Does your horse have a salt or mineral block nearby? If not, try putting one out and see if that helps reduce the habit. Generally horses that eat manure are horses that are starved or neglected. Has your horse had a past like that? Also, if your horse has been on antibiotics lately, his body could be trying to regulate the microbial content in his gut, since antibiotics kill some of the bacteria that helps him digest food and absorb nutrients.
In general, if a mineral block and salt doesn't fix the problem, there isn't a lot of other things you can do. As far as I know, the habit is harmless.
More than most of the time it is a fiber deficiency. Either feed more hay or add beet pulp to his diet if hay is unavailable. I had a mare that did this and adding beet pulp to her diet, 4lbs dry weight in a day, has stopped it.
I will add my bit, to say that it is most likely a fiber or nutritional deficiency. If there's not adequate rough grazing(not just lush pasture), make sure there is adequate hay for free choice feeding. While a salt/mineral block is a good idea, they usually have little trace minerals & horses relying on them solely are still often left quite deficient. I leave one in the paddock for 'free choice', but also provide a ration balancer, after doing a feed analysis, for my guys.
It is theorized that the Ibizan Hound was brought by Phoenician traders from Egypt to the islands off the coast of Spain around 700-900 BC. The breed became popular on the island of Ibiza, where it was used to hunt rabbit and other small game. Indeed, Spanish hunters use the dogs in packs. The Ibizan Hound was fully recognized by the [COLOR=#009000 ! Important][COLOR=#009000 ! Important]AKC[/COLOR][/COLOR] in 1979. General Description
([COLOR=#009000 ! Important][COLOR=#009000 ! Important]Podenco [COLOR=#009000 ! Important]Ibicenco[/COLOR][/COLOR][/COLOR] ) (Ibizan Warren Hound - Ibizan Podenco) The Ibizan Hound, otherwise known as the Podenco Ibicenco, is a tall, slender, long-legged breed that comes in three coat varieties: smooth-haired, long-haired and wire-haired, although the wire-hair is somewhat rare. The coat can be either white and red, white and tan or solid white or red. The ears are large and triangular, and perk upward, framing amber eyes. The head is long and wedge-shaped, culminating in a convex-shaped, or "Roman" nose, which is either pink or flesh-colored. The neck is long and arched, the body is fine-boned, almost skeletal, with sleek rather than bulging muscles. The front legs are straight, the rear legs only slightly bent, each culminating in "hare-feet" with long toes. Dewclaws may or may not be removed. The tail is long and narrow, and carried low.
Theres a description from another website.
Mine looks like homer simpsons dog, so we called him santa lol