Preventing Laminitis - Dr Jennifer Stewart

Preventing Laminitis in Horses:
Dietary Strategies for Horse Owners
Christine King, BVSc, MACVSc, MVetClinStud, and Richard A. Mansmann, VMD, PhD
Although diet is only one of many factors that cause or contribute to the development of
laminitis in horses, it is by far the most important overall. Thus, implementing the dietary
strategies outlined in this paper can substantially decrease a horse’s laminitis risk. These
strategies can be distilled into one simple phrase: less calories, more exercise. In the words
of Dr. Ric Redden, a veterinarian and farrier, and one of the world’s foremost experts on
laminitis in horses, “Laminitis that is directly associated with obesity is quite easy to
prevent. It’s a simple formula, one I have heard so many times from old horsemen. It’s a
great line for maintaining a healthy horse: ‘The fat ones get less and the thin ones get
more.’”
Clin Tech Equine Pract 3:96-102 © 2004 Elsevier Inc. All rights reserved.
KEYWORDS laminitis risk, dietary strategies, lush pasture, preventable disease, obesity,
insulin resistance, fructan, non structural carbohydrate
Of all the adjectives and epithets that veterinarians have
used to describe laminitis in horses, preventable is not
one that springs readily to mind for most of us. Yet laminitis
is largely a preventable disease. The first step in preventing
laminitis is being aware of all the possible causes and contributing
factors and determining which are most important
in a particular setting. A wide variety of conditions and situations
can cause laminitis or increase the potential for it to
occur (Table 1). Some of these factors are supported by research,
others are suggested by clinical experience. Some can
cause laminitis on their own; in other cases laminitis is caused
by a combination of contributing factors which may not
cause laminitis on their own but, when present together, have
an additive effect.
In 2000, the USDA National Animal Health Monitoring
System published the results of an extensive nationwide survey
on lameness and laminitis in horses in the United States.
Access to lush pasture was the most common single factor,
being attributed as the cause of laminitis in 46% of all cases
(Fig. 1). Grain overload accounted for another 7% of cases,
bringing the contribution of dietary factors to at least 53%.
The results of this survey indicate that, of all the known or
suspected causes and contributing factors, diet is the most
important overall. Fortunately, it is also one we can readily
control and manipulate to substantially decrease a horse’s
risk for developing laminitis.
The key to decreasing the incidence of laminitis in horses is
client education. We must inform our clients—ie, the people who
Address reprint requests to Dr. Christine King, PO Box 1771, Cary, NC
27512. E-mail: christineking@sprintmail.com
96 1534-7516/04/$-see front matter © 2004 Elsevier Inc. All rights reserved.
doi:10.1053/j.ctep.2004.07.010
are managing the horses on a day-to-day basis (horse owners,
trainers, farm/barn managers, and even farriers)—of the risk
factors for laminitis, and assist them in devising and implementing
management strategies which address the factors that are
relevant for the horses at their particular facilities.
This paper focuses on dietary strategies for reducing the
laminitis risk in horses, ponies, and other domestic equids
(hereafter referred to simply as horses). Strategies for minimizing
the incidence or impact of the other risk factors listed
in Table 1 are fairly intuitive and begin with an awareness
that a risk exists. The remainder of this paper is written as a
clinical tool that veterinarians can use for client instruction.
The information can be used as-is or adapted as needed, in
client education materials such as practice newsletters and
fact sheets.
Dietary Strategies for
Reducing Laminitis Risk
Diet is the single most important risk factor for laminitis, and
should therefore be the centerpiece of any program aimed at
reducing a horse’s laminitis risk. The critical component of
the diet is the amount of soluble carbohydrates the horse consumes.
These carbohydrates are the starches and simple sugars
found in plant material that are easily broken down by
enzymes in the horse’s small intestine and/or rapidly fermented
by microbes in the horse’s large intestine. Excess
intake of these starches and sugars, whether in a single meal
or over time, greatly increases a horse’s risk for developing
laminitis.
These readily digestible/fermentable carbohydrates are
also referred to as nonstructural carbohydrates (NSC) or non-

Preventing laminitis in horses 97
Table 1 Known or Presumed Factors that Can Cause or Contribute to the Development of Laminitis in Horses, Ponies, and Other
Domestic Equids
Causes Contributing Factors*
unrestricted access to improved pastures during periods of
high fructan content (eg, spring, fall, cold stress)
grain overload (ingestion of large quantities of dietary starch)
fiber carbohydrates (NFC), as distinct from the fibrous structural
carbohydrates (cellulose, lignin, etc.) which give plants
their structural integrity and support (ie, the plant’s skeleton).
Nonstructural carbohydrates are produced by the plant
during daylight hours (via the process of photosynthesis) and
are used by the plant as an energy source for growth and
reproduction. Any excess NSCs are stored in the leaves and
stems for later use, and, once the plant flowers, in the seeds to
history of laminitis (even if previous episode was mild)
high-grain diet (>5 lb of grain-based feed for the average
sized horse)
severe intestinal disease (eg, “surgical” colic, enterocolitis) consumption of endophyte-infested tall fescue
other serious systemic illness (eg, pleuropneumonia,
overweight (BCS of 6 or greater); the greater the BCS, the
Potomac horse fever)
greater the laminitis risk
endo/metritis secondary to retained placenta pony or Morgan
untreated equine Cushing’s disease (older horses) inactivity
severe hypovolemia (eg, severe dehydration, severe blood occasional strenuous exercise (“weekend warriors”)
loss, toxemia)
exercise at speed on a hard surface (“road founder”)
sustained, nonweight-bearing lameness in one limb (ie, glucocorticoid administration (the higher the total dose,
contralateral limb laminitis)
the greater the risk)
exposure to black walnut heartwood (usually as wood
stress (eg, high-stress occupation or environment,
shavings used for bedding)
transportation, hospitalization?)
small feet for the size or weight of the horse (usually
linked to BCS >6)
flat or thin soles, or excessive trimming of the wall or sole
(ie, less-than-optimal protection for palmar/plantar
digital vasculature)
BCS body condition score (see Table 2).
*These factors, while they may not cause laminitis on their own, appear to increase the risk for laminitis and may cause laminitis when two or
more are present concurrently.
lush pasture
46%
grain overload
7%
unknown
15%
colic or diarrhea
3%
other known
27%
retained placenta
2%
Figure 1 Causes of laminitis identified in a recent nationwide survey
(from Lameness and Laminitis in U.S. Horses. USDA: APHIS: VS,
CEAH, National Animal Health Monitoring System. USDA, 2000).
“Other known” causes included feed problems and complications of
injury, obesity, or pregnancy. Each comprised less than 2% of all
cases, so these diverse factors were combined into one group for this
chart.
fuel germination and sustain the seedling until it can produce
sufficient NSCs of its own.
Grains such as oats, corn, barley, wheat, and millet—
which actually are the seeds of grasses—are high in starch
and simple sugars. Pasture grasses also are high in sugars at
certain stages of their growth cycle and during times of environmental
stress (eg, cold weather). These two feed sources,
grain and grass, must therefore be fed with care in horses.
The circumstances in which excess carbohydrate intake
can lead to laminitis can be divided into two categories:
1. carbohydrate overload—ie, a large meal that is high in
starches or sugars (whether grain or grass)
2. chronic overfeeding (usually coupled with relative inactivity),
resulting in a horse that is overweight.
Either circumstance increases a horse’s laminitis risk.
When both are present, the horse’s risk for developing laminitis
greatly increases, particularly when other triggers (eg,
illness, injury, stress) occur. Following are some dietary strategies
that, when consistently followed, can substantially decrease
a horse’s laminitis risk.
Pasture Management
Access to lush pasture is the single most important risk factor
for laminitis on farms where pasture is available for grazing.
While pasture grasses contain a wide variety of structural and
nonstructural carbohydrates, the ones that appear to be most
important, with respect to laminitis risk, in many of the pasture
grasses in the U.S. are called fructans. Fructans are NSCs
that cannot be broken down by enzymes in the horse’s small
intestine; they bypass digestion and absorption in the small
intestine and reach the large intestine, where they are rapidly
fermented by the resident microbes.

98 C. King and R.A. Mansmann
Mechanism of Pasture-Associated Laminitis
The exact mechanism by which pasture-associated laminitis
occurs is still being researched. What is known is that intake
of a large amount of fructans causes the pH in the large
intestine to drop (ie, become more acidic), as lactic acid is
produced by the fermentation of fructans. The now-acidic
environment in the large intestine kills off the more acidsensitive
microbes and allows the more acid-resistant
microbes to multiply. Certain of these bacteria produce substances
which can activate enzymes (matrix metalloproteinases,
or MMPs) in the hoof wall that break down the cellular
bond which anchors the hoof wall to the pedal bone.
While this step remains to be fully investigated, it is assumed
that these bacterial products reach the tissues of the
hoof via the bloodstream, after being absorbed from the large
intestine into the circulation. The net result is partial or complete
separation of the hoof wall from the pedal bone, and
possibly displacement of the pedal bone under the weight of
the horse’s body and the pull of the deep flexor tendon on the
pedal bone. Pain and distortion of the hoof are the two most
obvious manifestations and hallmarks of laminitis.
Fructan Content of Pasture Grasses
The fructan content of pasture grasses varies greatly with
plant type (species and variety), stage of growth, and growing
conditions, including soil composition, rainfall, temperature,
and hours and intensity of sunlight. Some generalizations can
be made, but it is important to understand that they are by no
means hard-and-fast rules.
1. In general, the fructan content is highest during periods
of active plant growth, such as during the spring and
early summer months. However, it can increase anytime
soil moisture content, sunlight, and daytime temperatures
are sufficient for fructan production. All that
is required for the fructan content to increase in a pasture
is for the rate of production (ie, photosynthesis) to
exceed the rate of use (ie, growth or reproduction). In
many parts of the country, pasture-associated laminitis
is just as common in the fall as it is in the spring; in fact,
it is perhaps more common in the fall, as many horse
owners don’t consider their pasture to be high-risk
once the spring flush has passed. A “green-up” after a
drought is another potentially dangerous period any
time of the year it occurs.
The fructan content may also increase in response to
plant stress, particularly cold stress (temperatures below
40°F). On a bright but chilly autumn day, for example,
the amount of fructans produced by the plant
may exceed the amount used for growth (which is inhibited
by cold temperatures); as a result, fructans accumulate.
Thus, pastures may continue to be a laminitis
risk in the late-fall and even during the winter
months in areas of the country where conditions are
mild enough for horses to graze year-round. It is a dangerous
misconception that only lush spring pasture is a
problem.
2. In general, the fructan content is highest during the day
(when the plant is actively photosynthesizing carbohydrates)
and lowest at night and in the early morning
hours (when the plant is using the carbohydrates for
growth). However, on cool, overcast or rainy days this
pattern may be off by half a day, or more.
In a study in Great Britain, researchers evaluated the
fructan content of a perennial ryegrass pasture on a
warm, sunny day in May and on two cool, overcast or
rainy days in July. On each day, they measured the
fructan content at several different times over a 24-hour
period. As might be expected, the fructan content on
the warm, sunny day was highest between mid-morning
and mid-afternoon, peaking around midday, and
was lowest late at night and in the early morning hours.
In contrast, on the cool, overcast or rainy days, the
fructan content was highest in the afternoon and
evening; it remained high overnight, and was lowest
between dawn and midday.
In that study, the fructan content of the pasture
ranged from 0 to 30% dry matter (which can be enough
to cause laminitis if grazing is unrestricted). On one
overcast day it ranged from 0 to 22% within a 10-hour
period! This study illustrates an important fact: even in
the same pasture, the fructan content can vary greatly
over the course of a day, and it cannot necessarily be
predicted based on the time of day.
3. In general, grass that has already flowered and gone to
seed has a low fructan content. Mature seed heads and
dry, stemmy or “woody” stalks usually are a good indicator
that the grass is low in fructans and other NSCs.
However, flowering grass (ie, grass in the process of
producing seed heads) can be quite high in fructans.
4. In general, the fructan content of pasture grasses is
higher in the stems than in the leaves, particularly in the
lower part of the stems. Overgrazing should therefore
be avoided. Not only does overgrazing cause plant
stress (potentially resulting in an increase in fructan
storage), it means the horse is forced to eat more of the
stem material than when the grass is taller (when more
leaf than stem is eaten). What constitutes “overgrazing”
depends on the grass species (ie, its hardiness and
growth characteristics). With the more upright-growing
pasture grasses, it may be best to suspend use of a
pasture once the grass is grazed down to a height of 4 to
6 inches.
5. In general, native pastures and unimproved grass varieties
are safer for grazing horses than are “improved”
pasture varieties. Among other attributes, many improved
pasture varieties have been selected and bred
for a high NSC content because of the requirements of
dairy farmers for high milk yields in their cows. Some
varieties of improved pasture grasses are very high in
NSCs, including fructans, making these pastures a considerable
laminitis risk for horses at certain times of the
year. In addition, these improved varieties are often
sown as a single pasture crop (a monoculture), whereas
native pastures typically consist of several different
grass species and a variety of other plants.
However, intensive irrigation and fertilization of native or
unimproved pasture varieties can result in NSC levels that
approach those of improved grass varieties, making these
pastures a considerable laminitis risk, particularly for laminitis-prone
horses. Pasture grasses adapted to warm climates

Preventing laminitis in horses 99
(ie, those that grow well in the southern states) tend not to
store fructans as do grasses from more temperate or colder
areas. They can, however, be high in starch and other NSCs
under the right conditions, so they too are a potential laminitis
risk. Tall fescue may present an additional risk if it is
infested with a common endophytic fungus (Neotyphodium
coenophialum). Endophyte-infested fescue has been shown to
increase the risk for laminitis in both horses and cattle.
Grazing Management
Preventing pasture-associated laminitis begins with accurately
assessing each horse’s laminitis risk and managing its
pasture access accordingly. In horses that have had laminitis
in the past, particularly pasture-associated laminitis, and in
those that are overweight, it is best to avoid any grazing of
improved pastures during periods in which the fructan content
is likely to be high. Limited access to native or unimproved
pastures may be less problematic in these horses.
Intake of fructans and other NSCs during high-risk periods
can be limited in a number of ways, depending on the
particular horse’s laminitis risk and on the type and condition
of the pasture:
● limit the amount of time a horse is turned out on pasture
each day (from 30 minutes to several hours, depending
on the risk)
● allow grazing only during relatively low-risk times of the
day (eg, late at night, early morning)
● limit the size of the available pasture by using moveable
fences to create small paddocks (Note: avoid overgrazing)
● use a grazing muzzle which limits the amount of grass
the horse can eat while turned out.
Daily activity is very important for the health and wellbeing
of every horse, but particularly for those that are overweight.
When pasture turnout must be limited or prevented
altogether, the horse should be turned out into a dry lot (ie, a
grassless area) to allow several hours of activity every day.
Inactivity increases a horse’s laminitis risk, especially when
combined with excess body weight.
There are several forage testing laboratories that will test
pasture samples and report on the levels of NSC or NFC in
the grass. When performed periodically throughout the year,
this approach may assist owners or farm managers in identifying
the periods when their pastures are at greatest risk.
However, it is by no means foolproof, as environmental conditions
during any given month can change dramatically
from year to year, even from day to day. Measurement of
NSCs in hay, though, can be very useful in determining
whether a particular batch of hay is suitable for laminitisprone
horses (see below).
Feeding Grain
There are two general scenarios in which grain feeding can
cause laminitis or significantly increase the potential for it to
occur: (1) grain overload and (2) feeding grain to an overweight
horse. The classic example of grain overload is of a
horse that gets into the grain bin and gorges on several
pounds of grain at once. The sequence of events leading to
laminitis are similar to those of pasture-associated laminitis.
The starch in grain can be broken down by enzymes in the
small intestine and absorbed before it reaches the large intestine.
However, with a large grain meal, the amount of starch
consumed by the horse exceeds the ability of the small intestine
to digest and absorb it all, so some of the starch spills
over into the large intestine. Starch is readily fermented by
the microbes in the large intestine, with potentially the same
consequences as those described for fructans.
This problem doesn’t just occur with whole grain; it can
occur with any grain-based feed—ie, any feed in which any
type of grain forms the principle ingredient(s), regardless of
whether or how it is processed. For the average sized horse, it
usually takes at least 5 lbs of starch in one meal to cause
spillover into the large intestine; in small ponies or Miniature
Horses it may take only a pound or two. However, spillover
of starch into the large intestine doesn’t always lead to laminitis;
it depends on how much starch reaches the large intestine—the
greater the starch intake, the greater the laminitis
risk.
Preventing Laminitis
Caused by Grain Overload
Grain overload is a medical emergency. The horse may not
show signs of laminitis for up to 48 hours after overindulging
in grain, by which time it is too late to prevent the damage.
Preventing laminitis in this situation involves calling the veterinarian
immediately it is discovered that the horse has consumed
an excess of grain. Disaster can often be averted by
administering mineral oil or activated charcoal by stomach
tube, if done early enough. Cold therapy (standing the horse
in ice water until 48 hours have passed since it consumed the
grain) may also be an effective means of preventing severe
laminitis in this situation, and well worth the time and effort
it takes.
Preventing this situation in the first place is simply a matter
of being aware of the risk and preventing unlimited access to
grain. Grain storage areas should be secured with a system
that has a built-in back-up (eg, a lockable latch on the feed
room door and latches or bungee cords on the feed bin lids).
Simply making a habit of keeping the feed room door securely
closed, and impressing on everyone who uses the area
to do the same, can prevent a tragedy.
Less commonly, other high-carbohydrate feedstuffs can
cause laminitis when fed in excess. These items include
bread, other bakery products or byproducts, sweet fruits
such as apples and water melons, and lawn clippings. These
feedstuffs are more likely to be fed in large amounts by new
horse owners or well-meaning neighbors who are unfamiliar
with horse management. Preventing laminitis caused by
these feeds is simply a matter of limiting their intake to only
the occasional treat, although lawn clippings should never be
fed to horses.
Overfeeding and High-Grain Diets
The second scenario in which grain feeding can increase a
horse’s laminitis risk is all too common: feeding grain to
horses that don’t need the extra calories and, as a result, are
overweight. This problem is discussed further in the next
section on weight management.

100 C. King and R.A. Mansmann
Table 2 Body Condition Scoring System for Horses
BCS Ribs Spine Pelvis & tail head
Bones of the wither,
shoulder, & neck
1 very prominent very prominent very prominent very noticeable
2 prominent prominent prominent noticeable
3 very noticeable tops of vertebrae very pelvic bones noticeable; faintly noticeable
noticeable
tail head prominent
4 faintly noticeable slight ridge along back pelvic bones covered; can
feel fat at tail head
not obviously thin
5 not visible but back is flat; no crease pelvic bones well covered; rounded withers; shoulder &
easily felt
or ridge
spongy fat at tail head neck blend into body
6 spongy fat over may have slight crease pelvic bones well covered; some fat deposits on withers,
ribs; can feel
individual ribs
down back
soft fat around tail head neck, & behind shoulders
7 obvious filling may have crease down pelvic bones well covered; fat deposits on withers, neck,
between ribs;
can feel ribs
back
soft fat around tail head & behind shoulders
8 hard to feel ribs crease down back very soft fat at tail head; fat fills wither area & behind
fat on inner thighs
shoulders; thickened neck
9 dimpled fat over obvious crease down bulging fat at tail head & bulging fat on withers, neck,
ribs
back
inner thigh; flank filled
with fat
& behind shoulders
Regardless of the horse’s age, gender, breed, height, and body weight, a body condition score (BCS) of 4 or 5 is ideal. Horses with a BCS of
6 or greater are overweight.
In horses that require high-grain diets to meet their energy
needs (eg, those in intense athletic training and competition;
mares nursing young foals), feeding a high-grain diet can
increase the horse’s laminitis risk by altering the environment
in the large intestine, thereby making the resident population
of microbes more susceptible to minor changes in feed composition,
water intake, stress, and other variations in diet and
routine these horses may experience from time to time. Furthermore,
horses on high-grain diets tend to be those in
high-stress occupations—a risk factor on its own for laminitis.
Weight Management
Overweight horses are more likely to develop laminitis when
other risk factors are present than are horses in more ideal
body condition. There are at least three possible reasons why
overweight horses are at increased risk: (1) their greater body
weight puts more load on their feet than when they are in
ideal body condition; (2) overweight horses tend to be fairly
inactive (which on its own is a risk factor for laminitis); and
(3) an excess of body fat often goes hand-in-hand with a
metabolic state in which the horse is less sensitive to the
effects of insulin, a state which interferes with glucose metabolism
(a possible trigger for breakdown of the cellular bond
between hoof wall and pedal bone).
The syndrome of insensitivity to insulin, or insulin resistance,
has received much attention lately as a risk factor for
laminitis in horses. It is sometimes referred to as equine metabolic
syndrome or peripheral Cushing’s syndrome. Typically,
horses with this problem are mature horses that are
overweight (ie, carrying an excess of body fat) and have characteristic
fat deposits along the crest of the neck (“cresty
neck”), over the rump (“apple rump”), and, in some cases, on
the side of the shoulder and in the sheath (males) or in front
of the udder (mares). These tell-tale fat deposits often remain
despite dietary restrictions. Blood tests can be used to confirm
that a horse is insulin resistant, but these tests usually are
unnecessary, as the visual clues are enough.
The propensity for insulin resistance in horses is, in part,
genetically determined. Insulin resistance has been found in
Thoroughbred weanlings and yearlings (especially rapidly
growing foals that are predisposed to developing osteochondrosis)
and in ponies, even ponies in moderate body condition.
So, in at least some of the overweight adult horses and
ponies with insulin resistance, genetics may have played a
significant role, and may even hamper weight loss attempts.
However, simply being overweight causes insulin resistance
(a situation not unlike type II diabetes in humans). So,
whether or not a horse has a genetic propensity for insulin
resistance, overfeeding—ie, providing more calories than the
horse needs to maintain its ideal body condition—is enough
to cause excess fat accumulation, lead to insulin resistance,
and increase the horse’s laminitis risk.
Body Condition Score
What constitutes “overweight” must consider more than just
the horse’s body weight. As is the case in people, body weight
alone can be misleading, as it does not take into account the
height, build, and fitness level (ie, muscle mass) of the individual.
The critical factor in determining whether an individual
is overweight is the amount of fat stored in the body.
In horses, body condition score (BCS) is used to evaluate
the amount of body fat by assessing fat stores in visible areas
of the horse’s body (Table 2). Body condition is graded on a
scale from 1 (emaciated) to 9 (obese). Regardless of the
horse’s age, gender, breed, height, and body weight, a BCS of
4 or 5 is ideal. Horses with a BCS of 6 or greater are overweight.
Obesity (BCS of 8 or 9) is obvious to all but those owners
who are in denial. However, what most horse owners don’t

Preventing laminitis in horses 101
realize is that obesity is a very unhealthy state. Not only is the
obese horse teetering on the brink of laminitis, requiring the
barest nudge to push it over the edge, if that horse does
develop laminitis the prognosis for recovery is far worse than
for a horse in ideal body condition. Although it can be a long
and frustrating process, weight reduction must be a medical
imperative in obese horses if laminitis is to be avoided.
More common, but almost as problematic because the risk
is less obvious, are horses with a BCS of 6 or 7. These overweight
horses are at increased risk for laminitis and other
health problems, yet many owners simply consider these
horses to be well cared for, pleasantly plump, or “easy keepers”;
they are unaware of the health risks, laminitis being
chief among them. It is important that we readjust our perceptions
of what a well-cared-for horse looks like. A horse
with a BCS of 6 or more is not well cared for; it is overfed and
overweight! Weight reduction must be a medical priority in
these horses if the laminitis risk is to be reduced.
Weight Reduction
The approach to weight reduction in an overweight horse is
essentially the same as it is in overweight people. It is simple,
but not necessarily easy. The key is this: calories in must be
less than calories out. In other words, the body must consume
fewer calories than it is using.
Feeding fewer calories is very important, but in many cases
it is not enough on its own. That approach does nothing to
use up the extra calories already stored as fat on the horse’s
body, unless the ration provides significantly fewer calories
than are required to meet the horse’s maintenance energy
needs. However, feeding a horse “starvation rations” (ie, less
than maintenance energy needs) sends the body into survival
mode—ie, preservation mode—which makes weight loss even
more difficult, as the preservation of energy stores becomes a
metabolic priority. Furthermore, feeding severely calorie-restricted
diets to overweight horses (especially ponies and
Miniature Horses) can cause a metabolic condition called
hyperlipemia, which can be life-threatening, and increases
the laminitis risk.
For effective and healthy weight loss, the horse must also
perform more daily activity than it has been doing. The objective
is to use up the extra calories already stored on the
body as fat. This aspect of weight management can be quite a
challenge in overweight horses that already have laminitis or
that are lame for other reasons. However, it is not impossible.
The exercise does not need to be high intensity or high impact;
simply walking the horse each day can be beneficial
(provided the horse’s medical condition allows).
Of course, the more daily exercise the horse performs, the
better for weight loss, but the horse’s current fitness and
comfort must be the guide as to how much exercise (how far
and how fast) to perform at a time. Alternatives to riding
include hand-walking (ie, leading the horse), longeing, free
schooling in a round pen or arena, ponying (ie, leading the
horse while riding another horse), driving, ground driving
(ie, long-lining from the ground), and swimming or wading.
Paddock or dry lot turnout generally is not enough, as most overweight
horses just stand around when turned out.
Grain should not be fed to overweight horses. For one
thing, they do not need the extra calories. In addition,
in some very carbohydrate-sensitive (ie, insulin-resistant)
horses, even a small amount of grain can cause metabolic
alterations that interfere with effective weight loss and laminitis
management. For the same reasons, sweet treats (eg,
those containing molasses or other sugary taste enhancers or
binding agents) and other starchy foods should be avoided.
Grass hay cubes can be a good alternative to sweet treats,
provided the hay cubes do not contain molasses or other
sweeteners, and treats are offered only occasionally and only
in small amounts.
High-fat feeds also should not be fed to overweight horses,
no matter how low their content of starch and sugars. These
feeds do not present the laminitis risk that high-carbohydrate
feeds do, but overweight horses simply do not need the extra
calories. It is stating the obvious to point out that it is counterproductive
to feed fat to a horse that needs to lose fat!
Some veterinarians and horse owners opt to “micromanage”
overweight horses by monitoring insulin resistance using
blood tests and by analyzing every component of the diet
and manipulating the NSC and mineral content accordingly.
While this detailed approach may be needed in some cases, it
is not necessary in the majority of overweight horses. Good
results can usually be achieved simply by eliminating grain
and other high-carbohydrate feeds from the diet, feeding
grass hay of moderate nutritional quality, offering a vitaminmineral
supplement appropriate for that part of the country,
restricting pasture access (as discussed in the earlier section
on pasture management), and providing some type of structured
exercise every day.
Hay Quality and Quantity
The bulk of the fructans and other NSCs in grass persists
during the haymaking process, so some grass hays may be
inappropriate to feed to overweight horses, particularly those
that already have laminitis. These tend to be the hays harvested
from improved pastures and cut fairly early in the
growth cycle of the plant (ie, hay containing few or no seedheads).
Having the hay analyzed at a forage testing laboratory
that offers measurement of NSC or NFC can identify hay that
may be best avoided or fed in limited quantities to these
horses. In general, hay that has a NSC content of less than
15% is most appropriate for these horses.
The hay should be of good overall quality (ie, clean, dry,
and free of mold, weeds, and other debris), but of only moderate
nutritional quality. Mature native or unimproved pasture,
cut after the grass has produced seedheads, is recommended.
Hay cut in the fall should be used with caution, as
cold stress before harvesting may increase the fructan content
of the grass, and thus of the hay.
For horses with little or no pasture access, hay should be
fed at a rate of approximately 2% of the horse’s ideal body
weight per day. For a horse whose ideal body weight is
around 1000 lbs, 2% of body weight means 20 lbs of hay per
day. Some horses need less than that to achieve or maintain
their ideal body weight, but the amount of hay per day should
not drop below 1% of body weight (ie, minimum of 10 lbs of
hay per 1000 lbs).
Supplements
Magnesium supplementation has become a popular tool for
managing weigh reduction and insulin resistance in horses.

102 C. King and R.A. Mansmann
However, while balancing an individual horse’s diet for all
macrominerals may be beneficial, simply adding magnesium
to the diet is unlikely to be of value unless a deficiency of that
mineral exists. It is a commonly perpetuated fallacy that
horse feeds often are low in magnesium. Deficiency of magnesium
in pasture or hay is very regional, and may vary from
farm to farm even within a region. It is best to test pasture and
hay samples for mineral content, and determine that a deficiency
or imbalance exists, before adding magnesium to the
horse’s diet. Adding magnesium is unlikely to be of benefit if
the horse is already receiving adequate amounts of magnesium.
Furthermore, supplementing with magnesium is not a
suitable substitute for exercise as a weight reduction tool.
Supplementing the diet with a source of omega-3 fatty
acids such as flax seed may be helpful in improving the
horse’s overall health and metabolic function, including tissue
repair (eg, recovery from laminitis). Whether or not longterm
supplementation reduces a horse’s laminitis risk
remains to be critically evaluated. Supplementation of microminerals
such as chromium and vanadium appears to be
of little value in managing weight reduction and minimizing
laminitis risk in horses.
Thyroid hormone supplements are sometimes prescribed
by veterinarians to aid in weight reduction for overweight
horses. However, unlike the situation in dogs, in which hypothyroidism
occurs spontaneously and causes weight gain,
overweight horses got that way by being overfed; they have
normally functioning thyroid glands, even if blood tests show
that the level of thyroid hormones (T 4 and/or T 3) in the circulation
is low. (Incidentally, measuring the serum concen-
tration of T 4 or T 3 in any form is not an accurate means of
assessing thyroid function in adult horses nor of determining
the need for thyroid supplementation.)
If thyroid hormone supplementation helps in weight reduction,
it is via an increase in the horse’s basal metabolic
rate, not because the supplement is correcting a thyroid deficiency.
Long-term supplementation (ie, months) with thyroid
hormone must be avoided, as it can suppress normal
thyroid function and lead to relative hypothyroidism if the
supplement is suddenly withdrawn.
Thyroid hormone supplements are not a suitable substitute
for dietary management and daily exercise, and they
should not be used as such. There are no shortcuts to healthy
weight reduction! If thyroid hormone supplementation is
used, it should be in conjunction with, not instead of, dietary
management and daily exercise. It is also important to realize
that giving thyroid hormone supplements does not decrease
the horse’s laminitis risk. Although diet is only one of many
factors that cause or contribute to the development of laminitis
in horses, it is by far the most important overall. Thus,
implementing the dietary strategies outlined in this paper can
substantially decrease a horse’s laminitis risk. These strategies
can be distilled into one simple phrase: less calories, more
exercise. In the words of Dr. Ric Redden, a veterinarian and
farrier, and one of the world’s foremost experts on laminitis
in horses, “Laminitis that is directly associated with obesity is
quite easy to prevent. It’s a simple formula, one I have heard
so many times from old horsemen. It’s a great line for maintaining
a healthy horse: ‘The fat ones get less and the thin
ones get more.’”