Originally posted by Vermontcat
So I guess there are 4 questions total about crib chewing, fattening up a horse, pecking order and sensitivity to bug bites. Let me know if you need more details.
Lets see. Some of these things may well be tied into each other, a cause and effect type of thing, very much like Shell said.

First, the weight issue is the most crucial. I would suspect, so long as the teeth are in good shape, not needing float or anything, and worming schedule is up to date, that the combination of stress, being at the bottom of the pecking order, the tendency to crib (which can be due to the stress and the lack of weight!), and the sensitivity this horse seems to have, could very well be why he won't keep weight on.

First, I would not completely isolate him, but set up a run for him to have all his own next to where the other horses are. I have a gelding who thinks he is still the boss man, and he will run other horses, primarily geldings, through fence. In the pasture where the other 5 horses are, we sectioned off part of the run-in for him and made a good sized run for him off that to be in. He is right next to everyone, but can't get to them to hurt anyone. This may help the gelding relax enough without adding the stress of being totally isolated from other horses to gain his weight back and stop cribbing.

However, cribbing is a pain in the rear to deal with, once it is a habit, even relaxed horses will do it. It has been theorized that endorphines are released when a horse does this, so it can actually be physically and mentally addicting. It can be started due to boredom, stress, or even mineral/vitimin deficencies.

I have found rather than collars, which often don't work, or only work when they are on (they know when you forget to put it back on), reduce the number of things he can get ahold of to clamp on to. What he can get a grip on, put some heavy duty NASTY tasting stuff on like Bitter Apple (make sure it is the outdoor formula) or even Shreiner's liniment (more expensive and not as long lasting, but MAN that stuff tastes BAD!) I have found other products just don't work, and I have had some BAD cribbers. It is also crucial to make certain the horse has access to a mineral salt block and is supplimented with a good B vitamin suppliment to help with any deficencies.

Once he is separated, he should gain on a typical diet. However, if he doesn't, beet pulp is one way to go to help him gain without making him hot. There are also some suppliments to help with weight gain, or a higher protein and fat diet can help. Adding corn oil to his grain, up to a cup a day, is a great fat addition, but it can make them hot. Or try canola oil, same fat without the corn carbs which make them hot.

As for the bug problem. Feed him garlic, dried and chopped if you can get it, in his grain. I have found that a 1000lb horse getting about 2-3 tbs a day in his grain of the dried (more potent) stuff makes a huge difference. We get mesquitos, no-seeums, and knats out here pretty badly in the summer. This makes a great difference. Also, nothing beats Skin-So-Soft bath oil for a fly spray. Just mist it on him, brush it in, and he is good to go for a couple days. Some people find it a bit strong smelling, but it works perfect. I have actually seen clouds of bugs hanging 2 feet off my horses wanting in, but that stuff offends them too much.

Hope this helps.

BTW, Shell, you had some good points.