Weight Gain and Formulating a Feed Program for an Underweight Horse

In this article, we will address the protocol for refeeding a starved horse that one might encounter in a rescue situation, as well as feeding a horse that is merely thin, in order to help it put on weight.

Fighting Starvation

Starved horses are defined as those with a body condition score (BCS) of less than 3 (on the 1-9 Henneke scale), that haven’t eaten anything for five or more days, or that have lost more than 15 per cent of their body weight within two months (unrelated to disease). While it might be tempting to offer them as much food as they can eat, this can actually cause a life-threatening condition called refeeding syndrome.

Refeeding syndrome is the result of a sudden switch from starvation metabolism to the fed state, which shifts the movement and availability of several nutrients, particularly minerals like phosphorus and potassium. This can cause major cellular electrical problems, potentially resulting in cardiac arrest and death. Several research studies have investigated the best practices to safely refeed starved horses and have developed the following protocol.

Scroll to continue with content

Good quality alfalfa hay is the feed of choice in the first 10 days, at amounts indicated in this table, and it will eventually be offered free choice. When the horse is eating well and into recovery, he can be slowly introduced to a high-quality, easily to digest feed, such as a pelleted senior’s ration. It should be noted, however, that even with the best available feeding protocol, and veterinary care, the prognosis is poor, and losses of starved and refed horses are often upwards of 50 per cent.

Encouraging Weight Gain

Feeding a horse to gain weight, especially one with a low body condition score (2-3), to a moderate body condition score (5) is a lengthy process. While there is significant variation among horses (particularly across different sized horses), it has been estimated that one body condition score represents a weight change of approximately 20kgs (45lbs). Therefore, if your horse needs to gain two body condition scores, he’ll need to gain about 40kgs(about 90lbs).

The conversion of food energy to body weight (mostly as fat and some muscle) is not very efficient, and it takes approximately 20Mcal to gain 1kg of body weight. Thus, to gain those two body condition scores, the horse would need to be fed 4Mcal per day above their normal energy (calorie) requirements for 200 days.

The 4Mcal could be easily added to the horse’s ration by increasing his hay intake by approximately 2kg per day (assuming an average energy content of the hay is about 2Mcal/kg, then he would need to be fed 2kg of hay, or about one to three flakes, depending on the size of the flakes). Alternatively, 4Mcal could be given in the form of about 1kg of high-quality commercially available grain mix, or through about two cups of oil per day. While faster rates of gain are possible (with higher calorie intakes per day), it is wise to go slow.

In this example, we’ll use a goal body weight of 500kg, and body condition score of 5, with a horse that is currently has a body condition score of about 3, and weighs only 450kg. For energy requirements, we will add 4Mcal/day to his current (450kg body weight) requirements, but will use protein, calcium and phosphorus, etc. requirements at his goal weight (500kg) requirements.

Some nutritionists recommend adding the 4Mcal/day to the horse’s goal weight energy requirements (rather than his current weight), however, this makes the overall daily feed intake quite high for a thin or lean horse. Instead, if you adjust intake each week to represent the increasing body weight each week, you’ll help his digestive tract progressively adapt to the increasing intakes. Another option is to simply multiply all requirements at a given weight each week by about 125 per cent.

Energy Requirements for Weight Gain

Some dietary options for this example when the horse is at 450kg and requires 18.99Mcal/day are provided. In these diets, I’ve used a slightly higher quality hay than normal, a ‘mixed, mostly grass’ hay, one that would, therefore, have some legume such as alfalfa in it at about 25 per cent. In Example Diet 1, I used a high-quality commercial grain mix example, some oil (to increase calories, but not overload other nutrients) and salt. Vitamin D is a little low in this example, but would only need supplementation if the horse had little exposure to sunlight or if the hay was stored for more than six months. In Example Diet 2, I used oats, a commercial supplement and salt.

Example Diet 1
– 7kg mixed mostly grass hay
– 1.5kg grain mix (with 12% CP, 12% fat, 16% fiber, 1% Ca, 0.5% P)
– 0.1kg oil (about _ a cup)
– 50g of salt (average intake)

Example Diet 2
– 8kg mixed mostly grass hay
– 1.5kg oats
– 50g commercial vitamin-mineral supplement
– 50g of salt (average intake)

Doctor’s Notes
In this year’s series, equine nutritionist, Shannon Pratt-Phillips, Ph.D., will provide some example diets for horses in different classes, but remember these are examples, as each horse is different. In each example, an average 500kg mature body weight will be used, all noted requirements will be taken from the NRC’s 2007 Nutrient Requirements of Horses, and all forage and feed information will come from www.equi-analytical.com and Pratt-Phillips’ own databases.

Obviously, a horse’s diet will differ depending on the quality of hay or feeds offered, and hay analyses are suggested to accurately evaluate your own horse’s diet. If commercial feeds or supplements are warranted in a diet program, Pratt-Phillips will use a fictional formula (and will provide goal percentages for several nutrients), though these may or may not be very similar to commercially available brands. It is suggested that you look for similar feeds, and work with a qualified equine nutritionist to help you select a feed or supplement that compliments your hay to meet the nutrient needs of your horse.