Summarize this article in one sentence.
The temptation when you rescue an emaciated, or very thin, horse is to feed her a lot to help him regain weight. However, this is not as simple as it sounds because suddenly providing an abundance of food causes digestive problems and is likely to trigger potentially serious health issues such as colic or laminitis. Weight gain has to be mapped out over several months. It must be done carefully and methodically. The ideal food for helping the horse regain weight is forage (good quality hay) and the amount you feed the horse should be the amount recommended for her current body weight, plus 10 or 15%.  Use a measuring tape to assess the horse’s current weight, and cross reference this with a body weight-based feeding chart. If you are concerned that you are not feeding the horse the right amount, talk to a vet. After a period of starvation, the horse’s stomach will need to repopulate the good bacteria that aids digestion. Feeding the horse a large meal will put a lot of pressure on the horse’s stomach that could lead to digestion problems. Rather than giving the horse her allotted amount of feed all at once, space the amount of feed you give her out over the course of the day. This will keep the horse from gorging herself. Forage, or good quality hay, is the ideal food for a horse in the initial stages of rehabilitation because it is high in fiber, takes time to chew, and it difficult to bolt down. Bolting a lot of feed quickly can lead to choke, or a blockage of partially chewed, dry food in the esophagus.  Alfalfa hay is high in protein and low in carbohydrates, which can help to keep the horse energized. If the horse is eating hay well, increase her daily ration by about one flake a day, and after a week of eating well, consider allowing her free access to hay. Some horses won't eat hay; if this is the case with your horse, try hay cubes or roughage chunks. These can trick the horse into thinking she is eating a concentrate, which will make her more likely to eat. If the horse if having trouble eating because of dental problems (for example, dropping food or drooling) try soaking the hay cubes to soften them. If the horse is not gaining weight on hay, then add beet pulp or rice bran to her diet. Both foods are higher in calories than forage but are also high in fiber. Avoid beet pulp that contains molasses as it will cause a "sugar rush" or a wash of sugar into the bloodstream that could overexcite your horse. Vegetable oils are an easy way to add calories to your horse’s feed. Most horses will eat 1 to 2 cups (250 ml each) of oil mixed into the food, though some horses may be picky. Try different types of oil, including: Canola, cocosoya, and standard vegetable oil. Although concentrates are high in calories, they are also high in the starches and sugars that trigger metabolic problems such as insulin resistance, colic, and laminitis.

Summary:
Resist the urge to give the horse a lot of food. Plan the weight gain out over several months. Feed your horse small, frequent meals. Feed your rehabilitating horse forage. Troubleshoot if the horse won’t eat hay. Add high calorie foods if the horse is not gaining weight with hay alone. Add oils to your horse’s meal to help her gain weight. Do not give your horse concentrates.