Preventing Weight Loss in Horses
By Doug Thal, DVM
Clients often bring horses to our veterinary practice with a complaint of weight loss. My approach to
this starts by determining whether the horse is really underweight. Whenever I think about changes in
body weight, there is a specific thought process that I use to try to identify the reasons for it. This
approach is based on an understanding of the balance between a given horse’s energy intake and
energy output. Keeping this in mind, I look at all of the factors that contribute to nutrition and intake on
one hand, and energy expenditure on the other. The purpose of this article is to make horse owners
more aware of this important balance and the factors that affect it. Once this is understood, keeping
horses at optimal weight and health is easier and more intuitive, and cases of weight loss can be
understood and dealt with.
In order to understand whether a horse is underweight or not, it is first important to know what an
“optimal weight” is. This is very subjective. The closest we can come to making an objective judgment
is through an established Body Condition Score System, which rates horses on a scale of 1-9. On
this scale, 1 is emaciated and 9 is obese. Body condition scores of 5 to 6 are considered optimal. The
system is based on muscle and fat cover of the bony landmarks of the body, especially of the top-line
and ribs. Information on body condition scoring is readily available on the internet, and I recommend to
horse owners that they familiarize themselves with it and use it. Scales for horses are generally not
easily accessible. Weight tapes measure the circumference of the girth and relate that to weight. They
are a cheap and practical alternative to a scale and are especially valuable for tracking change. For the
purposes of this article, we will consider significant weight loss to be a state where horses fall out of the
optimum range of Body Condition Score.
Weight loss results from an imbalance between caloric intake and expenditure of energy. Factors
that affect either or both intake and outflow will change the balance and will affect a horse’s weight. If
there is more energy expenditure than caloric intake, then a horse will lose weight.
Let's first discuss expenditure of energy. How much energy a horse expends depends first upon
energy needed for “Maintenance.” This depends on body weight and metabolic rate. Different breeds
and individuals have varying basic nutritional needs for maintenance. The amount of feed necessary for
maintenance of a typical “hotblood” like an Arabian or Thoroughbred tends to be greater (per unit body
weight) than that for a typical “coldblood” like a draft or pony breed.
Beyond energy for maintenance is that needed for additional body functions. Examples of this
? Late term pregnant and lactating mares require maintenance plus the additional energy needed
for growth of the fetus or the production of milk.
? Horses in work expend additional energy in proportion to how much work they do.
? Growing foals require the energy for maintenance plus the energy needed for growth.
Weight loss results from the breakdown and conversion to energy of complex sugars, muscle and
fat from the body. This breakdown is intricately controlled by a complex system of chemical
messengers responding to the body's perceived needs. Expenditure of energy must be balanced by
energy intake in the form of nutrition, or signals are sent to start to break down the body’s stores of
complex sugars, muscle and fat to account for the difference in needed energy, resulting in loss of
these tissues and weight loss.
Nutritional intake is how much nutrition is brought into the circulation from the intestine, and this
relates to what is taken into the body from the diet. There are several steps which are critical for a
horse to achieve necessary nutritional intake.
? A horse must have access to and ingest an adequate amount of high quality feed of the
? He must be able to process this by proper grinding of feed by the teeth. Poor dental function
results in poorly processed feed, which is not well digested and absorbed in the intestine.
? A healthy gut assimilates the needed nutrients into the bloodstream.
Healthy body systems and metabolism will result in the nutrients in the bloodstream being
processed, with the necessary energy used and the remainder put into body stores in the form of
complex sugars, muscle and fat.
Anything which decreases nutritional intake, with everything else being equal, will result in weight
loss. Therefore, the most common reasons for weight loss in horses are:
? Inadequate feed intake or poor feed quality for given nutritional needs.
? Inadequate processing of feed resulting from dental problems.
? Parasite infestation - Parasites compete for nutrition and cause damage to the intestinal
tract, which decreases absorption of nutrients.
? Aside from dental abnormalities, older horses simply have more difficulty assimilating
nutrients from their intestinal tract. For that reason, they require more easily digestible
and absorbable feeds.
? Disease and chronic pain: Sick animals lose weight because energy is needed to heal or
fight infection, often coupled with the fact that they tend not to eat as much. Animals that
are in chronic pain also lose weight. Tumors are a common cause of weight loss in older
horses. Many tumors secrete substances which directly cause weight loss by breaking
down body stores of energy.
Management suggestions to maintain horses at optimal weight, taking into account these
Start by being able to define a horse’s body condition using the body condition scoring system.
Keep in mind that it is more difficult to assess body condition in the winter, when hair-coats are long.
Feel your horse’s body, especially his top-line and ribs, through the thick coat to get a better
Feed the right amounts of the right feeds for maintenance. When designing a feeding program,
keep in mind the basic metabolic differences among breeds and individuals. A young Thoroughbred
race horse will be a much “harder keeper” than a 10 year old Pony gelding. Within breeds, certain individuals will be harder keepers than others. The basis of most equine feeding programs is good
quality forage or hay. Many idle horses without special needs maintain their weight well on grass hay
alone. For others, it will be necessary to account for extra needs when calculating the feed necessary
for a given horse. Think of the feed needed for maintenance, then add in additional feed to account for
these additional factors. For horses that have needs beyond maintenance, additional energy rich
concentrates (grains) and other special feeds may also need to be added in. Calorie-rich
supplements like corn oil or rice bran may be added as recommended by your veterinarian. There are
now many commercial diets available for horses with almost any special need.
? Horses in work usually require more energy rich feeds (concentrates) to keep their weight.
? Old horses often need to be fed special easily assimilated “senior feeds”.
? Foals must be fed to account for growth.
? Breeding stallions, late term pregnant mares and lactating mares are all fed to account for their
additional energy expenditures.
? If horses are fed in a group, be sure that each horse gets the feed he needs. Submissive horses
in a group are often driven off of feed. These horses lose weight while others in the group
become fat. The way to handle this is to segregate compatible horses and horses with similar
nutritional needs into groups. Observe individual horses for weight changes carefully so that any
management changes can be made early. Certain hard keepers may need to be fed separately.
? In all cases, make all feeding changes slowly to avoid digestive upset and other health problems.
? It is considered advisable to lower carbohydrate and increase fat as a source of energy in the
diet whenever possible.
? Continually monitor your horse’s weight, and make changes to feed and management as
? It takes very cold weather to change the amount of feed necessary for a healthy horse. This is
usually not a big consideration in our area.
Other management suggestions
? Maintain all horses on an appropriate parasite control program.
? Keep all horses in good dental health. I recommend an annual or semiannual dental exam by a
veterinarian with an interest in dentistry.
? Work with your veterinarian to identify and treat underlying health problems causing weight loss.
Maintaining optimal weight and preventing weight loss in horses requires a balanced approach. Your veterinarian can help you take into account all of the factors we have discussed to arrive at an
effective management program for your horses. I feel that the best way to accomplish this is through
annual or semi-annual veterinary visits and consultation.
? Thal Equine, LLC