Journal Scan: Mans best friend the mini pig?

New Africa/stock.adobe.comWhy they did it

Several domesticated and nondomesticated animals, including cats, horses, seals and monkeys, demonstrate the ability to communicate with people.1 Yet there are differences between domesticated and wild animals in the extent and manifestation of interspecific communication skills in the human environment, suggesting that the process of domestication has shaped these skills.2

The popularity of miniature pigs as pets is burgeoning, likely due to their small size, intelligence and sociability.3 When kept as companion animals, mini pigs occupy a similar niche in the home as dogs. But the process of canine domestication began thousands of years earlier than that of swine,4,5 and these differing trajectories may affect their respective capacities and styles of interaction with humans.

This is the first known study to investigate the interspecific (animal-human) social skills of socialized miniature pigs and compare them with those of family dogs.6

What they did

Ethology researchers at Eötvös Loránd University in Budapest, Hungary, recruited young pigs and young dogs living with families that were exposed to similar social contact with people from the age of approximately 8 weeks.

Two studies were performed, each incorporating food as a motivator. Study 1 evaluated and compared pigs' and dogs' initiative and style in communicating with people, using food as an incentive. Ten pigs (Minnesota and mixed miniature variants) and 10 dogs (of eight different breeds) were enrolled in this this study. The subjects were about 4 months old and divided almost evenly gender-wise; all animals except for the male pigs were intact.

First, each animal was brought into a test room for a videotaped session in which the owner was present but not involved. A control phase consisted of a 60-second pretest, during which the experimenter imitated the action of taking a food treat out of an elevated bowl and placing it on the floor in front of the subject while calling the subject's name. In the test portion of the control phase, the experimenter hid her hands behind her back and remained passive for 120 seconds while staring at the animal in an attempt to establish eye contact. The following food phase was identical to the control phase, but rather than simply imitating the delivery of treats during the pretest portion, the experimenter actually delivered valued treats (sausage for dogs and dog kibble for pigs) to the subjects.

The video was analyzed later for the following behaviors during the 120-second test portion:

Body orientation (duration): Subject comes within 30 cm of experimenter and orients its head toward any part(s) of her body without touching her.

Body touch (frequency): Subject establishes physical contact (e.g. nosing, pawing) with experimenter but does not orient its head toward her.

Face orientation (frequency): Subject comes within 30 cm of experimenter and orients its head toward her face.

Orientation to experimenter (duration): Subject comes within 30 cm of experimenter, orients its head toward her and touches her with some body part.

Vocalization (duration): Subject is vocalizing.

Experimenter-oriented vocalization (duration): Subject vocalizes while orienting its head toward experimenter.

In study 2, the researchers explored receptivity to human pointing gestures in a two-way choice model using different pointing gestures. The researchers tested the same group of pigs (less one; n = 9), but a different group of dogs (n = 9; seven different breeds, two mixes).

Each subject's motivation to eat the food treat was first confirmed by showing the treat to the pet and then allowing the pet to approach and eat it. In the test phase, the experimenter was positioned 2.8 m from the restrained subject. The experimenter placed a food treat in one of two food containers, switched the food containers back and forth to confuse the subject about which container held the treat, and then placed both containers on the floor in front of her. The experimenter then made an attention-getting gesture (clapping sound) while attempting to establish eye contact with the subject, and indicated which container held the treat using a pointing gesture.

Two types of pointing gestures were used in succession: In the distal dynamic sustained (DDS) condition, the experimenter pointed with one extended arm toward the baited container while looking at the subject until the subject made its choice. In the distal momentary (DM) condition, the pointing lasted for only 1 second, after which the experimenter pulled her hand back to her chest and continued to stare at the subject. In both conditions, the distance between the tip of the experimenter's index finger and the container was approximately 70 cm. The subjects were presented with 28 trials in all, 14 per condition.

The videotaped sessions were then evaluated, and the number of correct choices was calculated for each subject per condition; corrections were made for any bias a subject might have toward one particular side.

What they found

In study 1, both pigs and dogs touched and looked at the experimenter more frequently in the food condition than in the control condition. Both species gazed more frequently at the experimenter's face in the food than the control condition, but in the control condition dogs exhibited face orientation to a greater degree than did pigs. Whereas the pigs body-oriented toward the experimenter more frequently in the food condition than in the control condition, the dogs' orientation did not differ between the two conditions. For pigs, vocalization did not differ between the food and control conditions.  

This study revealed similarities between pigs and dogs in their body positioning near, and physical contact with, a person in the absence of food rewards. In the presence of food, touching and face-gazing intensified for both species. Pigs displayed less face orientation than did dogs, and did so almost exclusively in the food condition.

In study 2, dogs performed, on average, above chance in the DDS condition but not in the DM condition. Pigs did not perform significantly above chance in either condition. Furthermore, all pigs and less than half of the dogs displayed lateralized behavior (side bias).

What it means

This study is the first to present similarities and differences between pigs' and dogs' actual behaviors while interacting with people. The presence of food elicited attention-getting behaviors in both species but had a greater impact on the pigs' than the dogs' behavior, suggesting that the former is the more food-motivated of the two. The study shows an important difference between the two species in their willingness to orient toward the human face; the authors explained this variation as being rooted primarily in selection pressure differences in domestication, during which dogs, rather than pigs, were bred to work in close collaboration with people. The authors concluded that dogs and pigs have similar cognitive ability to follow human social cues but differ slightly in their display of specific signals. Further, dogs have a greater natural predisposition than pigs to respond to human stimuli.  

References

1. Miklosi Á, Soproni K. A comparative analysis of animals' understanding of the human pointing gesture. Anim Cogn 2006;9(2):81-93.

2. Miklósi Á, Kubinyi E, Topál J, et al. A simple reason for a big difference: wolves do not look back at humans, but dogs do. Current Biology 2003;13(9):763-766.

3. Marino L, Colvin CM. Thinking pigs: a comparative review of cognition, emotion, and personality in Sus domesticus. Int J Comp Psychol 2015;28(1):23859.

4. Groenen MAM, Archibald AL, Uenishi H, et al. Analyses of pig genomes provide insight into porcine demography and evolution. Nature 2012;491(7424):393-398.

5. Thalmann O, Shapiro B, Cui P, et al. Complete mitochondrial genomes of ancient canids suggest a European origin of domestic dogs. Science 2013;342(6160):871-874.

6. Gerencsér L, Pérez Fraga P, Lovas M, et al. Comparing interspecific socio-communicative skills of socialized juvenile dogs and miniature pigs. Anim Cogn 2019:917-929.

Joan Capuzzi, VMD, is a small animal veterinarian and journalist based in the Philadelphia area.