Equine Colic-Part 1
The Common Risk Factors
Dr. Grahame Best
Ranvet Pty Ltd
The term colic refers to pain in the abdomen of horses. It is not a
single disease, but is the manifestation of a considerable number of
diseases: all of which produce pain, and some of which are potentially
deadly.
Making a specific diagnosis to determine the actual cause of the colic
can be extremely difficult for veterinarians at times.
Because of the multitude of possible causes, it is of value to examine
several excellent recent research reviews which looked closely at the
classification of colics, and at the causative factors, incidence and
mortality associated with these diseases.
The majority of cases of colic occur due to unknown causes, but are
primarily presumed to be associated with intestinal muscle spasm or the
accumulation of abnormal amounts of gas in a portion of the intestine.
In general, colic results due to the distension of the bowel by ingesta,
fluid, gas, or due to a functional impairment of the normal intestinal
motility. In more severe cases, abdominal pain may be the result of
damage to the intestinal wall by reduced blood supply (ischaemia),
inflammation, death of tissue (infarction) or oedema (swelling and
increased fluid).
The causes of colic can be classified by well recognised pathological
categories, including obstruction, strangulation, enteritis/colitis,
peritonitis, as well as by the site involved – stomach, small intestine,
caecum, large colon, small colon, peritoneum, and other organs including
liver, spleen and kidney
Rather than simply listing the types of colic which can occur, it is now
of value to look at what we do actually know about causes, prevalence
and risk factors, as well as strategies to prevent colics.
Nathaniel White, DVM, of the Marion Dupont Scott Equine Medical Center,
Virginia, reviewed the risk factors in the USA in 2002, in his
publication “Prevalence, demographics and Risk Factors for Colic,
www.ivis.org, with the following comments and observations;
Out of 100 horses in the general population, 4-10 cases of colic are
expected in one year.
About 10-15% of the colics are repeat cases, with some horses having 2-4
colic episodes yearly.
Horses that have had a previous colic are three times as likely to have
a second colic compared to a horse that has never had colic.
Most colic signs were simple colic or ileus (no contractions of the gut)
with no specific diagnosis entered in 80-85% of cases.
In one study, 30% of horses with colic were identified by owners but
never seen by vets because the colic was short lived or resolved by the
owner.
Studies of colic cases seen by vets reported a predominance of simple
obstruction or spasmodic colic.
Impaction colics made up about 10% of cases, and obstruction or
strangulating diseases requiring surgery made up from 2-4% of cases.
Universities report that simple colic and impaction colics are the most
commonly reported. When a specific gut location can be identified by
veterinarians, the large colon is the most commonly affected, followed
by small intestine, caecum and small colon respectively. Diseases which
cause strangulation (twisted bowel) have the highest fatality rate- with
the large colon torsions being more common than small intestine
torsions.
Colic is responsible for more deaths in horses than any other disease
except old age. In normal farm horse populations, horse mortality from
all types of colic was 0.7 deaths per 100 horse-years, with a colic case
fatality rate of 6.7%.
Risk Factors For Colic
In some colic cases the cause may be evident, such as in grain overload,
but even in these cases, the exact mechanism which initiates the problem
is often unknown. By looking at known risk factors we can begin to
reduce the incidence by eliminating possible risk factors.
There are internal and external risk factors for colic:
Breed
While no breed is immune to colic, several studies suggest that Arabian
horses have more colic episodes, while some other studies suggest that
Thoroughbreds have more. Standardbreds and Warmbloods tend to have more
inguinal hernias due to the increased size of their inguinal ring.
Age
Young and older horses appear to be less at risk of simple colic, so
middle aged horses are most at risk. Weanlings and yearlings are most
likely to suffer ileocaecal intussusceptions.
Diet
Diet has long been blamed for colic. Course roughage with low
digestibility or particularly coarse fibre is observed to cause
impaction colic. Grain overload significantly increases the risk of
colic and laminitis. Feeds such as lush clover and lush pasture have
been implicated in causing bloat.
Information on
feeding here
When investigated by controlled studies, increased amounts of grain, and
changes in the type of hay and grain fed during the year both increased
the odds of colic compared to horses without grain or changes in feed.
One study also reported that daily feeding of concentrate from 2.5 to
5kg/day and >5kg/day to adult horses increased the risk of colic by 4.8
and 6.3 times respectively, compared to horses fed no concentrate.
Interestingly, controlled studies confirm that pellet feeds and sweet
feeds were associated with an increased risk of colic compared to no
grain fed or single grain diets. Grain diets are also known to decrease
the water content in the colon contents due to a decrease in fibre which
binds to water in the colon. Grain diets are also known to travel
through the stomach much more rapidly than fibrous diets. Grain in the
diet increases gas production, and is much more likely to produce an
environment needed for bloat and intestinal displacements.
The horse stomach is relatively small, and is designed to take in small
quantities of food often. Horses are herbivores, and naturally spend a
large part of the day grazing, continually taking in small quantities of
food. When more intensive management, including work and training
programs, stabling, and feeding 2-3 times daily, occurs, the normal
feeding habits of horses are disrupted to varying degrees. Intensive
stabling and work often require higher energy levels in feedstuffs to
allow the horse to cope with increased work requirements. The higher
energy levels are provided by high grain and concentrate components in
the ration, often at the risk of reducing roughage and fibre levels to
inadequate volumes. The horse digestive system is designed to utilise
roughage and fibre, and any deficiency of fibre will result in digestive
disturbances, including colics.
It is highly important to continue regular feeding habits of horses,
maintaining regular feed volumes and feeding intervals.
Do not work horses hard after a full feed.
Never give large quantities of food to a horse not accustomed to it.
Make feeding changes gradually.
Do not allow an overheated horse to drink cold water until it has cooled
off sufficiently, or the cold water will almost certainly predispose the
horse to colic.
Water horses before feeding. Allow access to water again immediately
after feeding. Horses prefer clean, fresh water available at all times.
A horse will drink anywhere from 22 to 68 litres of water daily,
depending on weather conditions, diet and workload.
Do not feed horses directly off the ground, especially in sandy or fine
gravel regions, as the uptake of sand will predispose horses to sand
colics and impactions.
Avoid sudden feed changes. These will rapidly induce colic in most
horses.
Mouldy feeds, such as hay, are potentially deadly to horses, and
regularly cause colic. Check hay thoroughly, especially any lush, moist
hay which may have been baled while too wet. Never feed mouldy hay to
horses.
Environment & Management
Housing and confinement on farms in the Virginia study were not risk
factors for colic. It does however seem logical that changes in diet or
feeding routine are associated with risk of colic. Certainly large horse
properties report that the routine of feeding grain after being brought
in from pasture to stables increases the colic risk – specifically for
bloat and displacements. Altering this routine by keeping horses turned
out after feeding grain decreases the rate of colic. Similarly, when hay
is available to horses on lush pasture, the hay will be consumed as part
of the diet and colic rate is decreased.
Sand colic and impactions are seen where horses graze on pastures grown
on sandy soils, or where horses are forced to eat off the ground with
predominantly sand or fine gravel.
Previous colic
Horses with a history of colic are at higher risk for more colic
episodes
Parasites
Internal parasites are related to increased colic risks in many studies.
Gut obstructions due to ascarids in foals, tapeworm related colic and
strongyle infections have all been reported as causing colics. Many
reports confirm a decrease in colic after controlling small strongyle
infections on properties with previously high colic incidences.
Tapeworm infestations have been related to increased colic, specifically
with colic associated with diseases of the ileum and caecum including
increasing the rate of serious intussusception at the ileocaecal region.
The general use of ivermectin over the last 20 years has seen a
reduction in reports of colic associated with thrombosis of the cranial
mesenteric artery due to Strongylus vulgaris larvae.
Pregnancy
Mares are reported to have a higher risk of colic by colon displacement
during late pregnancy and lactation, particularly from 60 to 150 days
after foaling. The actual reasons for this are not known, but calcium
levels and alterations in diet including increases in energy due to the
higher levels of concentrates in the diet to support lactation may be
related to the increased risk.
Exercise
Racehorses,
event horses and
endurance horses all have an increased risk
of gastric ulceration which can be linked to some colic episodes. These
horses are often on high grain/low roughage diets which tend to produce
gut acidosis and predispose to colics.
Transport and Traveling
Transport increases the risk of colic in several studies. Many vets
commonly administer a laxative to horses prior to transport to prevent
colic from impactions. These colics may be due to variations in feeding
routine, fluid intake, dehydration, etc.
Weather
Many veterinarians frequently associate weather changes with increased
frequency of colic, but many studies can find no confirmation of this.
Prognosis and Strategies to Prevent Colic
In a second paper, “Prognosis and Strategies to Prevent Colic”,
Nathaniel White discussed the survival issues with colic cases, stating
that predicting survival in horses with colic is often challenging. Any
horse which does not respond to initial therapy may be regarded as
having a much more serious prognosis.
In an effort to assist veterinary practitioners and owners, White
attempted to apply previous knowledge of outcomes for specific diseases.
Case fatality for specific colic diseases varies from a few deaths in
cases of simple colic to as much as 75% in some forms of strangulated
intestine. Simple obstructions of the large colon such as displacements
and impactions have low fatality rates (<10%) whereas simple
obstructions or impactions of the small intestine are somewhat higher at
up to 30%. In recent years reports of fatalities to colic have changed
with earlier horse referral to veterinary surgeries, improved surgical
techniques, better anesthesia, and much improved critical care of
surgical patients. A recent report states short term fatality of small
intestinal strangulation has decreased from 75% in 1983 to 25% in 2000.
The likelihood of fatality following successful surgery is highest in
the 10 days after surgery and discharge.
Prevention of Colic
Consider two factors when trying to prevent colic;
(a) Farm factors
(b) Horse factors
Farm factors include management, use, feeding and environment. The
associated risks on properties with high rates of colic include poor
parasite control, high concentrate levels in the diet, multiple sources
of concentrate feeds – including supplements with high levels of soluble
carbohydrates, chronic water deficiency, excessive use of NSAID’s
(non-steroidal anti-inflammatory agents such as phenylbutazone), rapid
changes in hay or grain diet, and horses in work that are fed large
amounts of carbohydrate and reduced amounts of roughage.
Based on these known factors, colic prevention should start by ensuring
horses have a constant fresh water source, ensure that forage makes up
at least 60% or more of the diet (horse digestion is designed to utilise
forage, not concentrates), and that concentrates (soluble carbohydrates)
are fed at the minimal level required to maintain weight and
performance. Changes in feed should be completed over a 7-10 day period,
and parasite control must be regular and effective.
If you have a property with a high incidence of colics, careful
monitoring of the daily management, plus close measurement of energy,
protein and fibre in the diet should be urgent steps in reducing colic
incidence. It would be extremely valuable to have an independent dietary
evaluation conducted to confirm that the diets you are feeding are
applicable and adequate, as carbohydrate overloads are much more common
than most people would consider. Many owners do not consider, for
example, that bran can have a very high soluble carbohydrate content. If
bran is fed simply as a laxative in a regular grain diet, the soluble
carbohydrate level in a horse’s diet can rapidly be doubled to dangerous
levels.
Other known factors which affect individual horses include confinement
due to injury, lack of opportunity to turn out and graze/exercise,
gastric ulceration, crib biting and excessive air intake during similar
vices. These issues are often related to simple colics. Some difficult
horses may only respond to being on pasture 24 hours a day with a total
forage diet, and this arrangement may not fit in with demands for
performance.
A 1999 publication by Cohen, Gibbs and Woods: “Dietary and Other
Management Factors Associated with Equine Colic”, AAEP Proceedings 1999,
Vol.45:pp96 investigated the association of dietary changes with colic
by asking veterinarians. The following factors in this study were
associated with increased risk of colic:
Recent changes in diet,
Recent changes in type of hay
History of previous colic
Recent change in weather conditions
Recent change in stabling
Arabian breed
Use of an anthelmintic in previous 7 days
Failure to regularly deworm
Age over 10 years
Regular exercise (versus pastured at all times).
The finding that a change in diet during the 2 week period when colic
occurred is a consistent finding with other studies. Often, a change in
the specific type of hay was the only dietary change (hay of poorer
quality is often less digestible, thereby predisposing to colic
impactions. It is also possible that changes in hay cause alterations pH
levels in the colon, volatile fatty acid production, and even in the
microflora populations in the large intestine, predisposing the horse to
disorders of intestinal function resulting in colic).
Colic was regularly associated with recent deworming, irrespective of
the product used. In foals, recent deworming may cause colic associated
with intestinal obstruction resulting from rapid death of ascarids in
the gut, as well as with hatching of large numbers of larval
cyathostomes (small strongyles) from cysts in the gut wall after
deworming kills all adults in the gut.
Recent changes in stabling were frequently associated with increased
colics in this study
In Part 2 of this article, we will look more closely at the commonly
diagnosed colics – causes, likely outcomes, prevention, etc, and the
terminology used when your veterinarian discusses colic.