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Pig behavior assessments offer clues for housingPig behavior assessments offer clues for housing

Findings will help devise housing that provides pigs with room to roam and protection from more aggressive herd mates.

June 14, 2017

5 Min Read
Pig behavior assessments offer clues for housing
A piglet stands near its mom's ear.Gregory Urquiaga/UC Davis

Is one sow better than another for inclusion in group housing? Piglet No. 3 is not sure what to make of the empty kiddie pool where she finds herself standing at the University of California-Davis (UC-Davis) Swine Research & Teaching Facility. She grunts softly, sniffs at the ribbed-plastic floor and glances at the people watching her explore.

“See how she opens her mouth and sucks in air? Pigs use their strong sense of smell to gather information,” professor Kristina Horback, an animal-cognition expert with the UC-Davis department of animal science, pointed out.

Horback is conducting personality tests with several four-week-old female piglets to identify aggressive and social behaviors, measure their response to human handling and approach, assess their willingness to explore an open field and study their alarm response to a novel object.

Horback has studied animal cognition in several mammal species, including elephants, chimps, prairie dogs, dolphins and whales. At UC-Davis, she is building on her pioneering research examining the role personality plays in the welfare and sustainable production of farm animals like cattle, sheep and swine.

Horback’s research is helping the nation’s pork industry adapt to new legislative and marketplace demands to raise pigs in group housing rather than in individual crates, which have been the norm for the last 40 years.

Thomas Parsons, a University of Pennsylvania veterinary researcher who works with pig farmers across the nation, noted that Horback “is laying the groundwork for answering a fundamental question in the pork industry: Do we have the right animal? Is one pig better than another in a group setting? Or, is there an optimal combination of personalities?”

There are currently more questions than answers in the field of pig personality, but Horback knows one thing for sure: A pig is not a pig is not a pig. “Pigs have distinct personality traits that remain relatively stable throughout their lives,” she said. “They are not going to react to the same stimuli in the same way.”

Designing more peaceful pens

Pigs are hierarchical, and battles for dominance can get bloody. Fifty years ago, pigs were housed in open barns and had to fight for the feed farmers tossed on their floor. Dominant pigs got more, timid pigs got less and some pigs suffered miscarriages in the scramble. To protect pigs and their productivity, the industry switched to gestation stalls: 2 ft. x 7 ft. enclosures that let each sow eat in peace but do not provide enough room for them to turn around.

Prompted by complaints from animal welfare groups, consumers and 70 brand-name retailers like McDonald’s, the pork industry is now transitioning from crates to group pens. Gestation stalls have been banned in the European Union and in 10 U.S. states, including California. Working with Parsons and other colleagues, Horback is helping farmers and pigs adapt to housing that provides room to roam and protection from aggressive kin. Personality research can help.

“For 40 years, swine genetics focused on production traits like weight gain, litter size and disease resistance,” Horback said. “Have we been inadvertently breeding for specific behavior and personality traits? Are some personality traits better than others, not just for the individual but for the group as a whole?”

Farmers prefer pigs that gain a lot of weight, and aggressive piglets often eat more. However, if dominant pigs get fat at the expense of the others, that might not provide a net gain.

Researchers wondered whether social and passive pigs will grow bigger and be more content if aggressive pigs are removed from the group and also whether bold pigs are better equipped to deal with another sow’s aggression, or if a few dominant personalities improve social order.

“Right now, we’re just identifying the differences,” Horback said. “We need to see a lot more numbers before we can confidently say what personality traits, or mixture of traits, work best in a group.”

Personality testing

To assess a person’s personality, psychologists rely on self-reporting surveys like the Myers-Briggs Type Indicator. Since Horback cannot interview the pigs, she puts them in situations that “let them show their true colors.”

Spunky, aggressive piglets squeal when held firmly by humans for one minute. Passive pigs do not squeal as much when handled, perhaps out of resignation. Sociable sows are the first to sniff their fellow pen mates, and they interact more easily with humans — snuffling at their boots and such.

Fearful pigs often freeze when they are isolated in a strange environment, such as the empty kiddie pool where piglet No. 3 is standing at the UC-Davis Swine Facility. Piglet No. 3 is not overly vigilant, not pacing or frozen in place. Horback is also assessing how pigs respond to a novel object — in this case the blue, vibrating Bumble Ball she places in the makeshift pen of piglet No. 3. The toy bounces in unpredictable patterns and can lurch forward without warning, simulating a predator attack.

“I try to make the experiments as ecologically relevant as possible,” Horback said. “It’s not as convincing as casting a stuffed badger into a colony of prairie dogs (as Horback did several years ago while working with professor John Hoogland from the University of Maryland), but it seems to work.”

Piglet No. 3 keeps a close watch on the Bumble Ball before sniffing it and rooting at the floor. “Pigs love to root,” Horback said. “That shows she’s letting her guard down and exploring the environment. She’s coping with the isolation and Bumble Ball quite well.”

In addition to measuring personality traits, Horback will soon start testing piglets for “cognitive bias,” or mood, to see if certain personality traits correlate with “positive affective states,” or optimism. In previous research, Horback has seen evidence of a link between aggressive personalities and a positive mood.

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