Understanding Equine Endotoxemia, One of the Leading Causes of Horse Mortality.

When a horse's bowel system is out of balance, this can result in the release of endotoxins. Endotoxemia is the leading cause of equine death, being a major component in gastrointestinal disorders such as colic and neonatal foal septicemia.

Endotoxins are normally present in the horse's bowel. A normal, healthy equine bowel harbors vast quantities of micro-organisms that not only help the horse's gut to break down fibrous feeds, but helps to limit the overgrowth of disease-carrying bacteria. More specifically, endotoxins are actually the byproduct of, "Gram-negative bacteria," which release a portion of their cell walls as they multiply.

Newborn Foals Are Vulnerable
Endotoxemia can quickly take over a newborn foal*

Normally, these bacteria and their byproducts are prevented from migrating outside of the horse's bowel by a complex intestinal barrier. The horse's bowel is lined with a mucus-secreting membrane lining designed to keep endotoxins in place. This membrane works in concert with enzyme and antibody secretions, also designed to keep endotoxins where they belong. Small, but normal amounts of endotoxins that manage to cross the mucosal barrier into the liver are attacked by specialized immune cells.

Sometimes the bowel's environment is altered enough to allow too many "Gram negative bacteria," to die off at once, resulting in an endotoxin overload. Or, there may be an injury to the horse's intestinal barrier caused by reduced blood flow, gastrointestinal disease or surgery. Additionally, non intestine related issues such as bloodstream bacteria overload (septicemia) or post-foaling placenta expulsion issues can play a role, allowing excessive amounts of endotoxins to be absorbed by the horse's central circulation. Even antiobiotics can impact gastrointestinal populations negatively, allowing some disease related pathogens to flourish.

From Initial Inflammation to Potentially Life Threatening, Endotoxic Shock.

Once a horse's protective mechanisms have been overwhelmed, the horse may appear to experience clinical symptoms such as pain, intestinal shutdown, rapid heart and respiratory rates, sweating, dehydration, anxiety and fever. The horse may lapse into endotoxic shock, which may be life threatening.

What to Do During an Endotoxic Crisis.

Particularly with colic, the duration of the endotoxic crisis is critical. Many medical treatments only provide temporary relief in the more severe cases. A horse suffering with severe or recurring pain despite medication with painkillers or mild sedatives should be immediately hauled to a properly equipped clinic where medical therapy and continued monitoring can be implemented. It's important to A. catch the problem early and B. address the problem surgically to restore bowel function. Prompt treatment not only inhibits inflammatory impact, but gets the horse back on track, that much faster. Be advised that if the intestinal disruption is strictly inflammatory in nature, such as with colitis inflammatory conditions or enteritis, medical therapy, rather than surgery may be the correct choice.

 

Endotoxins In The Stable Environment.

Inflammatory airway disease can be impacted by a number of issues such as: stable ventilation, bedding, feed quality, endotoxins in the environment and respirable particulates, among others. Horse manure typically contains high concentrations of "Gram-negative bacteria," making endotoxin a daily part of the horse's external environment. Inhaling endotoxin along with dust can induce airway inflammation and exacerbate equine heaves. Horses kept stabled may breathe as much as 8 times the amount of endotoxin as that experienced by pastured horses.

In an ideal world, stabled horses should be removed from stalls when they're mucked out or when the aisleways are swept. Additionally, owners are advised to steam or soak hay to minimize the inhalation of endotoxins by horses considered at risk for heaves. Soaked hay should be fed immediately, otherwise it may become a haven for bacterial proliferation, making it another endotoxin hotbed.

Suggested Endotoxin Treatments

As previously mentioned, averting inflammation and supporting the horse's cardiovascular system via aggressive medical treatment is critical. In the best of circumstances, your veterinarian will prevent endotoxin from penetrating the horse's circulation system to begin with. Waiting until the horse is seriously ill is not desirable. By neutralizing endotoxin, it can be prevented from binding to white blood cells, allowing for improved blood pressure, the blocking of a continuing inflammatory response and its potential consequences.

Horses with excessive endotoxin levels are often treated via intravenous fluid therapy. While the horse may not be suffering from dehydration, IV fluids increase the blood pressure levels around the horse's brain and heart. Your vet may also utilize Hetastarch, a plasma substitute, in conjunction with the IV fluids. Some vets also use the anticoagulant Heparin to help discourage secondary problems such as laminitis.

Administering Non-Steroidal, Anti-Inflammatory Drugs

A popular therapy used by many vets is the administration of Flunixin Meglumine, via IV. It is considered a mainstay treatment for endotoxemia and colic. While once considered a miracle treatment, be advised that Flunixin can also mask further deterioration in approximately five to ten percent of horses known to have experienced intestinal injury such as twisted intestines. Flunixin has also been known to negatively impact equine kidney and gut health. Some veterinarians may utilize lidocaine, post operatively, as it can help reverse Flunixin related gut healing delays.

Endotoxin Binding Therapy

Low dose intravenous administration of the antibiotic Polymyxin B can help to bind endotoxin, preventing it from interacting with the horse's white blood cells. It must be administered in a timely fashion, before endotoxin can cross the intestinal barrier. When treating horses with intestinal twists, surgeons often adminster Polymyxin B prior to untwisting the bowel. There are also anti-endotoxin serums and plasmas available to bind endotoxin. Renowned for their success in improving equine survival rates, they also must be administered as early as possible.

Potential New Treatments For Endotoxemia

Among medications currently being tested in the treatment of endotoxemia are ethyl pyruvate, phenylmethimazole, pentoxifylline and ketamine. Inhibiting inflammatory response and providing sufficient cardiovascular support are key to managing equine endotoxemia. Ideally, the best therapy is prevention. This means avoiding sudden changes in feed, maintaining adequate fiber levels and feeding smaller amounts, more frequently. Being aware of the kinds of conditions that could trigger endotoxemia and treating them aggressively can also play a major role in minimizing the potential consequences of this condition.

 *Image courtesy of Dollar Photo Club