These heavy horses show decreased exercise tolerance and increased stress on joints and soft tissue support structures, which
often leads to more injuries. Arthritis can be accelerated by increased body mass as well.
Increased oxygen need
Overweight horses have increased body tissue and alterations in blood flow. This leads to an increase in the amount of oxygen
needed, especially during exercise.
Yet these animals have a harder time taking in oxygen because this increased body mass restricts chest wall motion. This increased
fat layer also makes thermoregulation more difficult and fat horses are more prone to problems during the hot summer months,
which is the peak time for most equine competitions.
Increased heart rate (due to blood flow restrictions) and increased respiratory rate (due to increased oxygen need and attempts
at heat dissipation) can cause increased levels of blood lactate which can lead to tying up or exertional myopathy.
Additionally, increased fat storage in the liver can decrease this organ's function. Increased fat content in the body is
believed to increase the risk of fatty tumors, particularly lipomas, that can grow in the omentum of the abdomen, strangulate
intestine and cause colic.
Obesity decreases immune system function and can make horses less resistant to some diseases.
Overweight mares can have difficulty reproductively and high fat scores have been associated with increased duration of pregnancy,
increased placental weight and decreased milk production as well as difficulty in rebreeding.
Recent research has shown that horses consuming a high-energy diet show exaggerated post-feeding insulin levels and that the
body's response to this dietary challenge can contribute to or cause osteochondritis dissecans or OCD.
This research reported that 100 percent of foals consuming a diet that provided 129 percent of NRC dietary energy recommendations
developed OCD lesions, while only 17 percent of foals consuming 100 percent of NRC dietary energy recommendations developed
These researchers pointed out that modern day equine diets contain high-energy cereal grains that are high in starches and
that such diets are known to increase both blood glucose and insulin levels following consumption.
It is being proposed that such diets are increasing OCD by altering insulin mechanisms in horses.
View from Down Under
Dr. Nerida Richards, a nutritional consultant Ph.D. based in Australia, has a different idea on this new research, however.
She notes that in this new research, horses on the farms with the highest incidence of OCD were 15 percent heavier than the
average of 350 Kentucky weanlings. Weanlings on a farm with a 0 percent incidence of OCD were 3 percent lighter than the average
of 350 Kentucky weanlings.
She postulates, "the elevated insulin responses observed in horses with OCD may be merely a symptom of their excessive body
weight and fatness and not a cause of OCD as has been suggested."
Pretty simple, afterall
All of this information seems to be telling us what we have intuitively known all along.
It is not healthy for horses (or any species) to be overweight, and that treating obesity may, in fact, be much more important
than previously thought.
Treating obesity in horses, however, is probably harder than was previously thought because the answer is diet and exercise
and this becomes a management and compliance problem.
The only way to reduce obesity in horses is to decrease dietary energy intake and to increase exercise.
Often, exercise is difficult for overweight horses so it is best to start slowly. Walking can be a simple first step followed
by easy trail riding and progressing to more strenuous activity, as the horse will tolerate it.
This exercise must be done on a consistent basis and it cannot be stressed strongly enough to clients that it must be done.
Simple turnout on a "dry lot" or depleted pasture is helpful, but not enough. Exercise must be part of the equation to increase
metabolism and to help use stored fat supplies.
Reduce pasture exposure
Pasture grass contains a large amount of energy and horses at pasture graze around 70 percent of the time. This exposure must
Horses are designed to graze and eat continuously, however, so there are limits to the reduction that you can make.
The standard guideline is for a horse to receive at least 1 percent of ideal body weight in grass per day. This equals three
flakes of hay or comparable grass amount per day.
Many horses will be bored on this small amount of hay or grass, and the development of pasture or stall vices such as cribbing
or chewing can be a complication when trying to restrict a horse's intake.
Experts recommend making the horse work harder and longer for its food. Spread the hay out in multiple locations in the pasture
or stall, use a grazing muzzle to slow the horse's intake, place the horse in a larger field or pasture and make it move to
get to water and feed. All of these are small points but may help in reaching the desired goal.