Some horses have a hard time keeping weight on. These are commonly known as "hard keepers." They can be any age or breed. To ensure your horse is able to keep weight on, make sure he is wormed regularly and his teeth are checked and floated by a vet every six months to one year. If your horse is suddenly losing weight and you haven't had a problem with it in the past, you should have the vet check him out right away before adjusting his feed. If you have already ruled out worms and his teeth, have the vet run a blood test. This will check for any abnormalities in your horse's body that may be causing him to lose weight.

If you're able to rule out all other possibilities, your horse most likely just isn't receiving enough calories. This could mean that he's not getting adequate amounts of hay or grain, or he's getting poor quality or the wrong type of feed. Sometimes if your horse is fed in a pasture with other horses he'll have to compete to get his food. If he isn't dominate enough in the pecking order, the other horses will chase him away and eat his food and he'll be left hungry. If this is the case, adjust his living arrangements so he can be separated for feeding time.

If you suspect your horse isn't getting fed enough hay, increase the rations. You should feed a hard keeper about 1.5-2% of their ideal body weight of hay per day. If your horse currently weighs about 900 pounds and he should weigh about 1000, your horse should be getting about 15 to 20 pounds of hay a day. They hay must be good quality, too. Cattle hay, or other types of hay that is low in protein and full of weeds and coarse grasses is not going to be good for your horse. Horses need high quality, good, rich hay if they are to stay healthy.

If your horse is currently being fed oats or a COB grain and he needs to gain weight, DON'T triple that amount of grain. It's not healthy for any horse to eat grain that is so high in sugar and starch in such large quantities. Switch his feed to something low in sugar and high in fat and protein. Purina Ultium is an excellent grain for a hard keeper. It's very low in sugars and unnecessary ingredients. It's mainly fat and protein. Adding beet pulp or rice bran to a grain like Ultium is an excellent way to put weight on your horse.

Another great thing to add to your horse's diet is alfalfa. You can buy alfalfa pellets to add to your horse's grain, or you can feed alfalfa hay. They also make alfalfa/grass hay mixes you can feed instead of grass hay. Some horses also do well on straight alfalfa hay. Alfalfa is great for hard keepers because it's very high in protein, which is what most hard keepers lack in their everyday diets.

Source: http://www.associatedcontent.com/article/2420014/how_to_get_your_horse_t...