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Weighing Pig Personality

Is One Sow Better Than Another in Group Housing?

Quick Summary

  • Pigs have distinct personality traits that persist throughout their lives
  • Research is assisting the pork industry as it adapts to new legislative and marketplace demands for group housing
  • Findings will help devise housing that provides pigs with room to roam and protection from more aggressive herd mates

Piglet #3 is not sure what to make of the empty kiddie pool where she finds herself standing at the 嘿嘿视频 Swine Research and Teaching Facility. She grunts softly, sniffs at the ribbed-plastic floor, and glances at the humans watching her explore.

鈥淪ee how she opens her mouth and sucks in air?鈥 asks Professor Kristina Horback, an animal-cognition expert with the Department of Animal Science. 鈥淧igs use their strong sense of smell to gather information.鈥

Woman with shoulder length hair wearing blue blouse
Animal science professor Kristina Horback (Gregory Urquiaga/嘿嘿视频)

Horback is conducting personality tests with several 4-week-old female piglets, identifying aggressive and social behaviors, measuring response to human handling and approach, assessing willingness to explore an open field, and studying alarm response to a novel object. Horback has studied animal cognition in several mammal species, including elephants, chimps, prairie dogs, dolphins and whales. At 嘿嘿视频, 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鈥檚 research is helping the nation鈥檚 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.

鈥淭ina is laying the groundwork for answering a fundamental question in the pork industry: Do we have the right animal?鈥 said Thomas Parsons, a veterinarian researcher at the University of Pennsylvania who works with pig farmers across the nation. 鈥淚s one pig better than another in a group setting? Or, is there an optimal combination of personalities?鈥

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.

鈥淧igs have distinct personality traits that remain relatively stable throughout their lives,鈥 Horback says. 鈥淭hey are not going to react to the same stimuli in the same way.鈥

First up: 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 鈥済estation stalls,鈥 which are 2-by-7-foot 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鈥檚, 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.

鈥淔or 40 years, swine genetics has focused on production traits like weight gain, litter size and disease resistance,鈥 Horback says. 鈥淗ave 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?鈥

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

White pig with mouth open stands by white sow's ear
A piglet stands near its mom's ear.  (Gregory Urquiaga/嘿嘿视频)

If you remove aggressive pigs from the group, will social and passive pigs grow bigger and be more content? Researchers also wonder whether bold pigs are better equipped to deal with another sow鈥檚 aggression, or if a few dominant personalities improve social order.

鈥淩ight now, we鈥檙e just identifying the differences,鈥 Horback says. 鈥淲e need to see a lot more numbers before we can confidently say what personality traits, or mixture of traits, work best in a group.鈥

Stuffed badgers and Bumble Balls     

To assess a person鈥檚 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 鈥渓et them show their true colors.鈥

Spunky, aggressive piglets squeal (loudly!) 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 鈥 snuffling at their boots and such.

Fearful pigs often freeze when they are isolated in a strange environment, which takes us back to the empty kiddie pool where piglet #3 is standing at the 嘿嘿视频 Swine Facility. Piglet #3 is not overly vigilant 鈥 not pacing or frozen in place. Horback is also assessing how pigs respond to a novel object 鈥 in this case the blue, vibrating Bumble Ball she places in piglet #3鈥檚 makeshift pen. The toy bounces in unpredictable patterns and can lurch forward without warning, simulating a predatory attack.

鈥淚 try to make the experiments as ecologically relevant as possible,鈥 Horback says. 鈥淚t鈥檚 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.鈥

Piglet #3 keeps a close watch on the Bumble Ball before sniffing it and rooting at the floor.

鈥淧igs love to root,鈥 Horback says. 鈥淭hat shows she鈥檚 letting her guard down and exploring the environment. She鈥檚 coping with the isolation and Bumble Ball quite well!鈥

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

鈥淎re mean pigs happier?鈥 she asks. 鈥淲e don鈥檛 know yet, but we鈥檙e keeping an open mind. And checking our primate bias at the door.鈥

Media Resources

Kristina Horback, 嘿嘿视频 Animal Science, 510-846-9037, kmhorback@ucdavis.edu

Diane Nelson, 嘿嘿视频 College of Agricultural and Environmental Sciences, 530-752-1969, denelson@ucdavis.edu

Pat Bailey, 嘿嘿视频 News and Media Relations, 530-219-9640, pjbailey@ucdavis.edu

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