Horses are individuals and must be fed as suchThere are two obvious problems concerning feed intake: too much and not enough. The former is pretty much a problem of management, and the latter may be, too.
The first thing to remember in feeding horses is this: Horses have no self-regulatory mechanism to control their intake. In other words, they will eat themselves to death. Literally. In the wild, this is not a problem; few mustangs encounter 50-pound sacks of corn behind unsecured barn doors. The outcome is colic or founder or both, and either can be serious enough to cause the death of the animal.
This overeating at one sitting is readily controllable; simply make certain that your horses cannot get to your feed storage areas.

Obesity
Although the above is a very serious and tragic situation, it is not the main problem associated with overeating. The most common problem is strictly man-made: long-term overeating due to being fed too much and/or exercised too little. The result is obesity.
If the feed is palatable, a horse will eat what it is given. To some horses, if it does not move (or moves slowly), it is palatable. And because the horse cleans up by no means indicates that it is still hungry.
Obesity is rarely the horse's fault; it is almost entirely the fault of the person(s) responsible for its care. Each horse is an individual and must be fed as an individual. Just as there are varying requirements for food intake in a group of people, there are varying requirements in a group of horses.
Many times I have seen an otherwise knowledgeable horseman go through a barn and place the same amount of feed in each stall and then bring in a group of 16 broodmares ranging in age from four to 20 years old and in pregnancy status from empty to imminent. Fortunately, this feed regimen is probably all right for most of these mares, but, of the 16, there will be a couple that are a few pounds underweight and two or three that are absolute butterballs.
Feeding outside-in ground or fence feeders-makes it impossible to regulate each horse's intake. Even if each horse is totally respectful (and if pigs fly) of its pasture mates' feeders, it cannot be known which feeder a horse will go to, which makes it impossible to place varying amounts of feed in the different feeders. Here you have the added problem of an aggressive, fast-eating horse hogging more than its share. (This is usually not the obese member of the group, however.)
It is much easier to prevent obesity than it is to correct it, but prevention requires knowing your horses, which, in turn, requires observing them. This is not difficult, yet too many people do not want to take the time to do it. Look at your horses. The 16.3-hand Prince John granddaughter that looks as if she should be pulling a beer wagon probably needs more feed than the 15-hand Tom Rolfe mare that looks too delicate to have ever carried a jockey.
Once the weight is on, however, the problem becomes more difficult. For proper health, you must get that extra weight off those fat animals, but this is not as easy as it sounds. And you cannot dial 94-JENNY. The temptation is there to starve it off, but you run the risk of hyperlipemia, which is a subject for a future article. Suffice it to say for now, you do not want it.
To get the weight off, simply feed less of the grain ration and maintain a proper roughage level. Increased exercise is helpful but, in the case of broodmares, is impractical. With stallions and horses in training, it should be no problem to step up their exercise programs. The weight loss will not be seen quickly as anyone knows who ever tried to diet, but, as your horse will rarely raid a refrigerator, it will come off.

Underweight
There are also several reasons for a horse being underweight, among them improper feeding, parasitism, dental problems, endocrinal dysfunction, and chronic disease. Your veterinarian can help in determining the cause. If it is too few groceries, the remedy is apparent: gradually increase the amount being fed.

Anorexia
Anorexia, or refusal to eat, has many causes and, knowing that a horse lives to eat, it should always be considered serious. To determine the cause in an otherwise normal-acting horse, evaluate the feed. It could be bad (moldy) or it could be from a new sack that was formulated slightly differently. Or it could result from a switch in feeds, which should always be done gradually.
Other causes of anorexia include fever, pain, disease, colic, and disruption of routine (weaning, separation from a buddy, moving to a new farm, etc.). Address the cause and remove it, and the horse will eat again. In extreme cases, nutritional supplementation may be necessary to get a horse over anorexia. This is best done under a veterinarian's care in an equine hospital.
To sum up, all feeding problems must first be acknowledged before they can be corrected. Even though management is frequently at fault, your veterinarian can help you work out the problem and guide you in its correction.