Animals Make Us Human: Creating the Best Life for Animals

by Dr. Temple Grandin and Catherine Johnson

Houghton-Mifflin Harcourt, New York, NY, 2009
ISBN 978-0-15101489-7

(In United Kingdom, book title is "Making Animals Happy" and ISBN is: 978-0-7475-9714-8)

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An Excerpt from Chapter 6: Pigs

The Curious Pig: SEEKING – Environmental enrichment to improve farm animal welfare

Pigs have lively, active minds, and they need to live in an enriched environment that lets them stimulate their SEEKING emotion. In my research, the piglets raised in a barren plastic pen were much more hyper than piglets raised on straw. The piglets in the barren pens were also greater stimulus seekers. When I cleaned the pens with a hose, they bit madly at the hose and at the water stream. When I cleaned the feeders, they excitedly bit at my hands. They were starved for stimulation.

Under stimulated pigs will chew off each other’s tails, too. It’s horrible. It might be just one pig that starts it, but once one pig draws blood other pigs can get involved, too. It’s not really aggression; the pigs are just desperate for something to explore and chew. Some pigs bred for lean meat have an especially high SEEKING drive and they will root and chew up a person’s boots. They also do a lot more tail biting.

Pigs have such an intense SEEKING emotion that good stockpeople use pigs’ natural curiosity to move them. Usually, stockpeople think the way to herd pigs out of a pen is to get behind them and drive them forward by pressuring their flight zone. But very often this doesn’t work; they just scatter and pile up because people try to push them too quickly. The best way for a stockperson to move pigs out of a pen is to open the gate and just stand right next to it inside the pen. The most curious pigs will come up to investigate the stockperson. Then, after they’re done investigating the stockperson, they’ll walk out of the pen into the alleyway to investigate it. The second most curious pigs will do the same thing. They’ll walk up to the stockperson to explore him and then walk into the alleyway to explore the alleyway. At some point the herd instinct will kick in and the rest of the herd will follow the leader pigs out of the pen.

There’s another problem with moving pigs, which is that when the pigs are driven they often refuse to walk on an unfamiliar floor surface. I consulted on a farm where piglets that had been raised in pens with plastic floors were impossible to drive down a corridor with a concrete floor. It was utter frustration for the handlers. I suggested opening all the gates and then going out for dinner. When we came back, the pigs were playfully exploring the concrete floor and were now easy to move into the next building. When the piglets were pressured to walk on a concrete floor for the first time, FEAR took over and blocked the urge to SEEK. With the pressure gone, SEEKING overrode FEAR, and the pigs explored the new floor and got used to it.


Pigs are obsessed with straw. When I threw a few flakes of wheat straw into my pen of piglets, they rooted in it at a furious pace. After the straw had been chewed up into tiny short two-inch pieces, they lost interest. The chewed-up straw was now boring and no longer novel.

So far, no one has found anything that can compete with straw for a pig’s interest and attention. One recent study tested seventy four different objects — things like a ball with a bell inside, hanging buckets, pieces of carpet, cloth strips, a metal colander, compost, shredded paper, and sawdust. Lavender straw came in first.

Straw is extremely good for pigs, especially full-length straw. Chopped straw isn’t nearly as satisfying. My straw-bedded pigs were calm. When I cleaned the feeders in their pen, they moved quietly away and there was no hyper biting. One study of tail biting found that pigs needed only a small amount of fresh straw two times a day to keep them from biting each other’s tails. Straw is so important to pigs that in 2001 the European Union passed a Commission Directive stating that “pigs must have permanent access to a sufficient quantity of material to enable proper investigation and manipulation activities, such as straw, hay, wood, sawdust, mushroom compost, peat or a mixture of such, which does not compromise the health of the animals.”

Unfortunately there are two drawbacks to straw. First, we have a limited amount of straw in this country, and we’ll have even less suitable bedding materials if we start using straw and chopped cornstalks to make ethanol. Canada has plenty of straw because it grows so much wheat, but it’s too expensive to ship Canadian straw to American pig farms.

The solution for limited supplies of straw is to use straw exclusively for enrichment, not for bedding. You need a huge amount of straw to make proper straw bedding so that the pigs will stay clean and not be wallowing in manure. I have seen straw-bedded systems where the farmer skimped on straw and it was disgusting, but you don’t need a huge amount of straw to create an enriched environment. All of my pigs were reared on concrete slatted floor pens, and just a small amount of straw made a huge difference in satisfying SEEKING.

The other problem is that in large commercial systems straw clogs up the liquid manure systems because it jams the pumps. This is the reason why most large U.S. farms don’t give their pigs straw for enrichment, which they should all be doing. One way to minimize the cost is to “toilet-train” the pigs. When pigpens are set up right, pigs can have very neat pooping habits. They will poop in cold, wet places near a waterer and avoid messing in dry places where they sleep and eat.

If a farm isn’t willing to give its pigs straw, it should provide other forms of enrichment. Pigs like odorous objects they can chew, “deform” (meaning the object changes shape or size as the pig manipulates it), and destroy. In the l980s, I did one of the first experiments showing that pigs like soft things they can chew up and destroy. I hung three objects on strings above a pen of piglets that didn’t have straw to root in and chew: a rubber hose, cloth strips, and chains. Each object was attached to a switch that activated a counter whenever a pig pulled on it. The rubber hose and the cloth strips received a lot more votes on the counters than the chains.

Stockpeople also need to rotate the objects they give the pigs. One study says you probably need to rotate toys in and out as often as every two days. My pigs were much more interested in rooting and chewing the new objects I brought each day compared to the objects I had brought just the day before. The instant I dropped an old telephone book into the pen they ripped it to shreds. Then, after they’d frilly rooted through all the ripped-up pages, they lost interest in it. Pigs need new things to explore because novelty turns on SEEKING. A pig can’t keep exploring the same thing over and over again.

The other approach to satisfying the SEEKING emotion that I like is announced rewards. Instead of just giving the pigs their straw a couple of times a day, you use a conditioned signal to alert them to the fact that the straw is coming. That puts the pigs into the looking-forward-to state all animals and people love. There have been two studies of announced rewards or enrichments that I know of. Both found that an announced reward or enrichment made the animals act happier. One study looked at two groups of piglets that were stressed out because they were being weaned. In the experimental group, the pigs heard a doorbell just before a door opened up and let them into a hallway covered with straw and mixed seeds. That turned the doorbell into a conditioned stimulus, like the bell for Pavlov’s dogs or the clicker in clicker training. The control group pigs were given the straw and seeds with no announcement. The “anticipation” pigs played more and fought less after they were weaned than the control pigs.

Why is it so fascinating for pigs to chew up straw until it is in tiny shreds? I think the pigs motivation is similar to mine in my childhood days when I spent hours dribbling sand through my hands. As each tiny sand grain flowed through my finders, I scrutinized how the light reflected off of it. Each particle had a different shape, and the sparkling reflections changed as I varied the flow through my fingers. I think this may be true for pigs because they are so intensely focused on the things they manipulate with their noses. Each little flake of straw is different and fascinating, and the pigs are driven to explore and chew their straw until it’s all gone. Both pigs and children with autism are obsessed with the things they like to manipulate.

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