Colic in horses encompasses symptoms of general abdominal discomfort rather than an actual diagnosis.
Frequently an owner will notice a colicky horse at feeding time when the horse shows no interest in feed, may be standing stretched out, pawing the ground or kicking, bending and staring or biting at the abdomen, or lying down and rolling.
There have been few study protocols inducing colic in horses. For this reason, studying cause and treatment is very difficult.
However, a number of typical types of colic have been documented including impaction, spasmodic, intestinal twist, and enteritis. Intestinal twist or strangulation is a serious condition in which the gastrointestinal tract becomes blocked, slowing or stopping the blood supply and digesta flow through the gastrointestinal tract.
Strangulating lipoma is a condition in which a benign fatty mass and the thin stalk that it is suspended from wrap around a section of intestine similar to a bolo. Older horses, especially geldings, seem to be more prone to this type of colic.
The cause of intestinal twist is not clear, but does not appear to be associated with a horse rolling as was once thought. Surgical intervention in gut strangulation is required, with the best success rates seen in surgeries performed early in the progression of the colic.
Impaction and spasmodic colics are generally associated with dietary factors. Diet related colics represent the greatest proportion of diagnosed colic cases (Cohen et al., 1995).
Impaction colic
Impaction colic is caused by blockage of the intestine by material such as normal ingesta, gas, or enteroliths (stones that form around ingested twine, sand, pebbles or other foreign material similar to the way a pearl forms in an oyster from a foreign irritant). In the case of impaction colic, material behind the impaction can cause distention of the intestine, which contributes to the pain the horse feels.
Impactions can occur for a variety of reasons including poor mastication of feedstuffs, lack of drinking water, parasite infestation, poor quality hay or rapid diet changes (King, 1999; Ramey, 1996). In some cases poor quality forage (high lignification, long stem) or very fine roughage such as coastal Bermuda grass has been implicated with colic incidence (Keen and Coates-Markle, 2005; Ramey, 1996). Large colon impaction was the most frequently encountered type of chronic colic (30% of all colic with symptoms lasting three days or more) observed in a British study (Mair and Hillyer, 1997).
In this study, cecal impactions were observed in less than 3% of the cases. Cohen and coworkers found colonic impaction to represent 20.7% and 16.5% of the clinical colic cases observed by veterinarians in Texas (Cohen et al., 1995; Hudson et al., 2001). Ileal and cecal impaction was diagnosed in approximately 3.3% of colic cases (Cohen et al., 1995). A follow-up to the 1995 study indicated that a change in diet (specifically hay) was associated with colic (Cohen et al., 1999). This group also implicated lower quality hay as a possible link to colonic impaction.
Later, a study confirmed these results by examining 364 horses and finding that dietary changes such as a different batch of hay, different grain or concentrate and decreased availability to pasture increased the risk of colic (Hudson et al., 2001).
The cecum and colon of the horse is considered the major site for fiber digestion (King, 1999; Pagan, 1991). Medina and coworkers (2001) examined the effects of Yea- Sacc®1026 viable yeast culture on poor quality forage disappearance in vitro when cecal and colonic fluid samples were taken from horses fed either high fiber or high starch diets. Regardless of whether the horses were fed the starch or fiber-based diet, in vitro disappearance of the lignified fiber was greater in cultures prepared from horses receiving Yea-Sacc®1026than unsupplemented horses. These data imply that Yea-Sacc®1026- supplemented horses could adapt to dietary changes more readily than those not receiving the supplement.
Fiber degrading bacteria prefer a pH near neutrality. In fact, Stewart (1977) found that fiber digestion decreases dramatically as the pH drops. The author noted a 50% decrease in cellulose degradation when bacteria exist in an environment at pH 6.5 compared to pH 7.0. Fiber degradation was brought to a standstill at pH below 6.0.
Moore and Newman (1994) found that the cecal pH was higher overall when Yea-Sacc®1026was fed to ponies (6.62 vs. 6.52 for unsupplemented ponies; P<0.05). These results were confirmed in a later study that found average cecal pH to be greater (7.01 vs. 6.85; P<0.05), at 4, 6, and 8 hrs post-feeding with Yea-Sacc®1026supplementation of a high starch diet (Medina et al., 2002). A 0.9 pH unit increase was also observed in the colon (P>0.05). The average cecal and colonic lactic acid concentrations in horses fed the high starch diet was also lower when the animals were supplemented with Yea-Sacc®1026.
Maintenance of a higher intestinal pH may therefore increase fiber digestion which will improve feed efficiency and maintain flow of digesta and may aid in preventing feedrelated impactions (Moore and Newman, 1994). Indeed, studies have shown increased digestibility of dry matter (DM), magnesium, phosphorus and potassium (Glade and Sist, 1988; Pagan, 1989) in equine diets supplemented with Yea-Sacc®1026.
Enterolith impaction colic
The minerals that comprise most enteroliths are a combination of magnesium, phosphorus and ammonium (also called struvite). The above mentioned studies document improved digestibility of magnesium and phosphorus; and Medina et al. (2002) demonstrated lower ammonia concentrations in the ceca of Yea-Sacc®1026supplemented horses. With these collective data, it is tempting to attempt to make the assumption that enterolith production may therefore be decreased with Yea-Sacc®1026supplementation.
However, researchers at UC Davis believe that enterolith formation is multifactorial with diet, environment and genetic factors being involved (Anon, 2004), so while Yea-Sacc®1026may affect one parameter, other factors may be present in sufficient quantity to cause enterolith production. Some may also question the value of a product that has been shown to increase gut pH since current recommendations are to add vinegar and/or increase the amount of grain in the diet to help prevent enteroliths. This is because the above mentioned minerals tend to precipitate at alkaline pH values.
However, Medina et al. (2002) further discovered that in high fiber diets that tended to increase the alkalinity of the gastrointestinal tract, Yea-Sacc®1026supplemented horses had numerically (but not statistically) lower pH values. These data seem to indicate that moderating the pH of the intestinal tract is associated with Yea-Sacc®1026supplementation rather than providing alkalinity.
It is also prudent to examine thoroughly the relative on-farm risk factors before beginning a program of increased concentrate and/or added vinegar to the feed to attempt to prevent enterolith formation. British studies indicate enterolith incidence at less than 1% of all colics (Mair and Hillyer, 1997).
A Texas study found the incidence of colonic impaction ‘associated with sand’ at 2.9% of the total number of horses diagnosed with colic (Cohen et al., 1995). Enterolith formation seems to have a higher frequency in California, Florida and Indiana (King, 1999; Ramey, 1996). When grains and concentrates were fed at rates greater than 2.7 kg/day (6 lb), Hudson and colleagues (2001) found there was a greater risk of colic.
Associations of enterolith formation with feeding alfalfa hay have also been made due to the relatively high magnesium and protein content and the apparent buffering capacity of this type of forage.
Spasmodic colic
This type of colic presents as increased intestinal contractions or spasms. With spasmodic colic, the horse may visibly contort from the pain. A Texas study found this to be the most prevalent colic type (29%) while the second highest incidence type was impaction (19.5%; Cohen et al., 1995).
Spasmodic colic is primarily caused by rapid microbial fermentation of concentrates or lush pasture material. These feedstuffs contain a high percentage of relatively simple sugars that are quickly digested by bacteria that produce gas and/or lactic acid from these sugars. The buildup of gases can cause intestinal stretching leading to discomfort for the horse.
In studies using in vitro cecal simulating systems, Newman and Spring (1993) observed decreased gas production in cecal simulators receiving feed with Yea-Sacc®1026at 6 and 12 hr post-feeding compared to simulators receiving the same diet without the yeast culture.
Feed particle size may also play a role in digestive upset. Studies in equids have shown that small particle feed flows relatively quickly through the cecum, but remains longer in the colon (Drogoul et al., 2000a; b). The rapid rate of passage may allow the small particles to by-pass normal starch degradation with more starch reaching the microbial fermentation sites.
Upon further investigation, de Fombelle et al. (2001) demonstrated that the colon appears to be the site in the gastrointestinal tract that would be adversely affected by overfeeding rapidly fermentable concentrates such as barley. In this study, concentrations of lactobacilli and streptococci in the large intestine increased significantly following a dramatic diet change from 100% hay to a 50:50 (hay:barley) diet.
Summary
Because colic is defined as abdominal discomfort and can be caused by a number of factors, some of which have not been defined, an all-encompassing therapeutic or prophylactic regime is not possible. Surgical intervention is required for intestinal twists and strangulation. However, it is generally accepted that a stabilized intestinal environment can increase digestibility and keep microbial fermentation of feedstuffs properly functioning. Yea-Sacc®1026has been shown in a number of studies to moderate intestinal pH, improve fiber digestion and positively impact mineral absorption. These data suggest that Yea-Sacc®1026may serve as an aid in preventing certain predisposing factors associated with colic.
References
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