I have a thoroughbred ex-racing horse and can't seem to put any weight on him. His teeth have been checked by a dentist and he has been wormed and received all vaccinations. He is currently on two scoops of hard feed and a scoop of beet pulp per meal twice a day but he cannot seem to gain any weight. Any suggestions on what I should feed him to help him to gain weight? But I don't want to feed him anything that may cause aggression in him.
Horses are grazers, so the primary source of nutrition, should come from forage. (grasses, and/or high quality, clean hay) Everyone has preferences for the type of hay, such as alfalfa, bermuda, orchard, etc., just make sure it's clean, dust and mold free, and make sure your horse will eat it! Some horses don't like certain hays, and won't touch them. Don't count flakes of hay, go by weight of the hay. Rather than going to high fat items, such as oils, or certain feeds, with added fats, try using good nutrition, instead. Fat equates to fake nutrition, since it adds weight, without any real nutritional value. (A horse's daily requirement of fat, is less than 5%.)
There is a simple formula, for calculating how much to feed a horse, and it will work if you want one to gain weight, lose weight, or maintain it's weight, and it's based on feeding to a "goal body weight", or the weight you want the horse to weigh.
Based on a horse's workload, and it's general ability to maintain weight, a horse should be fed between 1 1/2% and 2 1/2% of it's goal body weight, in feedstuffs. (grass, hay, and grain/concentrates) It's best to start with 2% of it's goal weight, and you can re-evaluate the effectiveness, after 21 days, and make adjustments, if needed.
If you don't have access to a livestock scale, use a weight tape, they are accurate, within 10 to 15 pounds, and keep a record of the horse's weight, for reference.
Example: thin horse, who currently weighs 850 pounds, who should weigh 1000 pounds. This horse will be fed a total of 2%, or 20 pounds of feedstuffs, every 24 hours, for the first 21 days. If you feel a need to use grain, feed a minimal amount, of 2 pounds, 2 times per day, of the best quality feed. I prefer pelleted feed, it digests better than whole grains. Feed 8 pounds, of clean, high quality hay, 2 times per day.
At the 21 day mark, evaluate how the horse is doing, and make any adjustments, up or down, as needed. Slow gain, is healthy gain, and avoids health problems, such as founder and colic.