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.
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."