Seasonal Horse Manure Changes

A veterinarian answers a reader’s question on why some horses have runny manure certain times of the year.

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Seasonal Horse Manure Changes
A change in a horse's fecal character can indicate anything from internal parasites to infectious disease. | Photo: iStock

Q: Why do some horses have seasonal runny manure? Like clockwork every late fall, one of my old guys starts to have regularly runny poop. And every spring around May 1, his manure goes back to normal. He eats the same type of hay year-round, the same grain, in the same area. It does not seem to relate to being on grass. He’s been looked at by several vets with no conclusion. I’ve tried everything from probiotics, prebiotics, Biosponge, and Sand Clear to deworming, low-starch feed, chopped hay, and soaked hay pellets. What else can I do?–Maureen, Wisconsin

A: This is a question that equine veterinarians receive from time to time, often about older horses that may appear to be healthy in many ways. I have listed my approach to such cases so you can learn why some horses might have changes in their fecal character.

If your horse experiences a change in fecal character resulting in soft (cow pie) or watery feces, first see if you can determine the cause. If there is no apparent reason for the change in feces, such as a recent alteration in diet (e.g., rapid switch to moist grass or legume hay), then talk to your veterinarian. He or she might perform an overall health check that includes a complete physical examination and blood collection for a complete blood count and serum chemistry analysis. The physical examination will include an assessment of hydration status, a temperature check, and a careful listen (auscultation) to the heart, lungs, and gastrointestinal tract. This part of the examination will allow the veterinarian to determine if any other organ system is abnormal or if the problem is confined to the gastrointestinal tract. We can generally detect primary gastrointestinal disease on physical examination in combination with a fecal analysis. Perform periodic fecal exams to determine parasite fecal egg count. Based on this analysis, you and your veterinarian can design a deworming program. Also float feces for sand to determine if sand may be involved with the altered fecal character.

Additional investigations often include an oral exam to determine the status of the horses’ teeth (dentition). In some instances a change in fecal water content results from an increase in fiber (hay) particle size, due to altered dentition that we can improve or correct with routine dental floatation. Specifically, when elderly horses have poor dentition (wave mouth with or without sharp points and hooks), they can experience difficulty breaking fiber down into a small enough particle size for digestion. In such cases, increased particle size leads to increased water being drawn into the intestinal lumen, which results in feces with a higher moisture content—the soft feces or diarrhea you see.

In some cases the change in fecal character may result from a primary gastrointestinal pathogen, such as bacterial or viral challenge. Your veterinarian will be best able to determine if any of these organisms may be present. Most commonly, if the horse has an infectious disease, he will appear lethargic, have a fever (possibly intermittent), and may have a change in appetite. In cases where the veterinarian finds a change in complete blood count or protein concentration, he or she can perform diagnostic testing, such as bacterial culture and/or polymerase chain reaction (PCR) testing, to detect any microorganisms present.

In some instances there is no primary health problem to account for intermittent loose feces or diarrhea. Working with your veterinarian will help you ensure there is no other cause for the increased fecal water content. Although these cases can be challenging, as long as the horse is able to maintain hydration (by consuming plenty of water) and electrolyte status, there is no major health problem caused by the passage of intermittent loose stool.


Written by:

Elizabeth Davis, DVM, PhD, Dipl. ACVIM, is a professor and section head of equine medicine and surgery at Kansas State University’s College of Veterinary Medicine. She is also the Associate Dean of Clinical Programs. Her research focuses on immunology and effective vaccination strategies and clinical pharmacology.

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