How to help a thin horse gain weight, step by step

Step 1: find out why the horse is thin

The Merck Veterinary Manual says it is important to understand why a horse is underweight, and gives examples: misunderstanding of feeding practices, dental or other health concerns, and pain. Feeding a supplement to a horse whose teeth hurt will not fix the teeth.

Merck's horse owner pages say dental conditions such as broken or irregular teeth are common causes of loss of appetite or weight or a general loss of condition. Signs include slow or difficult eating, stopping while chewing and drooling. They also say heavier worm burdens can cause weight loss, and larval cyathostomiasis is a syndrome of sudden weight loss, often with severe diarrhea, seen in temperate areas in late winter and spring, particularly in horses younger than 5 years (Merck adds it is not common in the United States). Ask your vet to check teeth, run a fecal egg count and look for pain or illness. Our guides to horse dental care and deworming cover those checks.

Step 2: score the body and weigh the horse

Merck says amounts fed should be adjusted to keep a body condition score of 4 to 6 on the 9-point Henneke scale (Henneke and colleagues, Equine Veterinary Journal, 1983), where 6 is the upper limit of acceptable condition and 7 or more is overweight. Emaciated and very thin horses tolerate stress and cold less well and are more prone to infections.

Weigh the horse for a starting number. Merck says weight tapes tend to underestimate and are the least accurate tool, but are useful for tracking change. A girth and length formula gives a closer estimate. Our guide on weighing a horse without a scale shows how. Use the same method every time, and record the score and the weight on the same day.

Step 3: forage first, then fat and beet pulp

Merck's weight gain advice for a healthy horse is better quality forage, slowly adding a high-fat concentrate, adding oil (ideal for underweight metabolic horses that need low-NSC diets) and lessening exercise to help the horse conserve energy. In cold climates it adds clean, dry shelter, forage and a rug or blanket. Merck counts hay cubes, hay-based pellets and beet pulp as forage substitutes, so they can add fiber if the horse cannot eat enough hay. Horses in general need at least 1.5 to 2% of body weight in forage a day on a dry-matter basis.

For fat, Extension.org's feeding management guide describes fat-added feeds as more concentrated in energy and lower in starch, which makes them safer than getting the same energy from more grain. Horses with metabolic problems need your vet's choice of feed. Our own suggestion on supplements: we found no primary source that backs a specific weight gain supplement, so ask your vet which, if any, fits the horse.

Step 4: change slowly

Merck says that for a generally healthy horse with no underlying health issues, slowly increasing caloric intake by approximately 15 to 25% can produce gain over at least 30 to 90 days, and calls this a reasonable starting point from the author's experience. It sets a general goal of 2 to 2.5% of body weight in dry matter for a weight gain diet, forage plus concentrate together. For a 1,000-pound horse that is 20 to 25 pounds a day, our arithmetic.

Extension.org's feeding management guide says to change the amount or form of the ration gradually over several days to weeks, and gives an example of raising grain by half a pound every two to three days until energy balance is met. Merck says gaining 50 pounds can take 30 to 90 days, which works out to roughly 4 to 12 pounds a week by our arithmetic, so a slow start is normal.

Step 5: weigh every one to two weeks and keep records

Merck says to monitor body weight every 1 to 2 weeks during the weight gain process and adjust the diet accordingly. Keep a log with the date, weight, score, feed amounts and any change in teeth, worming or work. If weight stalls after several weeks, call your vet rather than adding feed on a guess.

The refeeding caution: when a horse is very thin

A starved horse is different. Merck says protocols for refeeding starved horses require veterinary monitoring and strict nutritional management, and that rapid introduction of food should be avoided because it can result in potentially fatal refeeding syndrome. Its outline for professionals starts with rehydration, then good-quality leafy hay or alfalfa, about 75% of maintenance energy in at least six small meals over the first 3 days, rising very gradually to 125%. That is the vet's job; do not copy it for a horse at home.

Call your veterinarian or an equine clinic for sudden weight loss, diarrhea, colic signs or a horse that refuses feed. Our own suggestion: do not wait through a 30 to 90 day plan if the horse is very thin to start with, since a vet should direct the feeding.