Inside Information: 10 Signs of Internal Illness in Horses

Horses can give us plenty of cues when they’re dealing with early illness. To help you recognize them and intervene accordingly, we’ve put together this 10-point list of warning signs.
Please login

No account yet? Register


10 Signs of Internal Illness in Horses
Signs as subtle as standing quietly in the barn, refusing to eat hay or socialize with herdmates, can point to internal illness. | Photo: iStock

I walked out to check on my two horses about an hour before sunset. Solstice was in the paddock, eating hay, snorting contentedly, and swishing his tail. When I walked up to the fence, he perked his ears and looked at me with bright, cheerful eyes.

But Sabrina stood quietly in the run-in shed. She saw me approach, poked her head out, blinked, and sighed. She ambled out of the barn toward me, put her head over the fence, and waited for me to stroke her face.

Wait. She wanted her face stroked? Sabrina was not well.

As much as Solstice loves to be cuddled like a golden retriever puppy, his dam, Sabrina, acts like she has too much dignity for public displays of affection. She’d rather be chasing Solstice from every hay pile and pinning her ears when he tries to steal a bite. The last thing she’d do is hang out in the barn watching him eat her hay and then come to me for a scratch on the head.

Two hours later Sabrina was on the ground, curling her lip and groaning. I’d already called her veterinarian, who determined from my description of her symptoms that she was colicking. Fortunately, with my vet’s help, Sabrina’s colic resolved within a few hours.

Horses can give us plenty of cues when they’re dealing with early illness. The problem is they don’t; horses don’t like to show that they’re sick.

“They’re a prey species, so hiding any evidence of illness is a survival technique,” says Elizabeth Davis, DVM, PhD, Dipl. ACVIM, professor and head of the department of clinical sciences at Kansas State University’s Veterinary Health Center, in Manhattan.

But they do give subtle signs, like Sabrina’s uncharacteristic affection or her standing quietly in the barn or not eating hay. To help you recognize them and intervene accordingly, we’ve put together this 10-point list of warning signs.

1. Diminished or absent appetite

Has your horse suddenly become picky about or even completely uninterested in his food? That’s a significant sign of brewing illness, our sources say.

“A change in appetite, whether for grain or hay or both, is a big indicator to me that something isn’t quite right,” says Davis. “Whereas he used to take 15 minutes to clean up his bucket of concentrates, now it might take 45 minutes with some breaks to walk around a bit. Or he won’t eat hay as vigorously and will get picky about it.”

Appetite changes could indicate gastrointestinal upsets such as colic. In fact, waning interest in food can signal a wide variety of internal illnesses beyond the GI system, says Kari Bevevino, DVM, of Roaring Fork Equine Medical Center in Glenwood Springs, Colorado.

“This is among the most important signs of disease in various systems of the body,” she says.

2. Diarrhea

Any change in poop production is worth monitoring. But diarrhea, in particular, deserves special attention, says Bevevino. “Diarrhea can go from not-too-bad to very bad in a very short period of time, and early intervention is beneficial to both the horse and the veterinarian treating him,” she says. 

An infectious disease—which can cause severe illness or death and can also spread to other horses—is the most alarming possible cause, Bevevino says. Salmonella and Clostridium bacteria, for instance, cause diarrhea-related infections with varying levels of clinical signs.

“Some horses remain bright and alert while others develop very severe disease,” she says. Rapid treatment can ease discomfort, improve chances for recovery, and help the veterinarian and horse owner control disease spread.

Other causes of diarrhea include sand accumulation in the colon, inflammatory bowel disease, and, less commonly, cancer, she adds. Regardless of the cause, diarrhea can lead to rapid dehydration and electrolyte losses, sometimes requiring “pretty intensive therapy,” Bevevino says. 

Inside Information: 10 Signs of Internal Illness in Horses
A horse that's lethargic and stays separate from the group might be shoing early signs of sickness. | Photo: iStock

3. Lethargy, uncharacteristic calm or inactivity, and separation from the group

Horses should maintain a consistent activity level and keep up with the herd, our sources say. “A sick horse might stand off by himself and stay quiet,” Bevevino says. “By quiet, I mean he’ll hang his head a little lower, hold his ears a little less perked up than usual, and not have his eyes quite as wide and bright
as usual.”

You might also notice subtle lethargy, adds Davis. “Under saddle he might need a little extra encouragement to get going, and he might run out of gas a little sooner,” she says. “Or the pasture pet suddenly isn’t keeping up with the herdmates.”

4. Unusual Behavior

When caregivers pay attention to their horses and observe what’s normal for each, they’ll pick up more easily on what’s not normal, says Davis.

“There are certainly variations on an individual basis, so it’s important for people to see the horses at least a couple of times a day to get to know them,” she says.

Casual observers might miss the subtle red flags. “For example, the very social horse that’s normally looking in your pockets for a treat is now standing back with his head down,” she says. “If you’re really in tune, you’ll know when they’re telling you that something’s off.”

5. Fever

Body temperature is an objective measurement—meaning it has a numerical value—but for it to have significance, you must recognize when to take it.

“You usually wouldn’t know a horse has a fever just by looking at him or even touching him,” Davis says. “Sometimes you can see subtle signs, like patchy sweating or faster-than-usual breathing, but those don’t always occur.”

Keep a digital thermometer—one from any drugstore will do—on hand, and learn to perform a rectal temperature check, Bevevino says. If the temperature is above 101.5 degrees Fahrenheit in an adult horse, chances are you’ve got a problem. Know that environmental factors such as extreme heat, however, could push the critical temperature limit up to 102 degrees.

6. Other altered vital signs

In addition to body temperature, uncharacteristic respiratory rate and heart rate could indicate impending illness, Bevevino says. You can use a stethoscope to take these measurements, but it’s not necessary.

“Count the number of breaths (with your ear up to the horse’s nose or chest) in 15 seconds, and multiply that by four to get the rate per minute,” she says. “Most healthy horses at rest should have a rate below 20 to 24 breaths per minute.”

You can take the horse’s pulse along certain blood vessels, such as those in the pastern or under the jaw. Count the number of beats you feel in 60 seconds, and compare that to the healthy ­average—around 28 to 44 beats per minute in a resting adult horse.

Keep in mind, though, that individual horses’ vitals vary, so familiarize yourself with what’s normal for your horse when he’s healthy.

7. Weight loss and change in body condition

Illness can take its toll on a body, causing gradually visible signs, say our sources. “With an underlying illness it can get easier to see the ribs,” Davis says. “That could be true weight loss, or it could be lost muscle mass, especially over the topline, giving the appearance of weight loss.”

This kind of muscle atrophy coincides with illness primarily due to protein ­metabolism issues, she explains.

Because these appear over time, they might be more difficult for owners to detect because they see the horse regularly, says Bevevino. Soliciting an outsider’s view can help, but an even more useful tool is photography.

“One of the best monitoring devices we have is the camera in our phones,” she says. “Take regular photos from the same angle and lighting to keep track of your horse’s changes in body condition.”

8. Change in coat quality

Coat issues are usually easier to detect in spring and summer, when horses should shed out well and have slick, shiny coats, says Davis. But problems can be visible in the fall and winter, too.

“Regardless of season, if the coat looks a little rough or dull, or if there’s hair loss or thinning compared to previous years, those are signs that something’s not quite right,” she says.

Metabolic disorders such as pituitary pars intermedia dysfunction (formerly known as equine Cushing’s disease) can cause coat problems—often a lack of shedding and elongated (guard) hairs, as well as patchiness or other unusual patterns. Don’t ignore any coat issues, because they can be related to a variety of internal illnesses.

“Modifications in the coat are a huge sign for me,” Davis says. Because hair quality is related to nutritional status, coat changes are likely to reflect changes in appetite or nutrient absorption ability.

Gastric ulcers are a common culprit for poor coat quality,” she says. “They’re just not getting the nutrients they need, and their overall health status declines because of those ulcers.”

9. Change in bowel habits

Fecal character, consistency, and overall output should remain fairly constant, says Davis. “If their diet is consistent, they should be passing the same type and amount of material every day,” she says.

Be observant when cleaning the stall or walking around the paddock. “If you don’t find any feces in the stall, that’s not normal and could suggest an impaction,” she says. “But if things are moving too quickly, causing frequent or soft feces, that could mean a disruption in the  gastrointestinal tract’s relatively fragile microflora.”

Short-lived changes might be normal, resulting from stressful events such as separation from other horses or transport. But changes that last hours or days could represent parasite burdens, reactions to antibiotics, or other gastrointestinal issues. In severe episodes horses’ bodies might absorb bacterial byproducts in the intestines and develop a serious condition called endotoxemia, which often requires management using intravenous fluids and anti-inflammatories, Davis says.

10. A gut feeling something’s wrong

Sometimes your intuition is the earliest indication of illness. You know your horse, and something is telling you he’s feeling “off.”

Even if the subtle changes are difficult to describe, our sources say these observations are important to report to veterinarians. That’s because, for all their scientific knowledge, they don’t usually know your horse as well as you do.

“If you’re worried, I’m worried,” Bevevino says. “Horses are tough and tend to mask the severity of their disease, but a lot of times they can’t fool a really in-tune handler.”

Testing and Treatment

Subtle signs of illness don’t usually point to specific diseases. Your horse might be signaling that he has any of a number of conditions ranging from liver disease to infection, pneumonia to colic, because so many of these cause similar early signs. Instead of waiting for more obvious issues, call your veterinarian.

“If the condition seems to be progressing slowly, it may be okay to schedule an appointment for in a few days’ time,” says Bevevino. “But if the signs seem acute (sudden in onset) or progress rapidly, your vet should probably come immediately, because even early signs can mean serious issues and, of course, early treatment is always preferred.”

Your vet might not know what he or she is treating initially, but a thorough examination will help: palpating different body parts, including the limbs, listening to heart, lung, and bowel sounds, checking mucous membranes, and assessing hydration status, always looking for signs of discomfort and inflammation, says Davis. A general blood test can reveal abnormal blood parameters that might point to the affected body system. A urinalysis might provide critical information about kidney function and metabolism.

Ultrasound allows the veterinarian to check vital organs such as the lungs and liver, says Bevevino. If the horse is hospitalized, high-quality radiography can allow the vet to check for issues such as gastrointestinal and pulmonary (lung) diseases.

If your veterinarian suspects an infectious cause, he or she might run a polymerase chain reaction (PCR) test on the appropriate sample—whether blood, feces, tracheal wash, nasal discharge—to see if the DNA for the agent is present and target treatment, she says.

To check for inflammation, your veterinarian might test for protein markers of acute inflammation, such as serum amyloid A (SAA). “We might do the test one day and then repeat it in a day or two,” Bevevino says. “That way, we can determine if inflammation is a component of the disease and, if present, is it improving, staying the same, or worsening? It’s something we have in our arsenal to not only evaluate but monitor response or lack of response to treatment.”

Specific treatment depends on what diagnostic testing reveals, our sources say. But in the meantime, most horses benefit from supportive care such as intravenous fluids, anti-inflammatories, and stabling in a calm, comfortable environment.

Take-Home Message

Recognizing illness in its earliest phases can lead to targeted treatment that can hasten healing and increase a horse’s chances of recovery. By learning to pick up on the earliest signs of disease, handlers can get their horses the intervention they need faster.


Written by:

Passionate about horses and science from the time she was riding her first Shetland Pony in Texas, Christa Lesté-Lasserre writes about scientific research that contributes to a better understanding of all equids. After undergrad studies in science, journalism, and literature, she received a master’s degree in creative writing. Now based in France, she aims to present the most fascinating aspect of equine science: the story it creates. Follow Lesté-Lasserre on Twitter @christalestelas.

Related Articles

Stay on top of the most recent Horse Health news with

FREE weekly newsletters from

Sponsored Content

Weekly Poll

sponsored by:

What signs does your horse show when he has gastric ulcers? Please check all that apply.
74 votes · 189 answers

Readers’ Most Popular

Sign In

Don’t have an account? Register for a FREE account here.

Need to update your account?

You need to be logged in to fill out this form