Over coffee at work I have been drawn twice lately into talking about which animals on the farm have the highest and lowest IQ. Judging from the responses to these chats, this is a sensitive topic. Seems that lots of folks had favorites from their youth and still hold these dear enough to feel the need to defend or champion them against any malignment.
The biggest arguments seem to be about horses. Now horses are magnificent creatures. They make fine workers, and are certainly useful and fun to ride. I've been right fond of several that I got to know well over long periods. Like dogs or cats, horses can easily become fast friends. And you can't fault the fine appearance of a good horse. Despite my fondness for them though, I have to admit they they are not very smart. I can tell you from personal experience that they will eat themselves to death without pause. (Ouch! That one's close to home.) A cow would never do that - unless it got into some young alfalfa or other green that causes bloat.
Another vexing thing about a horse is it's uncanny ability to find a problem and get squarely caught up in it. When I was about 15, our farm insurance man came out to walk our pasture. As I was always full of questions then and the man had uncommon patience, I walked with him and fired away. Among other things he told the question machine was this: if you turn a horse loose in a hundred acre pasture devoid of any threat to livestock except for one small fenced sinkhole or other hazard, you can count on the equine brain to find the place pronto. Then, if there is a weak place in the fence around it, he might well get through it and fall into the hole.
As I remember, many a horse has tried to run through a barbed wire fence, and more than a few of them have succeeded in getting pretty scarred up in the process. Now they don't do this everyday - it takes such unnatural provocation as local lightning and thunder, another horse running around in an adjoining pasture, or the thrill of racing about after being turned out in an unfamiliar place. While it's true they can be trained well and out of some of their skiddish behaviour (like police horses), by nature they have plenty of instinctive habits that I have found rather unnerving - like leaping sideways (possibly into the path of a truck) when frightened by a quail flying up.
Two of the smartest and dumbest creatures on our place were both birds - crows and chickens. The foxes on our farm, while pretty savvy, were not the Harvard grads of the animal world as some portray. Our dogs - at least the free-choice hybrids - were pretty bright, and one or two were particularly so. What you hear about pigs being smart is true. They can be hard to outwit when they get loose and are well able to get so if you don't keep things pretty well escape-proof. This is unfortunate, because they can really move when being chased.
Of course, I'm really not fit to judge animal intelligence to begin with. Even the dumbest of the species I have mentioned would never willingly leave a beautiful country location to live in an overcrowded morass of concrete, squarish buildings and bright blinking screens.