Talk with your veterinarian if your horse is too thin. Work together to devise a strategy to help your horse gain weight safely. To do this properly, you need to do more than offer her food. Without the proper knowledge, feeding your thin horse more may not help. Rule out underlying health issues and reduce her stress level. If she spends a great deal of time walking or running along the fence, she's just burning more calories. An animal companion, such as a horse, a pony or a goat, may help your horse stay calm and relaxed.
Check your horse's teeth, especially if he's older. With horses, their teeth keep growing. This may result in an older horse with missing or overgrown teeth. If he's missing teeth, he needs special care; a soft mash diet of senior feed and hay chaff usually works well. Have his teeth floated if they're overgrown -- this includes filing and sometimes snipping. Overgrown teeth can cause mouth injuries and pain, and may prevent proper chewing. Don't float your horse's teeth yourself. Get a farrier or a qualified veterinarian to do it for you.
Follow a deworming schedule. Ask your vet to run a fecal test to determine whether your horse has parasites if you aren't sure of her medical history.
Give your horse psyllium for seven days straight once a month if he feeds from the ground or grazes in places where he can ingest sand -- this can make a horse feel full when he should be hungry. Psyllium cleans out your horse's colon, which enables his body to get back on track so he can digest food properly. This step isn't necessary in snowy areas.
Talk with your horse's veterinarian about vitamins. Supplements may help your horse gain weight.
Avoid grains with a high fat content. High-fat grain puts your horse at risk of developing diarrhea, which will only hinder his progress. It could also dehydrate your horse. Feed your horse a grain that's high in beet pulp. Confer with your vet to figure out the best grain and feeding schedule for your horse.
Don't free feed hay if your horse is particularly thin or emaciated. Limit his roughage at first. His body must work hard to break down and digest hay. Offer him the already somewhat broken down hay chaff -- shake your hay leaves or bales. Slightly dampen this before offering it to him to prevent him from inhaling dust. Don't let damp hay sit for any length of time. Monitor and remove it within a few hours, especially if it's hot outside. Refer to your veterinarian to find out how much broken down hay chaff to give your horse. If he's in bad shape, his vet may not allow hay for the first week.