reward buckets, with each mount holding two buckets placed at the distal corners.
Place bait in four of the buckets within the arena. Introduce pairs of subjects to the foraging arena, allowing them to familiarize themselves with the environment and consume the food reward. Repeat this process the next day. On the subsequent day, bait only two buckets and allow the subjects to explore the arena individually. Conclude each trial by removing the subject once all the food has been consumed or after 10 minutes have elapsed.
The goal of training trials is to establish subjects as either informed or non-informed foragers. For the informed forager, conduct both search and relocation trials, while for the non-informed forager, conduct only search trials. Each day, perform two training trials with a one-hour inter-trial interval. Continue this process until the informed pig meets the learning criterion.
Search Trial
Bait one of the eight buckets with food. Take the subject from its home pen and guide it to the start box. Release the subject from the start box to explore the arena. Once the subject finds and consumes the food, remove it from the arena and return it to the start box to begin the relocation trial for the informed forager. For the non-informed forager, return it directly to its home pen.
Relocation Trial
Wipe the previously baited bucket and bait the same bucket again. Release the subject from the start box and allow it to explore the arena. Lead the subject out of the arena after it finds and eats the food bait.
Testing Trials Search Trial
Bait one of the buckets in the arena. Remove an informed forager from its home pen and lead it to the start box. Release the subject from the start box and allow it to explore the arena. Lead the subject out of the arena after it finds and eats the food bait.
Literature Review
Investigation of foraging behavior in pigs when accompanied with another forager
Held et al. (2010) explored the foraging strategies used by subordinate pigs in the presence of different types of dominant co-foragers. They divided thirty juvenile Large White × Landrace pigs into groups of six, with each group containing two light subordinates (30 kg) and four heavier dominants (40 kg). These pigs were tested in the Pig Foraging Arena, featuring 12 buckets positioned in the distal corners of four X-mounts. Two buckets were baited: one with a large amount of food and the other with a small amount. The subordinate pigs received informed forager training, while the dominant pigs only participated in search trials. The dominants were split into two groups: non-informed (NI) and non-follower (NF). For NI dominants, a different bucket was baited in each trial, whereas the same bucket was consistently baited for NF pigs.
During the testing phase, subordinates performed search trials first, then paired with either an NI or NF dominant for their relocation trial. The results showed that in the I-NI tests, informed (I) pigs had no significant preference for retrieving either bait first. However, in the I-NF tests, I-pigs tended to retrieve the larger bait first. The order in which the I-pigs visited the baits did not affect the total time spent at the baits or feeding. Additional observations revealed that during I-NI tests, the dominants often displaced the I-pigs from one or both buckets. In contrast, during I-NF tests, I-pigs were never displaced from the baited buckets, and NF dominants did not follow or attempt to steal the bait.
Investigation of value-based discrimination of food sites by pigs
Held, Baumgartner, KilBride, Byrne, and Mendl (2005) assessed the spatial memory capabilities of nine juvenile female Large White × Landrace pigs using the Pig Foraging Arena. The setup involved eight buckets positioned at the distal corners of the X-mount, with two of these buckets baited—one with a large amount of food and the other with a smaller amount, accompanied by a brick as an obstacle. The study was divided into two experiments. In the first, the pigs were allowed to retrieve both baits during their relocation visit. In the second, they were restricted to retrieving only one of the two baits.
The results from the first experiment showed that pigs visited more buckets during search trials than during relocation trials, and all pigs successfully located the two baited buckets. There was no significant preference for retrieving either bait first. However, in the second experiment, the pigs showed a clear preference for retrieving the larger bait first. Further control trials involved four pigs, where bricks were placed in both the large and small bait buckets, and the pigs were again restricted to choosing only one bucket during relocation. The subjects continued to prefer the bucket with the larger bait.
Investigation of foraging strategies of pigs subjected to exploitation
Held, Mendl, Devereux, and Byrne (2002) investigated the impact of exploitation by dominant co-foragers on the foraging behaviors of pigs using the Pig Foraging Arena. This task involved eight buckets positioned at the distal corners of the X-mounts, with one bucket baited. Sixteen juvenile female pigs (Sus scrofa) were housed in pairs, each consisting of a light-weight subordinate and a heavy dominant pig. The subordinates received informed forager training (I-pigs), while the dominant pigs (Non-informed pig, NI-pigs) were trained only through search trials. After completing the training, the pairs of I-pigs and NI-pigs were tested together in joint foraging trials. The results showed that in 570 instances, I-pigs altered their direction of movement when NI-pigs closely followed them. It was also noted that I-pigs were more likely to approach the baited bucket when the NI-pigs were out of sight, further away, or not in close proximity.
Investigation of the effects of social dynamics on foraging tactics of pigs
Held, Mendl, Devereux, and Byrne (2000) examined the social tactics pigs use in foraging through an informed forager paradigm within the Pig Foraging Arena. Sixteen juvenile female pigs, a crossbreed of Large White, Landrace, and Duroc, were categorized into two weight-based groups: eight ‘light’ pigs (mean weight ± SD = 29.87 ± 2.29 kg) and eight ‘heavy’ pigs (mean weight ± SD = 40.62 ± 2.13 kg). The experiment involved eight buckets placed at the corners of X-mounts, with one bucket baited. During training, a pig from the light group performed both search and relocation trials, earning the designation of informed pig (I-pig). The I-pigs were observed to search more buckets during the search trials compared to the relocation trials. Pigs from the heavy group, trained only through search trials, were labeled non-informed pigs (NI-pigs). In the testing phase, each I-pig explored the arena alone before foraging jointly with an NI-pig. The foraging behaviors of the NI-pigs indicated that they followed the I-pigs to the baited buckets during joint trials, rather than investigating the buckets randomly as they did during training search trials. At least six of the eight NI-pigs exploited their I-pig partners by displacing them from the food bucket to consume the bait themselves.
Data Analysis
The following can be observed using the Pig Foraging Arena:
- Total number of bucket investigated prior to the baited bucket
- Total number of buckets visited
- Total number of buckets revisited
- Time spent feeding
- Order of baits received (for trials with more than one baited bucket)
- Number of errors
- Time taken to complete a trial
Strengths and Limitations
The Pig Foraging Arena provides flexibility in arranging bucket placements and adjusting their numbers, enabling the investigation of spatial navigation and memory abilities in pigs. Its spacious design accommodates multiple subjects simultaneously, facilitating the assessment of social dynamics affecting behaviors such as foraging. Moreover, the arena can be customized for various experimental protocols, including studies on preference behaviors. The buckets are equipped with mesh covers that allow the placement of feed or substances underneath, thereby minimizing olfactory cues and supporting experiments where access to rewards needs to be controlled. With four exit points, the arena allows quick removal of subjects, which is beneficial for experiments requiring strict reward choice restrictions.
The subject’s exploratory motivation plays a crucial role in task completion. When testing subordinate and dominant pairs, the dominant group’s presence could potentially disrupt the subordinate’s task performance due to stress. Moreover, task performance might be influenced by residual odor trails from prior trials or unintended stimuli in the environment. Variables such as age, gender, or strain of the subjects could also impact their performance in the task.
Summary
- The Pig Foraging Arena is used in the assessment of foraging behaviors and cognitive abilities of pigs.
- The arena consists of 4 X-shaped mounts placed along the arena’s periphery that have provisions for placement of 4 buckets each.
- Each bucket contains a wire mesh cover useful in using odor masks or restricting access to rewards.
References
- Figueroa, J., Solà-Oriol, D., Manteca, X., & Pérez, J. F. (2013). Social learning of feeding behaviour in pigs: effects of neophobia and familiarity with the demonstrator conspecific. Applied Animal Behaviour Science, 148(1-2), 120-127. doi:10.1016/j.applanim.2013.06.002
- Held, S., Baumgartner, J., KilBride, A., Byrne, R. W., & Mendl, M. (2005). Foraging behaviour in domestic pigs (Sus scrofa): remembering and prioritizing food sites of different value. Animal Cognition, 8(2), 114-121. doi:10.1007/s10071-004-0242-y
- Held, S., Mendl, M., Devereux, C., & Byrne, R. W. (2000). Social tactics of pigs in a competitive foraging task: the ‘informed forager’ paradigm. Animal Behaviour, 59(3), 569-576. doi:10.1006/anbe.1999.1322
- Held, S., Mendl, M., Devereux, C., & Byrne, R. W. (2002). Foraging pigs alter their behaviour in response to exploitation. Animal Behaviour, 64(2), 157-165.
- Held, S. D., Byrne, R. W., Jones, S., Murphy, E., Friel, M., & Mendl, M. T. (2010). Domestic pigs, Sus scrofa, adjust their foraging behaviour to whom they are foraging with. Animal Behaviour, 79(4), 857-862. doi:10.1016/j.anbehav.2009.12.035
- Oostindjer, M., Bolhuis, J. E., Mendl, M., Held, S., van den Brand, H., & Kemp, B. (2011). Learning how to eat like a pig: effectiveness of mechanisms for vertical social learning in piglets. Animal behaviour, 82(3), 503-511. doi:10.1016/j.anbehav.2011.05.031