Why do animals yawn? Why do cats eat grass? Why do they purr? And why on Earth does my pet eat poop? Benjamin Hart, DVM, PhD, DACVB, and distinguished professor emeritus at the University of California – Davis, addressed some of the more inexplicable behaviors of companion animals in his talk at the American Veterinary Medical Association’s (AVMA) conference this year: “Why do they do that? Purring, yawning, flipping out on catnip, and eating poop.”
Why do cats eat grass?
Hart cited statistics that said about 80% of cats eat plants of some kind or another. It is commonly thought that grass eating in cats is linked to intestinal distress. However, in a web-based study of more than 2,500 cat owners, Hart said only 5% of plant-eating cats showed signs of illness, although 32% vomited after eating grass. About half of the cats in the survey ate mostly grass as opposed to other plants.
The results were much different for younger cats (less than 1 year old). Among these cats, only 1% to 2% showed signs of illness, and only 2% vomited after eating grass or plants. Also, about 80% of young cats ate plants other than grass.
Hart concluded that grass eating among cats is normal and may have some ongoing health-related effects, such as expulsion of intestinal worms. However, a sudden increase in grass-eating behavior could signal intestinal distress, he said, so the behavior should be monitored.
Why do cats purr?
The sound of a purring cat is music to many cat owners’ ears. But the fact is that no one really knows why this behavior occurs. Lions and tigers and other roaring species cannot purr, and purring species like domestic cats, cheetahs, jaguars and bobcats cannot roar. Roaring and purring probably serve different evolutionary purposes, Hart said.
Cats purr when they seem to be happy, but also when they are sick, injured or even giving birth. Some of the latest theories say that purring is a way to repair muscles and tendons after a vigorous chase. Hart cited research that said purring occurs in the range of 25 Hz, which is identical to the frequency that promotes healing of wounds and tissue. Inactive cats that lie around on the couch all day may also purr in order to keep up their muscle mass.
Why do animals yawn?
Hart said that although the common belief is that yawning expands the lungs and oxygenates the brain, many animals yawn without low oxygen levels.
The current leading hypothesis is that yawning cools the brain, Hart said. During inactivity, cerebral circulation slows and the brain warms up. Yawning cools arterial blood via the nasal countercurrent veins, and thus cools off the brain, allowing it to function better.
The contagious nature of yawning could also be explained with this theory. If one member of a group yawns, it signals the others that action is imminent so the others need to cool their brains as well. A recent study found that yawns are contagious between humans and dogs. Hart speculates that coevolution between dog and man has led to this phenomenon.
Why does my dog eat poop?
Coprophagia has grossed out and confounded many pet owners and veterinarians for a long time. Unfortunately, there does not seem to be an effective way to stop dogs from eating their poop, although Hart did offer some interesting statistics on the topic.
He cited a recent, unpublished study that included information from nearly 1,500 pet owners with dogs that had been seen eating feces daily or weekly at least 10 times. According to the survey, the top five feces-eating dog breeds were the Labrador retriever (10.4%), golden retriever (5.8%), Basset hound (5.5%), German shepherd (5.3%) and Shetland sheepdog (4.7%).
About 10% of the dogs ate only their own stool, whereas 32% ate the feces of others, and nearly half of all dogs who ate feces didn’t care who it belonged to. “Most dogs ate any ol’ stool,” Hart said.
Other findings included:
- Female dogs were more likely than male dogs to engage in this behavior (60% vs. 40%).
- The behavior does not reflect poor den sanitation: 82% of dogs in the survey almost never soiled their own house.
- Almost all dogs opted for fresh feces as opposed to aged feces.
- Neither behavior modification techniques nor food additives seemed to be effective in changing the behavior.