Understanding Equine Colic

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UNDERSTANDING 
EQUINE 
COLIC 
YOUR GUIDE TO HORSE HEALTH 
CARE ANO MANAGEMENT 
T h1• one 
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Fil'$t Edictru1: ~1arcl1 2(1()4. 
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Contents 
l 1·1t-rocl11s."'ri<tn , I C' •• I. I I ' I n I I I I I n .' I I I'.' I . ' '.'' I ' n.''. ' I C' I I ,' I' •• t. I .6 
~117iv the Horse .Is P·rone to Colic 
C_b_apter 1 .... .................................... .............. ..... 18 
DClfining Colic 
Oba·pter 2 ................. ..... ......... ............. ·-····· . ........ 30 
The Coli<~ E:ram.inariori. 
Cl>. a te.r 3 ......................................................... 5.0 
Major Conditions Associated with Colic 
Cl1a ter4 ......................................................... 112 
VeteritU•n> ft.tana;g<nnenc qf Colic 
CJ1npt;er 5 ........................................................... 146 
On-Farm Management qf Horses with Colic 
Cl1a- ter 6 ......... ......... .......................... ............. 152 
Making the Decision for Surgery 
Glossary .. .. ... .. ... ..... .. .. ..... ........ ......... .. ... .. .... ... 1 70 
Index JAA 
Recoiumended Readings ............. .................. 191 
Photo Credits .... ..... ............... ..... ..... .... ..... .... ,.191 
About the Author 192 
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INTRODUCTION 
Why the Horse Is Prone to Colic 
6 
A o equine surgeon friend once said "the person who de-signed the equine intestinal tr"dct must have worked on 
it all day Saturday and taken Sunday off~ His statement l~ hu-
morous but true. The overall "design" of the equine intesti-
nal system is fraught with problems that make it b:ighty St!lr 
ceptible ro permitting intestine to move into places where it 
should not be and out of places where lt is supposed to 
remain. Thereafter, it often gets distended and subsequently 
t'3noot return to Its correct location. Although this is cer-
tainly an overgeoeralization of equine colic episodes, the 
high occurrence of col.le and rhe need for abdominal 
surgery (colic surgery) in rhe horse are much higher than in 
nearly any other species; thus, my surgeon friend's reference 
ro the flaw in the engineering and subsequent design of the 
equine intestinal tract. 
Jo the following pages v;re \Viii explain more fully the oc-
currence of"intescinal accidents" and other causes of many 
types of colic (abdominal paln) that are recognized in the 
horse. To explain thes e conditions, it \viii be necessary ro 
understand some of the basic anaromy and physiology of 
the equine intestinal tract. We will also introduce many 
terms rhat are explalned in the text and in the accompany-
ing glossary. 
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UND ERSTANOING EQ U I NE COLIC 
ANATOMY OF THE EQUINE INTESTINAL TRACT AND ABDOMEN 
In a very broad sense the equine intestinal tract can be 
divided into large sections based on its overall function. These 
sections a.re analogous to the 
same segmen1s char exist in 
most mammals. They include 
the stomach, sn1all in1estine, the 
large intestine, and the small 
colon. The s1on1ach is a large 
sac tba1 Uquefies the feed that is 
ingested b)• rhe horse. Only a 
small amount of digestion 
occurs in the stomach. No nu-
AT A GLANCE 
• A herbivore. Ille horse Is de-
signed to graze. 
• Domestlcotion of the horse Is at 
odds with the natural design of 
ns lntesllno• syslem. 
• The design of tile horse's lntesti-
nol lrocl makes Ille animal prone 
to prolllems such OS colic. 
trients are absorbed through the stomach. Acid from the 
siomach helps 10 break do,vn some feed particles, and an 
enzyme known as pepsin begins prorein digestion. Tn1e diges-
tion only begins in the small intestine that receives Utis lique-
fied feed material from the s1omach. With assistance from tbe 
enzymes secreted b)' the pancreas into the small intestine, the 
~mall intestine is the priniary site for digestion and absorption 
of sugar and stareh (a complex sugar in plants) , protein (that 
SMALL 
INTESTINE 
(DUODENUM) 
;?~ 
RIGHT VENT"RAL COLON 
SMALL 
INTESTINE 
(JEJUNUM) 
/ 
ESOPHAGUS \ 
STOMACH 
'. SMAl.L 
LEFT DORSAL COLON "'-... INTESTINE 
(JEJUNUM) 
RIGHT DORSAL COLON 
CECUM 
/' SMALL INTESTINE .L (ILEUM) 
it:~ RECTUM 
~ 
-
TRANSVERSE 
COLON 
' 
PELVIC 
FLEXURE 
SMALLCOlON 
LEFT VENTRAL COLON 
The horse's lntesllnol trocl. 
Cop nghr0 m;itenal 
8 
\Vey 1/t t Harst I s Prone t o Co l ic 
has been initlally dige~ted in the stomach), and lilL The small 
int'CSliue is also the si.te for absorption of fat..soluble vitamius 
(A, D, E, and K;), calcium, and phosphorous. 
The next se.gment, the large intestine, begins with the 
cecum and ends wtlb the descending colon. Th.e large intes-
rine in the horse works like a large fermentation vat in which 
tremendous nwnbers of bacteria and prorozoa live to facill-
ta.te further digestion nJ plant fiber by their production of 
cmymes that are capable of breaking down this component 
of the equine diet (the horse itself does not have these 
enzymes). This fibec breakdown produces substances called 
· -volatile fatty acids" that cm then be absorbed and used by 
the horse for energy. A second imponant function 1>f the 
large intesrioe is water absorption. Tilis function occurs very 
efficient!}' such that by tb.e final step in the small colon, the 
waste material not used by the horse is formed inco feed 
balls. These are subsequently passed into the rectun1 for 
evdcuatioo throiigb the anus. 
As a herbivore the b.orse is "designed• to graze and, there. 
fore, must be equipped wid1 a capacity to extract nutrition 
from grass and other forage. This process requires an area of 
the intestinal tract where the forage can ferment to rele.ase 
absorbable and usable forms of energy (the volat ile fatty 
acids). 1be horse, a "bindgur" Jermenter, differs fro.m •foregut" 
fermenters such as rumirutncs (<.-actle. sbeep, goats). to horses 
fermentation occurs primarily in specialized areas of tb.e 
lower intestinal tract the cecum and large intestine. 
Ruminants perform this ferin.cntation in the rum.en, the 
larg~• compartment of a four-chambered stomach •system.• 
The h.orsc's intestinal tract begins widl die mouth and 
esophagus. The esophagus of me adult horse. is approximare-
ly I 1/4 to 1 1/2 meters in length. As in humans, it serves to 
pass food and water to me stomach through muscular coo.-
tractions of the esophageal wall. Th.e esophagus opens into 
tbe stomach at tbe esophageal sphincter. 
The size of tbe equine sto.ma.ch, a "j-shape,(J" organ,varies 
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UNDERSTAND /NG EQ UINE COLIC 
but generally bolds bet\veen 8 and 15 liters, depending partly 
on the size of the horse. l'wo distinctly different types of 
mucosa (intestinal lining) exist within the smmacl1. One is 
continuous with tile esopl1ageal sphincter. This mucosa is 
termed the •non-glandular" and "squamous• portion because 
it. does not have any stomach glands that secrete acid, mucus, 
or digestive enzymes. Tbis "non-glandular· portion of the 
;-iomacb extends about haliw'dy into the stomach where it 
m.eets rhe second iype of stomach Un.i.ng called the "glandu-
lar" portion of the stomach. When someone is looking .in the 
stomach With an endoscope, this junction. called the ma.ego 
plicacus, is seen as a distinct Line midway into the stomach. 
From this junction t11e glandular portion of tb.e b'tomacb 
extends to the p)•lorus. The "glandular" harbors the glands 
that produce and release stomach acid and the protein-digest-
ing enzyme pepsin. The pylorus of the swmach is the very 
farthest portion of the stomach from tbe mouth. It tecminates 
in a muscular sphincter, the pyloric sphincter, which leads 
into the first po.rtiou of tbe small intestine. 
The small intestine is generally about 22 meters (6o-65 feet) 
long. Lt is composed of three di~-riuct sections. 'Ille duodenum 
is tbe first segment and is only about a mete.r long. At a.bout 
12 to 15 centimeters from the pyloric sphincter, the pancreat-
ic duct. and bile duce empty into the duodenum (just beyond 
the locarion of the pyloric spbiocter). The next and largest 
segment of the small intesrine is the jejunum. It is highli• 
mobile and exists in several coils pri.ma.ri.I)' within the top 
portion (toward the spine) of the left half of the abdomen. 
The last part of the small intestine Is about a meter long and is 
called the ileum. The small intestine does not hold any signifi-
cant volume since tbe feedstuff travels tbrough relatively 
quickly. If it is "holding" feed, it is probably abnormaL 
The me.sentery (1.igamentous att.ichment of the inte:.'tine to 
rhe body wall) is connected to the top of the abdomen 
(toward the spine) near the first and second lumbar vcrte-
brn.e at the site l..nown as the "root of die mesentery:" Witbin the 
Copyrighlt>d material 
JO 
Wily 1/J t Horse ls Pro11 t 10 Colic 
root of the me;entery exists the large cranial mcsenteric artery. 
The mesentery is wide and fan-shaped and carries numerous 
vessels and nerves to the intestines. ft iS attached to the small in-
testine along its entire length, but because of its fun shape and sin-
gular attachment, it L~ highly mobile and permits tile &nall intes-
tine to mo~'e freely in the abdotnen. llmbcdded widlio the mesen-
rery arc lymph nodes and rat. 
From Ille ileum (last part of the sm.'lU. intestine) arises the large 
structure known as the <.tt-um, \vhkb is comma shaped and aver-
ages about I 1/4 metecs in length with a potential volume of20 
liters or more.Rumiruw.ts and even people have a cecum (io the 
human it is the appendix). However, the fuo<.1:loo and si1..e are 
greatly expanded in the bocse. 'Ib.e cecum, in ho.rsc:s, is a large. 
blllDt-ended ~1CUcture that foro1s sort of a T with the sinall inte& 
tine ( th.e ileum) and large intestine (large colon). The cecum is 
the &1:em of the T. and the small and large intestine connect to it 
but not 10 each other. 
There are rwo different entrances to !he cecum, one from the 
small intestine and one fron11he colon. The cecum .is blind ended 
and Cl<t:ends away fron1 the"connections"(orifaces) to the small 
intestine and large colon. Tue entrance of the ileum into the 
cerum is termed the ilcocccal orifice (one branch of the "top ' of 
the "T") and about ; centimeters from the entrance of the ileum 
into the cecum .is the exlt of cbe L-uge colon from the cecum, cbe 
cecocollc orifice (the second branch of the to p of the "T"). 
Normally, the ileunt exists on !be "underside" (or belly) of the 
horse. The apex or tip of the cecum lies on the abdominal floor 
just to the right of m.idline and about a band's length back from 
the tip of the horse's sternum. 
As its name implies, tile large intestine is larger than the 
other parts of the intestinal. tract. The large intestine, from the 
te.nnioatioo of th.e ileum to the anus of the horse, is about. 7. 5 
to 8 meters in length. Tb.e temis"large intestine • and "large 
colon• are often used interchangeably. However, the large 
colon begins at the cecocolic orifice and extends about 3 to 
3. 7 meters to the transverse colon. The large colon. exisrs in 
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UNDERSTANDING EQ UINE COl,IC 
various diameters. About. 5 to 7.5 centimeters in diameter 
near the cecocolic orifice, it expands to 20 to 25 (.'CJltimeters 
on the floor of the abdomen and reaches a diameter of ap-
proximately 8 centimeters at the pelvic flexure, or tum. After 
this flexure it travels forward tO\\"W the head where it turns 
again at the diaphragmatic. flexure and expands to nearly 50 
centimeters in diameter. This segment is followed by the 
next section of large inte~1i.oe, the iraosverse color.L The large 
intestlnc can really be described as the cc.cum. the large 
colon, the trallS\' erse colon, and sn1all colon. 
As already suggested, the entire intestinal system cannot 
~ within the abdomen in full extension. Therefore, it must 
be folded on itself to fit. The major abdominal turns in the 
horse a.re the sternal flexure, where the right venrrd.I (on the 
floor of the abdomen) colon changes direction and turns left. 
to'vard the tail. 111en the left ventral colon changes direction 
and passes back toward the tail from the sternal flexure to 
n1ro dorsally (tOward the spine) at the pelvic flexure. From 
there the left dorsal colon (on top of the ventral colon nearer 
Lo the spine) courses back toward the bead of the diaphragm, 
turns right at the diaphragmatlc flexure (situated above the 
sternal flexure), and gives rise to tbe right dorsal colon (on 
top of the right ventral colon nearer to the spine). The right 
dorsal colon then courses back again toward the tail and rums 
left toward the middle of the abdomen to become the shorter 
and narrower a-am-..·erse colon The transverse colon joins the 
small colon just below the left kidney. The small colon is 
about 3.5 meters in length and begins at the termJnation of 
the shorter transverse colon. Small colon diameter ranges 
from 7.5 to l 0 centin1eters. The solall colon is foUowed by the 
frnal segment, the rectum. The rectum is about 30 centime-
ters in length befure it e:xi.IS the body by the anus .. 
The lar:ge intestine bas numerous tissue bands that can 
often be feJt on rectal examination. These tlssue bands can 
serve as a guide in identifying what piece of intestine iS being 
felt duriog rectal exanlination. The cecun1 and right and left 
Copyrig~!l'C! material 
12 
IV.6 1 In t Horse ls P~ont to Colic 
ventral colon are segments that have four bands. Tbe left 
dorsal colon has oue band. The right dorsal colon bas three 
bands, and the small colon bas two bands. The small intestine 
does not !rove tbese soft ti5sue bands. 
Other abdominal cavity contents are similar to those found 
i'n other mammals. These indude the bladder and associated 
ureters, kidneys, spleen, liver, pancreas, major vessels, etc. Not 
all of these stn1ctu= c-.to be identified on rectal examination 
(see section on rectal examination, page 37). but many may 
be visualized by ultraSOuod examination. 
DIGESTION IN THE HOR.SE 
The horse's evolution as a forage eater helps in understand-
ing its digestive system, which is designed for continuous 
grazing of grnss fornges. The stomach and the small intestine 
can receive a nearly continuous flov.' of small amounts of 
food. The large intestine has been adapted to extract e.~tra 
nutrition from the fiber content of the forages that pass 
through the smallintestine. 
Domestication of the borse is at odds with an intestinal 
S)'Stem well developed for continual grazing.. Convenience to 
owners, modern equine athletic activities, and space llmita· 
rioos dictate modem feeding practices and force horses to 
receive more concentrated feeds at infrequent intervals, har-
vested and processed for-.ii,oes, and reduced access co pasture 
tbat 1:>ennits natural grazing. Cereal grains and fats have, there-
fore, been artifi<.'illlly increased in the diets of domestic-.ued 
horses. Because the intestinal trd<:t is not "designed" for this 
rype of feeding, we sec more digest.Ive disturbances lo borses 
recch'ing these modern management and feeding pr-dctices. 
Although the anatomy of rbe equine lncestinal trocc is not 
dissln1ilar from that of other mammals, its organization and 
physiologic funcrion differ. From tb.e n1outb t0 the beginning 
of the large intestine ac the segn1ent called the cecum, tbe di-
geStive tract functions similarly to that of humans. Ho·wev-er. 
me horse bas a contparatively reduced capacity for digestion. 
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UNDERSTANDING EQUINE COLIC 
Salivary digei.<ion of carbohydrates occurs in humans and 
other species , but such digestion is minimal in horses. 
Beyond the cecum, the large intestine functions more like 
that of the forestomad1s of a ruminant such as a cov;~ In the 
cecum and large intestine there is continual ferment.ition of 
dietary fiber. Normal function of the hindgut (intesrjnaJ tract 
beyond the small intestine) of die horse is highly dependent 
on an adequate source of diera.ry fiber, and wi.thouc it the 
horse is at risk of developing various dietary imbalances. 
As in humans, a horse's digestion process begins in the 
mouth, \vhere grasping of food and manipulation and 
<.'hewing by the lips, tongue, and teeth allow grinding of feed 
into sn1aller pieces. This is particularly impo.rtant for effici.eot 
digestion of fibrous feeds such as bay and for grinding and di-
gestloo ofwbole grams. For this reason dental <.'lire is impor-
tant to the horse in order to facilitate adequate digestion of 
feeds and 1.0 n1ainrai11 body condition. Dental problems may 
lead to dropping of dun1ps of feed material from the mouth 
(quidding) and may predispose horses to cbo.kc (esophageal 
obstn1ction) and impactlon colic. 
Rate of digestion is dcterru.ined by feed type. For i11Stauce. 
borses may rake more than a half hour to eat one .~ilogr.im of 
hay, 'vhile the coosumpcion of a siroJJar a.mount of coo.ceo-
tnn:ed feed will take as little as LO minutes. '!11i~ translates 
uuo a significant difference in the amount of time the horse 
on a concentrated dkt versus one on forage or a pasture diet 
spends eating. Less tin1e spent earing reportedly l1as been as-
sociated \vitll increased boredon1 :u1d development of vices. 
Chewing produces saliva. Because C'.<ting bay requires more 
chewing time, saliv-.i produ<.'tion for hay is greater tban for 
gr•.ins or concentr.ue. Sali\1'3, \Vhich is b.lgb in bicarbonate, 
moistens the feed and helps to buffer acid secretions in the 
stomach. ·111erefore, diets contalning adequate bay and/or 
pasrurc for.ige produce hig.her levels of ~'alivary secretion and 
decrease tile risk of developing gastric ulcers. Sali•-a produc-
tion is nearly cwo 1tmes greater for ha)' or grass than for 
Copyrigh ~ material 
14 
W.+v 1/J t Horst l s Pron• lo Coli c 
grains and concentrates. 
Once the food enters the stomach, digestion begins. 
However, onJy a limited amount of dlgestion occurs In th.e 
b'tomadL In n:ality, the b'tOmach primarily functions ro liquefy 
the feed in preparation for passage in.to the small intestine. 
The limited digestion that occurs is primarily for initial break-
down of proteins by an enzyme called pepsln. Because the 
stomach produces acid continuously, continual grazing 
permits increased protection from gastric ulcers by the bicar-
bonate introduced from salivary secretions. Continual grazing 
also permits absorption of gastric juices by feedstuff that is 
always in the stomach. Hor.ses that are. fed concentrated diets 
and do not graze in between the concentrate "meals" proba-
bly have long periods of time when there is little or no bicar-
bonate being introduced from the saliva. Nor do they have 
feed in lbe stomach to absorb the gastric juices. This type of 
feeding can predlspose ho.rses to ulcer deveJopmen.t. 
True extraction and absorption of nutrients begin in tb.c 
small itnestine. lnges.ta (the liquefi.ed feed 1naterial released 
fro.m the stomach into the sn1all intesti.ne) passes through 
the small intesti.ne rather quickly. Some ingesta may reach 
the cecum in one hour, and 1nost Will reach this site by 
three hours after ingestion. Things such as me.al size, type 
of feed, and activity level can inftuenc.e the transit time 
through the small intestine, the primary site for digestion 
and absorption of sugar and starch (a co1nplex sugar). The 
most important source of sugar in the horse's diet comes 
fro.m pasture grasses. A significant source of dletary sugar 
may also come from sun-cured hay, but hay forage has an 
overall lower sugar content relative to pasture grass. Some 
sweet feeds con.rain up to 10% molasses; therefore, another 
major source of dietary 5ugar 1nay also be in the form of the 
sugar present in molasses. 
Srarch is a complex form of a carbohydrate in planes that is 
broken down to produce sugar. A tremendous number of 
sugar (glucose) molecules make up the complex structure of 
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UND ERS TA NDING EQU INE COLIC 
the starch molecule in plants. Therefore, tbe breakdown (di· 
gestion) of stareh in feed releases large amounts of sugar for 
abso.rptioo. Stareh is a major component of cereal grains. Oats 
are about 50% starch aod corn may be up to 70% starch in 
content. 1be simple sugars in mola5Ses and grasses are easily 
digested by the horse. However, starch, because of trs molecu-
lar complexity, requires breakdown lo.to less con1plex sugars 
that can be further broken dow·n into simple sugars before 
they can be absorbed like the simple sugars found in molasses 
and grasses. Amylase is an enzyme that is released into the 
duodenum fron1 the pancreas (through the pancreatic duct) 
that initiates the digestion of complex sugar molecules such 
as starch. Ho'lvever, amylase iS produced in limited amounts in 
the horse, relative to other species. Therefore, the smaU intes-
tine of the ltorse can become overwhelmed by excess dietary 
starch.As a general rule, a single grai.n or concentrate meal 
should be no greater than 5 pounds in weigbL Furtbennore, 
the digestibility of starch also varies among different types of 
grain.For insrance,srar:ch in corn is rath« poorly digestible. 
However, grains in most commc.rciall)' producc.d feeds are 
processed to i.mprove the digestibility of starch within th.em. 
Despite rhis processing, there is always significant risk that 
wi.lh large grain meals undigested star:ch may reach the large 
intestine. TI1is can be associated 'l\'itb digestiVe disturbances 
in the large intestine. Punhennore, heavy grain meals fe8ult in 
rapid transit t.ltrougb the stomach and smaU intestine. 
Increased rapidity of transit through the small intestine 
reduces time for tbe small intestine co digest and absorb aV:til· 
able star:ch. Therefore, in addition to cbe increased levels of 
starch in he.avy grain meals, the transit of starch to the large in· 
testioe is further facilitated by reduced time for starch diges-
tion. Pelleted and ground feeds move through faster thao bay 
and grass feeds. The fat-soluble '' itamins (A, D, E, K), calcium, 
and phosphorous are also absorbed in tbe small intestine and 
a horse's daily requirements of vitamins aod minerals are 
usually met wben it ingests a minimu.m of 3 pouods of a com· 
Copyrighl - material 
16 
IVny rfl e Ho rse Is Prone ro Co lit 
mercially produced concentratedfeed. However, for many 
horses these requirements can be met simply by feeding 
high-quality hay or having access to good pasrure. 
Fat and protein digestion also occurs predominantly in the 
>mall intestine. Enzymes from rhe pancreas and in the lining 
of the small intestine are capable of digesting proteins to 
their individual amJno acids, permitting their absorption into 
the blood>'tream. The horse's diet is usually rciativcl:)• low in 
fat, yet hoi:ses do bave the capacity to digest and absorb large 
quantities of this nutrient. Studies of fat in the equine diet 
have indicated t,hat horses can tolerate up to 10% of their 
tocal diet as diecary fat. 
Once ingesta bas passed through tbe small intestine, the nia-
terial moves into the large intestine. This begins 'With the 
cecum, Attached co the cecnnl is the remainder of t he large 
intestine (described in the anatomy section). Sim,ilar to the 
rumen of a CO\v, the cecum and large colon are "fermentation 
vacs• \Vhere mlcrooi:gaoisms including bacteria and protozoa 
perform much of the digestion by producing enzymes 
capable of breaking down fiber. TI1is digesti,on, which does 
not occur in humans, enables any fermenting species to break 
down structural sugars in the fibrous portion of the diet. The 
process rakes much more tin1e rhan the digestive process de-
scribed for the small intestine. h:lgesta that enter the large in-
testine may remain there for up to 48 hours before being 
passed as fecal material. The dietary fiber in the feed is not. 
capable of being digested by the horse's o'vn digcslive 
etrLymes. Dietary fiber is primarily made up of the structural 
componenis of plant material; mammalian digestive processes 
cannot use this energy source. However, because of the sym-
biotic relationship bet'\veen t he ,microorganisms and the 
bo:rse (or od1er fermenting species), cellulose and hemicellu-
lose that <.'ldst in plants are broken down and available for use 
as energy. Ugnin, another form of fiber, cannot be broken 
down by fermentation. Therefore, it is passed in rhe feces. For 
this reason the type of diecary fiber intluences its nutritional 
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UND ERSTANDING EQU INE COI, IC 
value. O~trly mature hay wiU have relatively high amounts of 
Ugnin, which reduces its digestibility aod, therefore, its value 
as a di.erary somce of nutrients and energy. However, youog 
bay, beet pulp, and soy hulls have much less ligoio and much 
m.ore digeStible fiber. "Ibey are, tb.erefore,much more valuable 
to the horse as an energy SOUl'Ce. 
The fermentation process leads to cbe production of a 
group of compounds called volatile fatty acids. They are pro-
duced by the digestion of rbe digestible dietary fiber. These 
volatile fatty acids are acetate, butyrate, and propriooate.111 
addition to these compounds, heat, water, and gas are also 
produced. These volatile fatty acids can be absorbed into the 
bloodstream, where they are ao extremely important source 
of energy for rbe bocse.Vii-.unin K is a by-product of tbe activ-
ity of the microorganisms in the la.rge intestine. It becomes 
available to horses for absorption by their activity. Horses, 
therefore, se.ldom require vitamin Kin the.Ir diet. The mi· 
croorganisms in rhe lac:ge colon and cecum also break down 
protein that enters the large intestine. However, this proteio. 
is not used by the bor:se; rather, the end produce. of this break· 
do\vn is ammonia. Ammonia is then used by the bacteria to 
produce proteiJ1 required for the bacteria's gro\vtb aod sur· 
vi.Va.I - thus rhe ~1'111biotic relarionsbip (both rhe bacteria 
and tbe borse benefit). 1be digestive proces.~ cssentiall)' ends 
al chis point in the lac:ge intestine. Tue remainder of absorp-
tion that takes place is primarily absorption of water in order 
to recover the fluid secreted to aid digestion and passage of 
ingesta. TI1e end result is the formation of concentrated fe<.-al 
balls of waste left over from the digestive processes. 
Having te\7 iewed some of the anatomically and physiologi-
cally signi!icaot factors d1a1 a.re important in the process <)f 
digestion and intestinal transit of feedstuff through the 
equine gastrointestinal S}'•'tem, you will be better able ro un-
derstand man)' factors that ma)' be controlled to b.dp prevent 
colic and some of tile processes that may become disrupted 
when a borse experiences an episode of colic. 
Copyriglil.bd material 
CHAPTER l 
Defining Colic 
.18 
I t is important to define the word colic in order to under-srand its meaning, as it perrains to the horse. A common 
misconception is rhat collc is a specifi.c diagnosis associated 
with a well·<lefined cause. However, colic is, in reality, merely 
a clinical sign and not a diagnosis. The term colic actually 
means, in th.e broadest sense, abdominal pain. Abdominal 
pain is relatively common, even in people, We tend to refer to 
our abdominal pain as "stomach aches." Most of the tlrne 
when people get "stomach aches; we have no idea what bas 
specifically r-.iken place to cause the pain. \Ve also realize that 
we are lik.ely to recover from the clJscomfort without medical 
(or surgical) inren-e.otioo. Therefore, we often never clJscover 
tbe ca:use of our "stomach acbes." lo horses, numerous condl· 
lions, b<>th specific and non-specific, may also lead co abdomi-
nal pain, yet most of these conditions go undiagnosed 
because of the self-Umiting nature of most of the causes of 
coUc. Colic is the manifestation of the cause of abdominal 
pain and not a specific diagnosis of its cause. 
Although animals and humans experience abdominal pain 
(colic), ho.rses, for many reasons, seem especially prone to 
conditions that lead to colic. These reasons have been dis-
cus.sed in the introduction. 
Any condition that leads to the disruption of o.ormal intesti-
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UNDERSTANDI NG EQUINE COLIC 
nal motility Oack of motility or increased or disorganized 
motility) can result in fluid and gas accumulation in the intes-
tine. If this condilion persists, 
the intestines, because of their 
poor attachments to the ab-
dominal wall, may move to 
places where they do not nor-
mally belong. On their way to 
these abnormal locations, the 
intestines may twist or simply 
become lodged or trapped in 
areas that do not allow for the 
normal removal of the intesti-
nal contents and gas. In some 
situations such twisting or en-
AT A GLANCE 
• Cdlc means obdomillol poln. It 
ts nor a speclftc clagnosls. 
• T11e lnlesllne con IWlsl °' 
become lropped In oreGs It does 
nor belong. 
• A number of rtst< factors ore os-
sodaled wftt1 Increased Inci-
dence of collc. lncludir1Q a hlslay 
of colic. cllanoes in feeding pro-
grams, poor paroslle conlrol and 
poor denllll an. 
trapments can also lead to the restriction or complete block-
age of normal blood flO\v to and/or from a segment of the in-
testine. Primary inflammatory conditions of the intestine (en-
teritis) may also affect the intestines, leading to disrupted 
motility and dysfunction of the affected segment. The disrup-
tion of intestinal funetion can icself lead to motility changes, 
pain, and abnormal funetion of other areas not directly affect-
ed by the inflammatory process. Inflammatory conditions 
may also affect the intestine secondary to intestinal displace-
ment and/or restriction of the blood supply. Therefore, a con-
dition causing •colic" can cause a cycle of displacement, in-
flammation, loss of normal function and blood supply, and 
pain. However, it is important to realize that movement of in-
testine to abnormal locations, entrapments, inflammation, 
loss of blood supply, and twists (volvulus) are not necessary 
in order for colic to take place. 
THE INCIDENCE OF COLIC 
The good news is that niost horses that experience colic 
do not usually reach the point where this cycle cannot be 
broken. indeed, the vast majority of colic episodes resolve 
Copyrig~/'ldm;iterial 
20 
Dtfi11ing Colic 
with no or minimal "\'eterinary intervention. The incidence of 
equin.e colic bas been estimated by the USDA's Natiooal Animal 
Kea.Ith Monitoring Syste1n Equine 1998 study at 4 .2 events per 
I 00 horses per year. This he-.i.lth monitoring system w as de-
signed to outline the overall prevalence and occurrence of 
various cypes of disease within the North Ameri.can horse po~ 
ulation. 'lbe 1998 srudy found no difference in the incidence 
of colic among geographic regions. 1be percentage of equine 
operations that experienced one or more colic e\'Cllts ·\vaS 
16.3. Overall, only 1.4% of colic events resulted in SUJ:gi.cal in-
tervention. The btality r.1.te for aU colic even is WJ.S 1 :l %. 
lo this same report neither gender nor use of horse 'vas as-
sociated \vith the incidence of colic. There does, however, 
appear ro be some association between some types of colic 
and gender. For instance, uterine torsion and scrotal hemja-
tlon \vould be expected 10 be gender specific. FUrthermore, 
c.vlonic ton.ion (twisting of the large intestine) appears to be 
more prevalent in mares. Non.etl1eless, gender Is not consis-
tently a factor that affecis incidence of other causes of colic. 
Although gender is not a major lilctor in colic, the stud)' did 
suggest some breeds may appear more susceptible. The 
NAKMS sn1dy found Tbo.rougbbreds are more likely to 
develop colic (10.9 colic events per 100 horses per year) 
lhan siock horse breeds such as Quarter Horses, P'Jinrs, and 
Appaloosas (3.5 colic evenrs per 100 horses pee year) or 
other types of horses (2.9 colic even rs per 100 horses per 
year). According to sever.ii other epidemiological studies, 
Ardbians and ~vunger minlature horses appear to <:X"hibit a 
higher incidence of colic due t0 fecallt.hs (accretions or 
"stones• of fecal material formed '"ithio the intestines) and 
smal.I colon impactions, 'vbilc: Standardbreds n1igbt have a 
higher incidence of scrotal hernias. '!be studi.es did not cite 
specific reasons for these associ.ations. Howe'1ec, it Is in1por· 
tant to reali7.e chat factors other than breed might accollllt for 
the heightened incidence in certain breeds. o~vners of 
cenain types of horses may be more observant of signs of 
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UND€RSTAND ING EQUINE COLIC 
colic, and various breeds may be managed and monitored dlf· 
ferendy. A genetic predisposition to certain gastrointestinal 
diSorders could also be possible. 
Age, too, may affect the incidence of colic. Age group eval-
uation in the NAHMS study found the foUowiog f.K1S: 
• Foals less than six months exhibited colic at a rate of 0.2 
~ents per 100 horses per year. 
• Horses betWeen siX and 18 mouths exhibited 45 C\-ents 
per 1. 00 horses per year. 
• Horses 18 months to five years exhibited 5.9 event's per 
·100 borses per year. 
• Horses five years to 20 years exhibited 4.2 colic ev-en1s 
per 100 horses per year. 
• Horses o lder than 20 experienced 4.2 colic events per 
100 horses per year. 
RISK FACTORS FOR COLIC 
A number of rtsk factors are associated ·with increased inci-
dence of colic. Horses that have a !Ustory of colic occur· 
rences and/or previous colic surgery might be more likely to 
exhibit future bouts. Management fact0rs might also affect 
tbe likelihood of colic episodes. Dietary management prac· 
ticcs such as using certain types of feed, increased amounis 
of feed, and increased concentrations of f'eed may be assoclat· 
ed '"ith higher incidences of colic, lamlnltls (a painful foot 
condition), and endoco.xernia. a condition in \Vhich toxins are 
released from dying bacteria (cell walls) \Vithin tbe body and 
Circulated in the blood. 01a11ges lo the diet, such as in 11le 
rype and/or quality of feed and hay or other dietary forage. 
ntigbt lead to higher colic incidence. 
In realicy, a limited nwnber of risk fact0rs for colic can be 
directly cootrolled b)' owner intervention. Using good 
feediug practices and dietary man-•ge.inent. par•site control, 
and good health practices are prob:1bly the extent of our 
abWty to minimize the rl.sk factors for colic lo the borse. 
Although specific and predictable relationships of feeding 
Copyrigh!t~ material 
Defining Colic 
practices to the incidence of coUc are often unclear, di.etary 
manage.ment is unive.rsally considered to be important. when 
evaluating risk facto.rs associated with developing colic. 
Funhermore, constant access to fresh, palatable water is also 
universally regarded as a controllable facet of n1anagcment 
that may significantly impact the incidence of colic. 
The incidence of colic may be associated with the manner 
in which horses are housed Horses in densely populated en· 
vironmenrs, horses that are being moved from pasture co a 
stall, and horses with unrestticted access to lusb pasture may 
all be at increased risk of colic. Horses that are kept on 
pasrure or that spend more time grazing, provided the grnss is 
not too lush, seem to exhibit fewer <.-olic episodes. 
Changes in activi.ty levels have been associated with colic. 
However, the specific relationship of activity to colic inci-
dence is poorly defined and speculative. There may be an as-
sod.ation of increased incidence of colic with exercise at 
either extreme (lack of exercise and highly intense exercise). 
Regular dental care is thought to be an important comp<> 
nent in preventing colic. However, there is no concrete docu-
mentation of tbls association. Poor mastication can lead to 
maldigestion, esophageal obstructions, and intestinal im· 
pactions. For these reasons (and others) it is advisable your 
borse(s) receive regulac dental care. 
Regular deworming is also considered to be important in 
the prevention of colic. Generally speaking, colic episodes are 
likely to be fewer on fanns that practice good pardsite 
control. However, the manner in which a successful parasite 
contrOl program is instituted varies greatly and depends on 
farm management pr.ictices, horse density, geographic loca-
tion, and economics. Often, parasite control programs are de-
sign.ed to minimize the cyathostome (small stroogyle) infec-
tions in horses. The larval forms of cyathostome parasites can 
encyst in the equine intestine. and are often associated with 
increased colic episodes and/or overall poor health. 
Tapeworm infestations may occur .less frequently but have 
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UNDERSTANDING EQlJrNE COLIC 
also been associated with ~'3rious rypes of colic such as inuis-
susception, ileal impaction, and spasmodic colic (see Chapter 
3). While parasites can trigger colic, deworming medications 
also have been implicated in inducing colic, but whether a 
specific medication is 01ore likely to cause colic is uncl.ear. 
Although there is no real evidence of this relationship, a 
recent deworming could be associated v»ith colic episodes. 
The debate continues and condusions vary about the 
effect of ambient temperatures and weather on the inci-
dence of colic. Warmer conditions have been associated with 
increased dehydration and, subsequently, increased incidence 
of colic. Colder temperatures have been associated 'l'i'ith a 
reduced amount of water consumption and increased inci-
dence of colic . Overall, clear association between such eovi-
rono1eotal factors as temperatures, temperature changes, rain· 
fall , or baro1netric pressure and the incidence of colic bas not 
been shown on a repeatable basis. Nonetheless, clinical expe-
rience and son1e epidemiologic evidence suggesl an associa· 
tjon between teo1perature variables and colic incidence. 
Some specillc horse behaviors have been suggested w 
cause colic. Cribbing is commonly believed to lead to colic 
tbrougb tbe · swuUowing· of air that might accumulate in the 
scomach and intestines. Despite thjs common beJief, no dear 
evidence links cribbing to colic. Nonetheless, it is worrbwbile 
to minimize cribbing regardles.~ of any associationwith colic, 
since it is destructive to tbe horse's teeth and to the objects 
on wh.ich the horse cribs. Wood chewing and pica (indiscrim· 
inate consumption of non-food items) may lead to colic from 
digestive upset and foreign body obstruction. Picu Is probably 
more common in younger horses, and horses th.at chew 
wood may be lacking dietary roughage. 
1be cause(s) of any colic episode often goes undiagnosed. 
Many cinles colic episodes may be initiated by a combination of 
factors. Although some factors are believed to play an associa-
tive role in increasing colic incidence, the reality is most colic 
episodes occur due to undefined caascs and all o r none of the 
Copyrigh~. material 
24 
Defining Colic 
above risk factors for colic may be at work for any one 
episode. 
WHAT'S HAPPENING TO THE INTESTINE DURJNG A COLIC 
EPISODE? 
Io a very geoer.il sense the intestine responds to"upset"io 
predictable ways. The manifestation of the clinical signs of 
colic probably depends on the initial inciting evenr(s) and 
tbe degree to whicb normal intestinal physiology and func-
tion are disrupted. Intestinal inflammation often becomes in-
volved in thi~ disruption. furth.er adding to a self"perpetuating 
cycle of intei.'tinal dysfuncrion. lnflammation may be primary 
(as in an inflammatory intestinal condition) or secondary 
(e.g. , as a result of loss of blood supply, strangulation, and/or 
displacement). As we have aUuded al:ready, the inciting 
event(s) of colic may be poorly defined in most. colic cases. 
Furthermore. they are likely to be multj..face.ted. Regardless of 
the initial inciting cause of a colic episode, the disn1ption of 
i.ntestinal physiology and function leads to alterations i:n io-
tesrinal motility, gas distension of the i.ntestine, changes in 
blood supply and blood drainage, edema (tissue fluid accu-
mulation), and physical destruction of the inside surface of 
the intestine, which normaUy helps to mediate absorption of 
\vater and nutritional elements. 
Along with and because of intestinal dysfunction, horses 
can exhibit pain for several other reasons. Abdominal pain 
can often be te.rmed "visceral pain· or pain associated with 
the abdominal oi:gans. 111.is pain m.1y be of \"'ari.ous intensities 
and difficult to pinpoint. Parieral pain is another type of pain 
associated with a colic episode and with diseases that affe<.'t 
the abdominal cavity itself r.Lther than the organs within iL 
Depending on the cause of che colic and its severity, both 
types of pain n1ay occur. These types of pain are difficult or 
impossible to distinguish by clintL-al signs alone. Visceral pain 
receptors are abundant in the inteStines theo:iselves and are 
sensitive to stretching, tr.iction (pulling), and strong muscular 
Copyrighted material 
UNDERS TANDI NG &Q INE C OLIC 
contr.1crlons or other 1ension.1nflammation may also lead co 
vt5ccr.il pain by direcc. pain-ca.using substances rhat accwnu-
bte with intcstin21 inflam1112ti.on oc b)' loss of blood suppl)• (is-
chemla). Therefore, poor or disorganized motUir)' can cause 
pain bcau.c of the loss of normal ln1~inal function, gas and 
nwd acewnub:t.ion, and/or accumulation of intesi.irul conrcnrs 
thlit fall to move through the intestinal trnet. Prim.'11')' intestinal 
inflammalion and primary intestinal obsrructioris can also 
indtK'e pain and lncesti.oal mo1Hity changes. P:tln and orhe:r 
related i111estinal nervous sysren1 responses have also been 
sho,vn co ha,·c negative effects on intestlnnl motility. These 
changes funher amplify overall intestinal dysfunction thar can 
kad to lnflammalion and further worsen lntt!ilin:ll motility. 
Despite lhe potential for 2 self-enhancing cascade of C'\'enrs, 
no1 all colic episodes ace destined co reach a poin1 of .elf-per· 
peruacing physiological dysfunction. Indeed, for many colic 
episodes. the inciting cause may noc reach the level of SC\'Ctiry 
or may not persist for a long enough period 10 initiate lhe 
cycle. If some of tbe e\--ents of this cyde do t:tkc place, they still 
have the potential to resolve on tbeir O\vn or with re.tatively 
simple intcn•ention before they lend to the st:1ge at whlcll the 
infla1nmacion perpecuates lhe intestinal dysfunction, \Vhich 
itself may add to the inflammatory process. Sl.muh31leous ccis-
tcnce of fat'lors (such as edema, motility disturbance, altered 
blood supply. accumulated ingesta. etc.) in th ls C)'clc probably 
incrc:rscs the likelihood that lhc condition worsens and re-
<1uircs more lntcnsi\"e intcrvcncioo. 'lbc presence of some of 
the more serious lilcrors on their own, such as the loss of blood 
supply. may necessitate lntensh'C lntcn'Clltion. 
In n1orc S<:'rious colic episodes or Intestinal disturbances, 
the inner intestinal lining (mucosa) may become d:un:iged by 
.inflammation and/or inadequate blood supply (ischemia). 
Once 1his happens, eodotoxemia can result from the loss of 
1hc integrity of the lining that norinally ac1s as a barrier to 
bacte:ria and their toxins (endoroxlns).Alrhough it can be 
call5Cd by conditions other than intestinal disease, cndotox· 
25 
26 
Dt/i11 i 11g Co lic 
cmia (the presence of endotoitin fron1 bacteria in the blood) 
is relatively common in cases of intestinal disturbances tilat 
lead to bacterial release of endotoxin and to the subsequent 
absorprion of til.is toXin into the blood through the damaged 
intestinal urung (mucosa). 
l11e bacrecial organisms can cause a dr.u:natic biochentical 
response that leads to a significant release of inflammatory 
mediators throughout the enrire body (shock). Their release 
may lead to poor blood perfusion of the tissues throughout 
the body, abnormal blood clotting, and even death. 
Endotoxemia has been implicated in rhc development of 
laminitis in horses. Horses with severe diarrhea and other 
serious intestinal disrurbances, such as strangulating obstruc-
tions and severe inflammation of d1e large and small intes-
tine, commonly encounter endotoxemia. 
THE CLINICAL SIGNS OF COLIC IN THE HORSE 
Clinical signs of colic are chose changes in behavior or ac-
tivity that indicate abdontinal pain. Although d1ese signs are 
A fool exper1encfng colic. 
relativel)• universal, 
individual horses 
may exhlbtt sllghdy 
different cues and dif. 
ferent intensities to 
che same causes of 
colic. For instance, a 
colicl..1' foal often 
rolls onro its back 
widl its feet in me air. 
Some older horses 
and perhaps certain 
breeds may be more 
stoic than others. 
Such horses may ex· 
perience abdominal 
pain and shO\v few 
c.;opynghted riatenal 
UNDERSTA NDING EQVI NE COLI C 
obvious signs of this pain other than depression or unwilling-
ness to move. Overall, no one knows when a horse is behav-
ing abnormally bener dian an owner who is well acquainted 
with his/her horse's normal behavior. Such individuals may 
pick up on early or subde behavioral changes lhat could indi-
cate a problem. Changes that owners often recognize ea.rly 
may include increased recumbency, failure to finish grain or 
hay, reduced activity eidler in dle stall or in dle pasture. in· 
creased time spent lying down, abnom1al seance, increased 
time required for feed consumpt:ion, reduced fecal produc· 
1.ion, dry or loose feces, poor bai.r coat, and weight loss. 
These changes are important to share wich your veterinari-
an, who does not have the benefit of seeing these day-to-day 
changes in your horse. Therefore, the owner serves as the 
eyes and ears to the episodes lhat have pron1pted veterinary 
intervention.Your veterinarian can use thls i.nformation to 
help evaluate your horse. As in1portant as thls infom1:1tion is, 
you, as che owner, need 10 realize lhat these subtle changes in 
your horse are not specific to any one condition. Therefore, 
lhese signs do not necessarily mean that your horse is experi-
encing coUc. 
Your veterinarian will pe.rform a complete examination 
~· '"'""'""--- ..;.;..,.__ 
Horses thot repeatedlylie down might be experiencing colic. 
Cop: ngh2i m .itenal 
28 
Defin ing Colic 
that may seem to iodude things that do not focus on the in· 
testinal ~)'stem. 1bis is the correct approach since these signs 
can indicate problem(s) in areas other than the intestinal 
tracL During the euminatloo your veterinarian will also look 
for evidence of previous colic episodes such as skin abra-
sions, swollen and reddened skin around the eyes and over 
the hips (from trauma due to rolling), presence or absence of 
feces in the stall, scrapes left in the stall floor bedding (from 
pav;iog), and scrapes or balr found on the walls of the stall 
that may be left from a horse lbat bas been cast or otherwise 
trying ro alleviate discomfort. 
Most horses will manifest abdominal paln clinlcally with 
so1ne important signs. Very mild abdominal pain might only 
be apparent in the IM-havioral changes suggested above. 
However, ho.rses with mild abdominal pain often sho'v one 
or more of cbe following cliniClll signs: 
• pa'ving at the. ground with a fo.relimb 
• stretching out 
• reaching around with the head to the flank. 
• incre-.iscd amount of tim.e lying down 
• poor appetite 
• playing in the 'vater bucket 
• continual shifting of \veight on the hind limbs 
• standing against a wall and moving infrequently 
If abdominal pain contl1lucs or if the condition causes 
more than simply mild abdominal pain, the signs of more 
intense (moderate) abdominal pain may becom.e evident. 
1be Signs lndude the following actlons: 
• persistent movement (even in the stall) 
• frequently pawing at the ground with a forelimb 
• repetitively lying down and then getting back up 
• rolling after lying down 
• grunting 
• kicking at rh.e belly 
• frequently turning the bead to tbe flank 
Clinical manifestations of severe abdominal pain may 
Copyrighted material 
UNDERSTANDING EQU INE COLI C 
include the following signs or behaviors: 
• profuse sweating 
• <..'Oncinuous rolling 
• persistent movement 
• getting up and dO'i\'Il violently 
These lists are only general guidelines for gauging the 
severity of pain. Indeed, individual horses might display other 
manifestations of pain. Furthermore, the signs of colic dis-
played by any horse do not neatly divide into the three levels 
o.f pah1 presented here. For any colick)' horse severdl signs 
from any of the above lists may be present, or there may be 
few or none if the horse is particular!)' stoic. 
\Vith more advanced progression of colic or with certain 
type.s of colic, horses might become more depressed than 
painful. Depression is generally believed co occur as blood 
flow de<..-reases to the intestine and leads to segmental death 
of intestinal tissue and endotoxemla, dehydration, and other 
poor blood perfusion of the body tissues that can be associat-
ed with poor oxygen delivery to the same tl55ues. Many types 
of inflammatory diseases of the intestine produce more de-
pression chan pain. Anterior enteritis, colitis, and peritonitis 
may be more likely to cause greater depression than abdomi-
nal pain without necessaril)' being associated with death of 
the intestine. 
Other than in the instances noted above, greater abdotninal 
pain (colic) is generally associated ·with more severe disease. 
Therefore, strangulation of a segment of intestine that leads 
to loss of blood supply and intestinal death causes more pain 
than an impaction tbat causes intestinal obstruction. 
HO\vever, gas distension of any segment of intestine can be 
extremeJr painful due 10 continuous stretching and tension 
on the intestine and its attachment to the body wall (the 
mesentery). IJ severe abdominal pain that bas been. evident 
gives " 'ay to acute relief and cooofon, the astute vcrerinariau 
is usually considering the possibility of a rupture of a distend· 
eel segment of intestine (stomach or intestinal rupture). 
Copyrigl2.2x! material 
CHAPTER2 
Tlie Colic Examinati on 
T he purpose of this section is to familiarize the reader with the 'vhys and bows of the colic examination. 11lis 
section 'lvilJ not ll1Jlke the horse owner an expect on the colic 
exam. Indeed, this section Is likely to provide i.nfonnation on 
many more approaches and techniques used for (.°"Olic exami-
nations than are required for any one exam. In many situa-
tions the equine ve.terinarian must be eicperi.enced enough 
' vitb colic to •streamline· tb.e examination in the interest of 
time and to make good, expedient decisions. For rbis reason 
it is uncommon to see all of the described techniques and 
procedures being performed in every colic situation. This 
does not mean the owner's horse is getting an inadequate ex-
amination. Many of the procedures described are not appro-
priate for every type of colic episode. Tue veterinarian must 
evaluate the (.'ase, identify (if possible) the type of colic 
present, and tben decide on the need for each of the available 
diagnostic techn1ques and procedures. These. diagnostics and 
procedures and their indications will be described further. 
One of the most important questions for a veterinarian to 
answer is whether he/she beJJeves the horse will require re-
ferr.t.l to an institution at which intensive medical or surgical 
intervention is a va.ilable. For some colic episodes the answer 
to tbis question may be nlore obvious than for others. 
Copyrighted material 
UNDERSTAND ING EQ UINE COLI C 
However, tbc aru.-wer is neither always obvious nor easy. 
Nun1erous factors must be considered before deciding upon 
referral. These £actors are covered later in this book. 
IMPORTANT OBSERVATIONS 
A history of the events tJuu 
preceded tJ1e colic examina-
tion often pro,>ides valuable in· 
formation in interpreting the 
findings. A detailed history may 
not be practical or possible in 
an enlergency. However, any 
history of previous health prob-
lems (including colic), the age, 
AT A GLANCE 
• A general physical examination 
Is on Important port of a cilnlcol 
evolua11on !of colc. 
• Ul1Tosound Is the most common 
diagnostic Imaging technique 
used In colJc exo mila1ions. 
• Nosogosmc inrubotion should 
never be performed by a lay 
person. 
breed, and sex of tJle horse, tJle duration of rhe cUnlcaJ signs, 
the severity and frequency of the colic episodes, recal pro· 
duction, and the time the borse was last judged to be normal 
are helpful information the owner should try to provide. 
Nutrition may also be an appropriate topic to address, since 
it is believed that d1angt.-s in feeding or other £actors of nutrl· 
lion may be involved In the development of colic. Access to 
sand and/or poor-<jualicy forage is note-vorthy. In cenain geo-
graphic areas, feeding improperly cured alfalfa ha)' may be 
linked to colic associated \vith blister beetles. An owner 
should provide the history and specific practices of deworm· 
ing. Access to dean, palatable water is important and should 
be addressed by either Indirect examination or specific dis-
cussion with the veterinarian. Owners/caretakers of mares 
that experience colic should provide breeding histories and 
stages of pregnancy to the examining veterinarian. 
IL is imperative to tell the veterinarian about any and all 
medications administered to the horse, as interpretation of 
the examination findings is likely to be affected by these 
medications. A horse t:IY•t appears to be comfortable during 
the examination but has received repetitive doses of medica-
tion is clearly different than a horse that has received no 
Copyrigl-lbd material 
32 
T!tt Colir Exu111i 11 0 1io11 
medication. However, these rwo horses may be cllnJcally in· 
distinguishable unless the medication history is provided. 
THE PHYSICAL EXAMINATION 
A general physical examination is performed as pan of the 
clinical evaluation of the horse exhibiting colic. This exami· 
nation is termed •general" because it focuses on examination 
parameters that are not specific forconditions most often as-
SC>ciated with a colic episode. However, these parameters are 
important in evaluating the overall current health status of 
the horse (i.e., how stable the animal is at the time of the ex-
amination). The parameters n1ost likely to be evaluated 
The veterinarian listens to the abdomen. 
indude a rectal 
temperature, bean 
rate, respiratory 
rate, capillary refill 
tinle, and an evalua· 
lion of 1he mucous 
membrane color. 
The rectal temper· 
ature must be 
taken before per· 
forming any rectal 
examination 
because air intro-
duced into the 
rectum will falsely 
lo\ver the rempera· 
ture. The normal 
rectal tC01perature 
should usually be 
below 10 I degrees 
Fahrenheit. Normal 
rectal cemperarures 
of foals tend to be 
slightly higher but 
Gopynghted riatenal 
UND ERS TA ND I NG EQU INE CO i. i C 
should generally be below 102 degrees fahrenbeit. to.creases 
in body temperat ure may occur in a normal animal after ac-
tivity, excitem.ent, or anxiety. However, body ten1peratures 
greater than I 03 degrees of'len suggest an inflan1matory 
and/or infectious condition that may be dJrecl'.ly associated 
with or be the cause of co.lie. Colic conditions coouoooly as-
sociated with fevers include anterior enteritis, peritonitis, 
colitis, and intestinal rupture. Low body temperatures are 
often seen with se;rere circulatory dh111rbanee and shock. 
The heart rate, respiratory rate, mucous membrane color 
and moisture, and capillary refill time belp rhe veterinarian 
detero:rioe such tilings as the degree of pain (by beart rate 
and respiratory rate) and compromise of general body blood 
flow and distribution (by heart rate, mucous membrane 
color, and capillary refill time) . A horse with severe distur-
bance of blood flow due to debydra.tion, loss of fluid into the 
intestinal tra<.."1:, uneven and poorly <.'OOrdinated blood distrib-
ution, and endoro:xemln woo.Id be expected to exhibit a high 
be.art rate and dark red to purple dry mucous me1nbranes 
Wi.tb a slow ca.pillary refill time (three seconds or more) . 
Such a llorse may also exhibit a high respiratory race due to 
body acid/baSe disturbance and/or pain. Other parameters of 
hydration may be evaluated, but their interpretation can be 
highly subjective if the state of dehydration is not severe. 
Findings that may further indicate dehydration include pro-
longed s.t.·tn renting after being pioch.ed oo the shoulder or 
neck, slow jugular vein Jllling after holding it off at the base 
of the neck, sunken eyes, depression, and high heart rate. A 
high heart rate is also i.ndicative of abdon1inal pain but can 
also be due to several other f.l.ctors, including dehydration 
and endoto:xemia. The relati'i--e significan.ce of all factors that 
may affect the heart i:ace must be interprel:ed in light of the 
other clioJcal .findings. 
After, or along with, the initial evaluation, the veterinarian 
usually .listens to the abdomen (aus<.'Ults) for evidence of rum-
bling sounds that indicate intestinal movement (termed bor-
Copyriglilil'C! material 
Th t Colic E xa111i11a1io11 
borygou). This evaluation is subjective. The examinlog veteri· 
nariao notes whether there is lack of intestinal sounds. lf 
sounds are present, then the veterioarian notes the frequency 
of intestinal sounds as an indication of intestinal 1notility, their 
intensicy; and location. Although this examination may help 
ascenain an overall impression of intestinal motility, it is not 
very opecific. On occaoion, an experienced veterinarian might 
bear the sound of sand moving in the intestines. These "sand 
sounds" are subjectively assessed and more likely to be beard 
in horses that live iJ1 a.reas with large amounts of sand Jn tlte 
soil . Otherwise, much of the information from abdominal aus-
cultation serves only co answer very general questions regard-
ing intestioal motility. These questions may include t.he fol· 
Lowing: I) ls there any rootility? 2) Does the motility sound 
orga.oi1,ed? 3) Is the motility uniform throughout the 
abdomen? 4) Is the motility decreasing or increasing in inten-
sity, duration, and frequency? 5) Are there any sounds that 
1nay indicate a large gas viscus (an intestinal accumulation of 
gas)? This last question is often addressed by simple ausculta-
tion and by abdomioal percussion using a finger-flicking 
motion to the abdomioal wall. A gas-distended viscus pro-
duces a "ping'soond,similar to the sound of a playground ball 
that"pings"as it hits the pa\<eroent. 
NASOGASTRIC INTUBATION 
Another component of the colic examination can be con· 
sidercd diagnostic as well as therapeutic. 'Ibis procedure is 
nasogastric intubation, or"tubing" as it is commonly termed. 
This proce.dure involves insening a scomach tube into the 
nose aod running the tube down the back of the throat and 
esophagus and into the stomach. This procedure can be tech-
nically difficult to perform and should not be performed by 
any lay person. Improper tubing can result in water, oil, or 
orhe.r substances gettiog into the lungs; Loss of the tube into 
the stomach; esophage-.11 rupture; and other complications. 
One complication relatively common in horses that are dif· 
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UNDERSTANDING EQUINE COLIC 
ticult to rube is a nosebleed. Horses that throw tbeir heads or 
are difficult to rube are at greater risk of nosebleeds, but the 
procedure can cause bleeding in any horse. Owners often 
become highly distressed when their horses have nose 
bleeds. Bleeding often appears to be very severe, and it is 001 
uncommon for an owner to ask if the horse will need a blood 
transfusion. Although tbc volume of blood IO>'t appears to be 
great in a number of these cases, the red blood cell indices of 
tbese horses do not change significantly. It may be helpful to 
remember that the horse is a large anin1al and has a much 
larger blood volume tban people do, often in excess of 40 
liters compared to about ; liters in people. Horses \vitb nose· 
bleeds may bleed 
for some time due 
to the highly vas-
cular nature of the 
nasal lining, but 
nosebleeds almost 
ahvays stop with 
simple rest and, in 
future nasogastric 
inrubalion, avoid-
ance of tile nostril 
that bled. 
The nasogasrric 
tube is usually 
passed to check 
for rentLx (accu-
mulation of fluid 
and/or feedsruff 
on the stomach). 
TWs procedure 
helps to tell the 
veterinarian if the 
ston1ach is en1pry-
ing and/or if Lbe Nasagastric lntubattan. 
--~~~~~~~~~~~~~~~-" 
Copyn J i~d riatenal 
J6 
TAt Coli< Examination 
small intestine is moving fluid and ingesta away from Lhe 
stomach. If these functions are not happening normally, there 
may be substantial amounts of fluid on the stomach. 
Nasogastric intubation is partlcul.arly important in horses 
because they do not have the ability to regurgitate. Fluid and 
ingesta may accumulate in the stomach because the horse is 
incapable of vomiting. 11\is fluid must therefore manually be 
removed with a nasogascric tube to prevent spontaneous re-
fluxing of the accumulated fluid up !be esophagus and out of 
the nose due to the pressure from d1e overdistended stomach. 
If nasogastri.c intubation is not performed, pressure continues 
to develop in the stomach and the horse is at risk of stomach 
rupn1re. Horses \vith severe fluid accumulation may reflux 
spontaneously from the nose due to backpressure created by 
excess fluid and gas. Spontaneous reflux from the nose is not 
n.ormal and, unfortunately, does not provide enough pressure 
release from the stomach to prevent stomach rupture. 
Spontaneous reflux from die stomacb, therefore, indicates 
severe pressure in che stomach. The refltLx chat reaches the 
top of the esophagus can be aspirated into the trachea and 
lungs. Thus, spontaneous reflux must be immediately treated 
by nasog;istric intubation of the stomach to prevent both aspi-
ration pneumonia in die lungsand possible stomach rupture. 
Fluid accumulation can cause signifi.cant pain and stretching 
of the stomach and, ultimate.ly, rupture of the stomach. 
Obstructions that can cause fluid staSis in the stomach 
include any strangulating physical obstructions of the intes-
tine downstream from the stomach, most commonly small in· 
testinal physical obstructions (small intestinal volvulus, stran-
gulating lipoma, etc.), or functional obstructions in which the 
loss of normal intestinal function and motility leads to fluid 
and ingesta accumulation. 
Nasogastric Intubation is also performed to administer 
several therapeutic compounds. These include water, elec-
trolytes and water, mineral oiJ, dioctyl sodiumsulfosuccinate 
(DSS), magnesium sulfate (epsom salts), psyllium hydrophilic 
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UNDERSTA N D /NG EQ UrN E CO I,tC 
mucilloid (Mctamucil®) , and ochers. These compounm; wiU 
be addressed in the section that covers therapeutic manage-
ment of colic. It is imperative to realize that. it can be ex-
tremely dangerous to attenlpt to tube your own horse or to 
have. an untrained individual perform chis procedure. Due to 
inappropriate placeo1ent of nasogastric tubes through the 
esophagus and into tbe chest cavity, horses have died from 
mineral oil deposited into the lungs and from other major 
con1plications. Furthermore, severe nasal, pharyngeal, and 
esophageal trauma can occur, and nasogastric tubes can slip 
out of the band of the person operating the tube and be sub-
sequently lost into the .lungs or into the stomach. 
TiiE RECTAL EXAMINATION 
A rectal examination is another c.on1ponent of the colic. ex-
amination. When a rectal examination is performed, the vet-
erinarian is able to feeJ only about one-third or slightly more 
of the abdomi.oal contents through the rectal wall. In other 
words, all of the abdomen is palpated with the tissue of the 
rectum o\rerlying the hand of the examiner. The information 
provided br this examination is not always specific .. Indeed, 
even a veterinarian experienced in rectal palpation may not 
be able to gamer more information other than large or small 
intestinal distension, large intestinal disp.lacement, impaction 
of the large intestine (intestinal overfill of the large intestine), 
twisting of large intestinal bands or, occasionally; evidence of 
intestinal herniation (such as into the scrotum of a stallion). 
Son1e palpable specific structures that the ·veterinarian \ViU 
seek to identify may include the pelvic flexure of the large in· 
testine, the cecum and ventral band of the cecum, the tail of 
the spleen, the left kidney, the ligament becween the kidney 
and the spleen, and the bladder. Finding twisted banm; of the 
large i.ntesti.ne often helps to loc.alize and to identify the 
cause of a colic episode. There. may only be an overaU inl· 
pression of normal versus abnormal rectal findings relative to 
the veterinarian's experience. 
Copyrig~0d material 
38 
Th e Golie E xllm in11rio11 
Although some veterinarians advocate rectal examination 
of every horse that exhibits colic, such an approach may be 
unwarranted and even dangerous to som.e horses. Horses 
that do not exhibit abdominal pain and have a normal physi-
cal examination might be appropriately dis.missed fron1 the 
rectal examinarlon. Funhermore, young aod/o.r fractious 
horses that appear to be otherwise normal by examination 
pose significant pote.nrial danger for rectal tears. 
Consequently, the veterinarian must weigh the relative bene-
fits of the rectal exa.ml.nation versus the danger for rectal 
tears. Horses that do not receive rectal examination should 
not have gastric reflux when the oasogastric tube is passed. 
Performing a nx.'tal examination requires some precautions 
to minimize tbe dangers of rectal tears. Such precautions 
include appropriate rest:rairn and twitching of the horse, pe.r-
formance of th.e examination in as confined an area as is phys-
ically possible (sucll as in a stall), S<..-dation, i,.'OOd lubrication of 
the band and a.rm of the examiner, and good tecbniqi1e that 
minimizes forceful introduetion of the hand and arm against 
straining by the aninlal. Other techniques include the addition 
of lidocaine to the lubrica.tion jelly, epidural anesthesia, and 
administration of small doses of propaotheline to minimize in-
testinal smooth muscle cont:rdction. 
A veterinarian must interpret the information provided by 
recr:d examination because the palpation findings will be 
useless and uninterpretable to anyone who has not received 
specific veterinary training. The rectal examination is always 
potentially dangerous but can be performed safely \vbeo 
proper precautions are taken and when performed by an ex-
perienced ~ererinarian. As an O\vner, you should realize that 
even with all of these precautions, rectal tears do happen. 
Horses that are being examined rectally are likely to be dehy-
drated, have distended and weakened inteb'tioal walls, and be 
unable to Stand quietly due to abdominal pain. NoJletheless, 
the rectal examination is generally regarded as an appropri-
ate and necessary part of the evaluation of horses \vith colic. 
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UNDERSTAND ING EQUINE COLI C 
Horses tba1 have no1 recei~ed a rectal exarn.inarioo oo the 
fir.;t colic exan1 but require a repeat exa.mination due to per-
sistent or recurrent colic should receive a rectal examination 
on the follow-up examination. 
ADDITIONAL DIAGNOSTICS 
Sever.ii other procedures and diagnostics may be performed 
on the horse that exhibits abdominal pa.in. These include ab-
donlio0<.'COresis (' .. belly rap·), complete blood count and serum 
biocbe.mlstry, ultraSOnography, sand sedin1entation examina-
tion, microbiology, endoscopy, laparoscopy, and cxplor.itory ce-
lioromy. ~tany of these procedures are not easily performed on 
a faan or barn visit due to lack of necessary equipment and per· 
sonnel as well as financial consideratio1ts. Abdominoceotesis 
and complete blood count and serum bioch.emistry samples 
can be obtained in th.e field. However, appropriate evaluation of 
these samples must talce place at a veterinary hospical or labora-
tory that bas the appropriate equipment. 
Abdominocentes/s (Aspiration of Abdominal Fluid) 
Abdomioocentesis is performed oo horses to evaluate the 
cell types and protein concentration of the abdonlinal fluid. 
Th.e abdonlinal fluid is "sampled" by p lacement of a l 1/2-
inch needle into the abdomen, usually at its lo,vest point. 
Fluid is "caught" in blood tubes for evaluation of cell counts 
and types, cell morphology, and for prorein evaluation. 
Longer needles may be required to obtain fluid in some in· 
stances. This procednre can pro~;de indirect but important 
ioformatioo regarding the presence or absence of inflamma-
tion and/or infection or bacterial contamination of the ab-
dominal cavity. This procedure is relatively standard practice 
at most referral instilutions and can provide funher evidence 
of the nee.ct for surgical intervention or can indicate another 
non-surgical abdominal disease that requires sped.fie medical 
therapy and management. Tue sample that is obtained might 
also be submitted for culrure and sensitivity if there is evi-
Copyrig~P<)d material 
Th e Co l ic Exami11a1ion 
dence of infection \vithin the abdominal cavity. 
Blood evaluation 
At n1ost referral centers a complete blood count and serum 
biochemistry are pertormed in the standard protocol for eval-
uating a horse with colic. This e\'llluation helps assess major 
organ function, may provide evidence of an infectious concli-
tion. tbat cou.ld be associated witb tbe colic episode, helps 
the inflammatory• response, evidence of significant endotox-
emia, and may provide evidence of dehydration and its sever-
ity. Ce:rtain dues in the blood also might inclicate intestinal 
leakage of protein that could be directly o.r indirectly associ-
atedwith the cause of the colic episode. l'>fajor organ func-
tion can be significantly disturbed in numerous intestinal and 
non-intestinal disorders. The evaluation of parameters rela-
tive to kidney. liver, and other organs can help identify organ 
damage that is either the primary cause of the colic or is 
present as secondary dysfunction to the p.rimary cause of-the 
colic (sudl as that seen "1th eudotoxemia). Low white. blood 
cell counts are relatively common in horses with endotox-
emia and/or diarrhea . The blood count and biochemistry 
help indicate the overd.!l stability of the horse. The common 
abnom.1alities on serum biochemistry include electrolyte dis. 
rurbances and acid/base disturbances (usuaUy acidosis -
excess acid in the blood). 
Sand sedlrnentotton 
Sand sedimentation is easily performed by collecting fecal 
material and suspending it in ·water within a rectal sleeve 
(the above-the-elbow gloves veteri.na.rlans use to perform 
rectal examinations). Horses that have accumulated signifi-
cant amounts of sand in the lai:ge intestine may. pass. some of 
it in the fee.es. This sand may settle into the fingers of the 
rectal sleeve. 1'1nding sand that settles out with the sedimen-
tation test often indicates sand as a potential source of colic 
(Le., a sand colic). 
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UNDERS TANDING EQ UINE CC)l, IC 
MlclOblologlcol sampling (CUitures) 
~1icrobiological samples can be cultured to reveal bacterial 
organisms that might be associated with infectious causes of 
colic. Samples include abdominal fluid from abdominocente· 
sis and fecal material in cases of diarrhea that could be associ-
ated with specific bacteria such as Saltnonella, Clostrfdia, 
and o ther potential pathogenic bacteria. Intestinal biopsies 
and cultures of abdomi11al abscesses can also be sampled for 
culture and sensitivity. 
Elldoscop/c examination 
Endoscopic examination o.f the esophagus and the rectum 
can be performed r.o evaluate for the presence of obstruc-
tions, strictures, diverticulae (ab11ormal outpouchings of the 
gastrointestinal tract), tears or other perforations, and inflam· 
1nation and/o:r ulcers in association with a colic epiSode, per-
sistent or recurrent colic: epiS<)des, poor appetite, slow fet:d 
consumption, dysphagia (inability to bWallow and/or eat nor-
mally), straining, and retching. Endoscopic examination is also 
often used to monitor progress of healing of stomach ulcers. 
The endoscopic examination is not common in the evaluation 
of most classic cases of equine colic. The most common 
reason to pccfonn an endoscopic examination of a horse With 
t.-olic is to ev-.Uuate for the presence of gastric and, occasional-
ly, duodena.I ulcers as a cause of colic. Stomach ulcers are rela-
tively common and probably affect the majority of peJfor-
mance horses to some degree. Ulcers may also occur In the 
large Intestine. However, it is not possible to perfunn an endo-
scopic examination of a horse's large intestine because of the 
intestine's distance from the recru.m. Although duodena.I 
ulcers occur in horses, the duodenum is usually too far to 
reach with an e11doscope, except. in foals and small horses. 
DIAGNOSTIC IMAGING 
Diagnostic imaging modalities are used to help evaluate 
horses with col.le:. 'llJese n1odaHtles may include ulr.rasonog· 
Copyri~1led material 
Tii e Co li e E .ro 111 i noti o11 
r'aphy, radiology, nudear scintigraphy and con1puted comogra· 
phy, or magnetic resonance imaging. 
Ultrasound 
Ultrasound is by far the most common diagnostic imaging 
technique used in cbe colic examination. This non-invasive 
modality can be performed nearly an)'°'vbere because of the 
large number of portable machines no'v available. Use of uJ. 
trasound in evaluation of the horse's abdomen takes consid· 
erable veterinary experience. Even with a \•eterinarian's ex-
perience, the ultrasound machine has a number of inherent 
limitations. Depending on the ultr'.lSOund probe(s) used, the 
displayed inlage represencs an incomplete picture of the 
abdomen. Furthe.rmore, because a gas interface (an organ or 
space that is filled with gas) provides a barrier to ultrasound 
\vave penetration, horses with significant gas distension of 
the intestine ofien cannot be evaluated beyond the ~-urface of 
a gas-filled segment of intestine. 
Aorses with sigoificanr fluid-filled intestines can be identi· 
tied easily \vitb ultrasound provided the fluid-filled loops 
• 
use or ultrasound In diagnosing colic requires expertise. 
Copyrighted rT'":ttenal 
UNDERSTAND ING EQ UINE COLIC 
occur in areas the probe can penetrate. lntestinal motiliry and 
distension can be e\•aluated for both the large and small in· 
testine. The thickness of the inrestinal \vall can be evaluated 
aod measured. Suci1 evaluation n1ay provide added informa· 
tion about the presence of inflammation and edema in the in-
testinal wall. Certain rypes of colic may be diagnosed, or at 
least pre~w:nptively identified, using ulrrasound evaluation. 
They include nephrosplenic entrap1nent (see Chapter 3. in-
testinal displacement), inrussusception (see Chapter 3 Stran· 
gulating or nonstrangulating lesions), right dorsal colitis, 
some abdominal abscesses, some abdominal soft tissue 
masses, and others. The use of the uluasound machine often 
provides information oo clistension, filling, and appearance of 
specific areas such as the stomach, duodenwn, cecum, small 
colon, and rectum. It also can provide similar information for 
non-specific areas of the small intestine and large intestine. 
Radiogrophy 
Radiography, when used for abdominal problems in the 
horse, is probably most likely to involve imaging of the 
esophagus, possibly with tbe aid of a contrast agent such as 
barium. Contrast agents allow the dinici.an to evaluate for the 
presence of foreign bodies or masses io tbe intestio.es and for 
abnormal distensions (such as diverticulae) and ~trictures. 
Coot.cast radiography is probably most useful. for the evalua· 
tion of esophageal and rectal problems. The use of contrdSt 
radiography is expanded for foals because the entire 
abdomen can easily be cadiographed due to the foal 's &ize. 
Contrast radiography cao be peiformed with a fluoroscope 
(an X-ray machine that is capable of real-time imaging) to vi-
sualize contraSt n1aterial n1ovement in real time. However, tbe 
use of a fluoroscope is size·r~tricted and, tberefore, probably 
most practical for foals. Radiography of the adult horse's 
abdomen seldom yields useful results since the size of the 
adult abdomen precludes diagnostic films fron1 being ob-
tained, and the doses of radiation rcq11ircd are extremely 
Copyrigjl;.J,'(j material 
Tls t Co l ic E .romiuotion 
high. However, radiograpbs of the adult abdomen have beeo 
used ro help identify problems tbat stand out even on poody 
exposed films. These con ditions indude t:be idc:ntilk-atioo of 
sand in the large intestine and the p.re:sence of an enterolith 
(a sronc that bas fonned within the large inrestine). Contrast 
radiography on rare occasions might involve the vasculature 
rather than the intestines if there appears to be an indication 
of something such as an obstn1cted vessel. 
Nuclllar Sclnligtaphy, CT, and MRI 
The principle of nuclear scintigI"dphy Is the uptake of a ra· 
dloactive substance in metabolically active areas of bone or 
soft tissue where mere might be inflammation and remodel· 
ing. Tbe radioactive isotope is injected intO the horse intra· 
venously, and a gamma camera is uS(X! to •scan• the horse for 
r.tdioactive emissions from such sires. Areas of Jnflamrnation 
a.od infection also can be specifically and sensitively ideoti· 
tied by using nuclear scintigrdphy. Radioisotope may also be 
used to label white blood cells. \Vbite cells are taken out of 
blood taken from the horse and the radioactive isotope is 
•added" to label them. 1be white cells are th.en administered 
to !he horse,