Complexity of colic magnifies challenge of isolating its cause

Equine colic is "responsible for more deaths in horses than any disease group except old age." That's how Nathaniel A. White, DVM, MS, Dipl. ACVS, described the insidious nature of the condition in a 2005 presentation to the American Association of Equine Practitioners in Quebec.

White, Jean Ellen Shehan professor and director of the Marion duPont Scott Equine Medical Center at the Virginia-Maryland Regional College of Veterinary Medicine (VMRCVM), noted that, in a normal farm population, colic deaths are 0.7 deaths per 100 horse-years, a fatality rate of 6.7 percent, with fatalities due to stomach rupture, strangulating lesions or enteritis.

In a recent U.S. study of horses more than 30 days of age, 32.5 percent of deaths were from "unknown causes/all other causes," followed by old age (28.9 percent, a catch-all category), and then injury/trauma/wounds at 16.3 percent, followed by colic at 14.6 percent.

It has been estimated that there are 12,000 to 24,000 colic surgeries annually, or possibly as many as 2.7 per hour.

Surely equine colic is a serious and significantly prevalent disease.

The value of horses lost to colic in 1998, White stated, was more than $70 million, with a total cost to the industry during the year estimated at $144 million.

Understanding the cause/s of colic is difficult because of its complexity. It is related to several different diseases or conditions that result in various types or forms of colic, be it ileal impaction, gas distention/spasmodic colic or strangulation.

The cause may be as evident as grain overload or parasite infection. It is more complex when the entire GI tract is affected – the large colon is most commonly involved, followed by the small intestine, cecum and small colon, respectively – diseases or conditions that affect the gastrointestinal propulsive motility, which "depends on a complex interaction between neural, hormonal, vascular and neuromuscular pathways," states Judith Koenig, Dr. med vet, DVSc, DACVS, Ontario Veterinary College, University of Guelph. "Disruption of this intricate interaction leads to stasis of aboral movement of food material, or so-called ileus," Koenig notes.

Digesting possible causes

Noah Cohen, VMD, MPH, PhD, Dipl. ACVIM, professor of equine medicine at Texas A&M University, hypothesizes that people who confine horses in stables or barns under poor management practices "have altered the natural evolutionary existence of horses as grazers and herd-members. Changes appear to have had adverse physiological and behavioral consequences."

Have people inadvertently influenced the prevalence of this disease?

If so, what particular risk factors related to colic can be modified to possibly reduce the incidence of, or change the dynamic that may have tipped the scale in favor of colic?

It would be against Darwinian logic that the natural existence of horses in herds grazing open pastures would promote a disease "more responsible for deaths in horses than any disease group except for old age," or even at 14.6 percent.

There are several risk factors allied to the incidence of colic, but those that seem most directly associated with it would seem to be those that would directly impact the gut, i.e. water intake, feeding/food sources and pasture. Management practices are another point of interest.

Drinking water

Some studies have noted the association of drinking water and colic risk. Access of horses to ponds, as opposed to watering with buckets, tanks or troughs, has shown benefit. But access to ponds might be linked to exposure to larger pastures, rather than an effect of the source of water, per se. Likewise, the link between colic and horses in barns, where they are watered with buckets, may be the occasional lack of water due to empty buckets, water unavailability, rather than the manner in which water is dispensed.

Access to fresh, clean water might be the key. Cohen notes, "Provision of an adequate amount of water that is fresh, palatable and potable is important."

A look at feeding practices

In three separate studies with large groups of horses examined by private practitioners, Cohen and colleagues studied the association of feed and feeding practices with colic.

In one study of more than 1,600 animals, 821 were treated for colic, while an equal number had other conditions. The types of concentrates and hays fed to horses with colic were similar to that of the controls – oats to roughly half of each group; a 12 percent sweet feed to about 30 percent of each group; and a 14 percent sweet feed to approximately 17 percent of each group.

Coastal Bermuda hay was fed to an equal amount of each group; about 82 percent of colic (672/821) and control (669/821) animals; alfalfa to about 32 percent of each group; and about 9.5 percent of each group were fed other hays. Therefore, there were no significant differences or alliance with any feed to colic or non-colic horses.

What was significant was change in diet.

"History of any recent change in diet was determined for 1,607 horses (807 with colic and 800 control horses), and a recent change in diet was found to be significantly (P <.0001) greater among horses with colic (19.7 percent) than among control horses (4.9 percent)," Cohen explains.

In a subsequent study (1,030 pairs of colic and control horses), also done at Texas A&M, Cohen and colleagues found that "colic horses were significantly less likely to have been fed on pasture than were control horses."

Of horses fed different feeds, colic (532) and control (563) were fed sweet feed; fed oats, colic (411), control (386); fed pelleted concentrate, colic (193), control (183); a mixture of sweet feed and pellets, colic (46), control (38); fed corn, colic (20), control (22); and those fed extruded feed, colic (9), control (12). Again there were no differences due to concentrate type that was fed.

Similarly for type of hay fed: There were no differences between the colic and control groups – alfalfa hay, colic (204), control (201); coastal or Bermuda grass hay, colic (753), control (736).

Like the previous study, diet change again was significant, but of all the changes – concentrate to hay, one grain to another and one hay to another, changes in amounts of hay and/or grain – "only change of hay was significantly associated with colic."

Of dietary supplements fed (vitamins, minerals, proteins, fats), none of them, nor their amount, was associated with colic.

Another study by Cohen and colleagues of 182 matched pairs of colic and control horses showed similar results. Of 165 horses fed sweet feed, about 50 percent experienced colic; those fed pellets, there was no difference in colic incidence; for those fed oats (136), 72 were colic cases, 64 control, and of those fed other grain, 30 horses, half were with and without colic.

Feeding >2.7 kg oats was allied to increased colic incidence. Change in concentrate/grain fed was again a source of colic.

"A change in the type of grain or concentrate fed during the two weeks prior to examination (e,g., from pellets to sweet feed) significantly increased the risk of colic." The study also stated, "Horses with no grain intake appeared to be protected from colic, compared to those fed grain or concentrate on a daily basis."

Of 244 horses fed coastal or Bermuda grass hay, an equal number were colic and non-colic cases; alfalfa hay, also even. It was assumed that 6 flakes of hay per day was considered free-choice, and it was shown that consuming >2 flakes per day of hay other than coastal, Bermuda or alfalfa was associated with increased incidence of colic. Switching to a different type of hay was not found to be associated with colic, though horses that were recently fed a change in amount of hay was.

Various aspects of feed and feeding have been linked with increased colic risk.

White adds that course roughage with low digestibility or particularly course fiber can cause impaction colic, while horses fed Bermuda grass have an increased risk of ileal impaction. Grain overload increases colic risk. Overfeeding on lush grass, especially clover, may cause tympany; alfalfa hay, reduced hay quality/digestibility and feeding from round bales have been implicated as well.

Changes in feeding practices, i.e. a sudden increase in grain, changes in type of hay or grain, or greater than 5-kg concentrate per horse per day, have been linked to increased colic risk, as well as feeding of pelleted feeds and sweet feeds, compared to no grain at all.

Lower in fiber, grain diets have been shown to decrease colon water content, due to lesser ability to bind water. Grain also is said to increase gut gas production, predisposing to tympany, distention and displacements.

What seems basic to these feeding practices and association with colic is dietary change as well as deviation from feeding the horse because the animal would naturally graze in open pasture. In some cases, it was noted that feeding grain soon after being brought in from pasture increased risk, while keeping horses out on pasture while feeding grain decreased risk.

While one can properly feed horses by incorporating concentrate to its diet, the basic need for about 1.5-2.0 percent roughage is important. Nibbling eating behavior on lush pasture, and without abrupt dietary changes, if hay is also available, decreases the risk.

In some studies, feeding small amounts of grain at frequent intervals has been reported to decrease the large-colon water shifts. Though one study showed that feeding grain more than twice daily was related to increased colic risk, the total amount of grain consumed may have been the culprit rather than the frequency of feeding.

Pasture

Several studies have demonstrated that access to pasture and increased opportunity for grazing are related to reduced risk of colic, while one study associated increased hours of stabling with increased risk.

The major concern associated with pasture and increased risk of colic is grass sickness or overindulgence of fresh lush spring pasture.

As opposed to various time periods turned out to pasture, it was shown that spending 100 percent of time in a stall was significantly associated with increased risk of colic (in one study), and that horses having less access to pasture were at risk to colic.

Management practices

Confinement has been shown to be both a positive and negative influence on colic risk. According to White, a VMRCVM study showed that housing and confinement on farms in the area were not a colic risk factor, while other studies showed that increased confinement and reduced activity may lead to higher risk of cecal and large-colon impaction.

Looking forward

Cohen proposes that even with the epidemiological information already considered, new statistical and epidemiological models "are needed to address the many deficiencies in our knowledge about the causes of colic in horses.

"Statistical models that might be applied include principal-components analysis and related methods or neural networks, which may provide a method for better defining the simultaneous contributions of groups of variables contributing to colic, the complex pathways by which predisposing factors may result in colic, or both," Cohen says.

"Epidemiological models other than the risk-factor-identification approach that is currently dominant, or more communal-based approaches, may be needed," Cohen adds.

While the majority of clinical cases of colic are based in the general horse population, most of the studies investigating the possible cause(s) have been conducted at universities and teaching hospitals. It's another concern, Cohen adds, because results from such studies may have limited applicability to the general horse population.

Information is needed from private-practice clinicians, which may be more representative of horses and colic incidence. "Collecting reliable data from practitioners selected in an unbiased manner could provide extremely valuable information," Cohen suggests.

"We will never eliminate colic in horses, but I do believe some can be reduced by better management. And more data are needed to establish practices and circumstances that are risky or salutary," Cohen adds. "This will require both funding and effort."

Maybe there is an answer somewhere in modifying the practices associated with colic risk – practices that essentially have changed the horse's environment from its once range-pasture existence.

That is not to suggest that people can't keep horses as they do, but maybe we can find out what is being done to drive the statistics toward increased colic incidence. "To me," Cohen explains, "the challenge is going to be how we manage the health of horses, given the ineluctable changes that will occur in the future — less grazing, less turnout, reductions in hay production with demands for land, changes in grain farming, greater density, more transport, etc. This is what we need to be thinking about if we want to be ahead of the curve."

Photo 1: Cecocolic intussuception that is partially reduced in surgery. Photo 2: Jejunum that was entrapped in the scrotum of a stallion. Notice the devitalized jejunum after the abdomen was explored. Photo 4: A pedunculated lipoma strangulating about 1 foot of jejunum, which is devitalized. Photo 3: This shows performance of a jejunocecal anastomosis with stapling equipment after resection of devitalized ileum. Photo 4: A pedunculated lipoma strangulating about 1 foot of jejunum, which is devitalized.

Ed Kane has 25 years' experience as researcher and consultant in animal nutrition. He is an author and editor on nutrition, physiology and veterinary medicine with a background in horses, pets and livestock. Kane is based in Seattle.