Why do they do that? Eating grass, predicting earthquakes, purring, getting sick and more (Proceedings)

Family veterinarians are expected to be all-around authorities on dogs and cats from the standpoint of physiology, pathophysiology, problem behaviors and even interesting tidbits of canine and feline behavior. In the area of feline and canine behavioral trivia, but of considerable interest to pet owners, are a number of topics. Just having something to say about these topics may contribute to your image as a "cool," or at least "with-it" veterinarian. Examples of such topics are:

1. Why does my dog eat grass? Why does my cat, a dedicated carnivore eat grass? Is it because he feels ill and it will make him vomit and get better?

2. I've heard that many times just prior to big earthquakes, dogs, cats and other animals seem to sense that something bad is impending. Can they really predict earthquakes?

3. What is it about an animal being sick? Why don't they want food when they really need it? Why are they depressed when I'm trying to help?

These are some topics that we will briefly touch upon, giving you a bit of information to pass on at a party or wedding reception. Then again, your client may simply ask you a question like this in the exam room and you want to reveal that your depth of knowledge of animal physiology and behavior.

Eating Grass

Both dogs and cats are frequently observed to eat grass and other plant items that presumably have no nutritional value. There is very little in the veterinary literature about this topic, and what there is, points to the animal's feeling ill and the behavior of grass eating induces them to vomit. However, if you have seen dogs or cats eat grass yourself, it is likely that even you could not detect any signs of illness and usually you have not seen them vomit afterwards. So what is the explanation for grass and plant eating? For one thing, it is known that wild felids and canids in nature are known to eat grass. For example, it is seen in 5-10% of scats and stomach contents of wolves and cougars.

We embarked on a project to get some information about what was going on with grass eating and considered three approaches. We could do a prospective study of normal dogs or cats, under constant monitoring, and with access to grass or other plants and see how often they ate grass and their behaviors before and afterwards. This would have been prohibitively time consuming and expensive because one would have to watch many animals almost 24 hours a day. We could give dogs and cats some grass in capsules and look for physiological changes such as an increase in intestinal motility. Finally, we could do a survey of different pet owners to see what they have observed. The last approach is the one we used (Sueda, Hart and Cliff, 2008. Applied Animal Behaviour Science 111: 120–132). First, we surveyed veterinary students about the frequency of grass eating in their own pet dogs and whether they observed signs of sickness before eating grass and signs of vomiting afterwards. Next, we surveyed a group of outpatient clients bringing their pets to our teaching hospital for their observations on their animals about consuming plants and the behavior before and afterwards. These limited surveys, about 40 for each group, revealed only infrequent signs of illness and only occasional vomiting. Faced with the prospects of the null hypothesis, that plant eating is not particularly related to illness or vomiting, we had to use a large data collection system. We turned to a web-based survey in which we gathered over 3000 responses to a survey. After applying inclusion criteria, the useable surveys were narrowed down to about 1500. We found that, contrary to the common perception that associates grass eating with feeling ill and vomiting afterwards, only about 10% of dog owners reported that their dog frequently showed signs of illness prior to plant eating and only 20% reported their dogs regularly vomited afterwards. The vomiting seemed to be correlated with, rather than caused by, the plant eating.

The behavior of plant eating is less common in cats than dogs. But like dogs, cats do not appear to be typically ill before eating plants nor do they regularly vomit afterwards.

Our current hypothesis is that grass eating mostly occurs in normal dogs and in normal cats, and is not associated with illness or a dietary deficiency, but reflects an innate predisposition that was inherited from wild ancestors and that had an ongoing intestinal parasite purging effect that served as prophylactic treatment for the animals in nature (who were always exposed to intestinal parasites). Whether intestinal parasites in wild versions of the domestic cat are less prevalent than in wild ancestors of the dog, is an open question. Certainly cats are more fastidious about making their feces, the source of intestinal infestations, less available.

Predicting Earthquakes

Coming from California, you can imagine the number of times that I have been asked about reports that dogs and cats, and a number of large animals, seem to act unusually or abnormally prior to an earthquake. These reports usually come in after a major earthquake has hit and investigative reporters ask around the neighborhoods for the damage, and so forth, and are told by animal owners that an hour or two before the earthquake their dog or cat or horse seemed to respond in an unusual fashion. A typical response may be a dog that huddles very close to the owners which was unusual for that time of day.

One hears about such animal reports from earthquakes in other countries, and it has almost gotten to the point where it is commonplace to hear about animals' responding prior to earthquakes. But keep in mind that earthquakes occur everyday and even for those in the United States, there are many instances where there are no reports of unusual animal behavior prior to the event.

So do animals respond prior to earthquakes or not? Is it just that dog and cat owners like to think their animals have an extra sense and they know something is going to happen when we do not?

I was a member of a team from UC Davis that investigated the occurrence of unusual animal behavior prior to earthquakes with a grant from the US Geological Survey that was prompted by the prediction of an impending earthquake in China in 1976 on the basis of a barrage of reports of unusual animal behavior. People were directed to get out of their houses and into safe areas, and when the earthquake hit, thousands of lives were saved. The entire scientific world that investigates earthquakes was quite struck by this rather precise prediction by the Chinese of an earthquake based on unusual animal behavior. The authorities on earthquake prediction wanted animal behaviorists to find out if animals did, in fact, respond unusually prior to earthquakes so that they might attempt to make an instrument that was doing what the animals did.

The results of our investigation of 7 earthquakes in California, South American and Central America, is that only one of these earthquakes was actually preceded by observations of unusual animal behavior that exceeded a background level. We determined that the background level was that residents in about 10% of households, on any given day, would say that a dog, cat, horse, or whatever, acted unusual in the previous week. To say that an earthquake was predicted by unusual animal behavior, one would have to show a level of observation of unusual behavior that significantly exceeded the expected background level. The bottom line of our project was portrayed in the title of one of our papers in (Lott, Hart, Verosub and Howell, 1979. Geophysical Research Letters 6:685-687), "Is unusual animal behavior observed before earthquakes? Yes and no."

The Behavior of Sick Animals

Veterinarians and pet owners alike are aware of behavioral changes when their animals become sick. These signs are recognized as depression, inactivity and anorexia and are often the first indications often that an animal is sick. The acute onset of these behavioral changes is accompanied by a febrile response. There has been a tendency among veterinarians and medical specialists to view the behavior of a sick animal as not particularly adaptive and the result of debilitation and reduced inability to obtain food and water. These signs of sick animals are not a maladaptive effect of illness but rather a highly organized behavioral strategy critical to the survival of the animal if it were living in nature. This topic, presented a decade ago (Hart, 1988, Neuroscience and Biobehavioral Reviews, 12:123-137), is receiving a good deal of research attention nowadays and sooner or later you will probably read about some of the research on so-called "sickness behavior." You heard it here first!

In veterinary medicine our view of infectious disease is shaped by an orientation on the importance of chemotherapeutic and supportive therapy, as well as protection through immunization. It is easy to overlook that animals in nature have been exposed to, and survived, infections with pathogenic organisms through millions of years of evolutionary history. Sick dogs and cats can be viewed in the context of the wild counterpart living in the environment without medical or supportive care. When a wild animal becomes sick with a pathogen it is at a life or death juncture. The behavior associated with being sick—anorexia, depression and inactivity—can be viewed as facilitating the febrile response, putting virtually all of the animal's resources into overcoming the invading pathogen.

Fever, especially coupled with reduction in plasma levels of iron, has the effect of inhibiting the growth of many viral and bacterial pathogens in addition to activating the immunological system. The febrile response is part of a cluster of physiological reactions often referred to as the acute phase response. Fever is very costly, metabolically, and for the response to have persisted over evolutionary time there are, by necessity, potential benefits. It is the cost of the febrile response that has led to the selection of a cluster of behavioral patterns that induce the animal to stay in one place, curl up, and conserve its body resources. This potentiates the febrile response. The anorexia is programmed much in the way that the anorexia of a hibernating animal is programmed: even though it is losing body reserves it does not feel hungry. The behavioral signs of a sick animal, coupled with the febrile response, comprise a non-specific syndrome that applies to almost all mammalian species and many avian species, and it applies to a wide range of diseases regardless of whether it is a fatal disease or transient.

When febrile temperatures reach a certain point they can be associated with tissue damage to the heart, liver or central nervous system. Thus, from this standpoint one might wonder how this response could be selected over evolutionary time. Looked at from the standpoint of a wild animal, a high fever that produces some tissue damage may still prove adaptive if the fever is effective at combating the infectious disease which could otherwise kill the animal. Of course, on a domestic scene we do not have to let things go this far. In this lecture we will touch upon some of the aspects of the behavior of sick animals, and febrile response, that can be coordinated in our overall treatment of animals.