In foals, causes of diarrhea include foal-heat diarrhea, antibiotics, overeating, parasites, lactase deficiency, viruses,
ulcers and bacteria.
Foal heat diarrhea is the most common cause of diarrhea in foals seven to 14 days of age. The cause is unknown but is probably the result of changes in intestinal cell populations or establishment of normal gut microflora. Foals will often continue to nurse and remain bright and alert, without fever. If the diarrhea persists for more than a few days and the foal becomes depressed with a fever, a thorough work-up by your veterinarian is indicated.
Several different viruses and bacteria may cause severe diarrhea in foals, including rotavirus and salmonella. The foal will become depressed and febrile, will stop suckling, and may show signs of colic with profuse watery to bloody diarrhea. All of these signs should alert the owner, and rapid intervention by your veterinarian is essential. If therapy is not initiated quickly, the foal will die.
Complications in foals
and adult horses are very different
There are several parasites--most commonly strongyloides--that will cause diarrhea in foals. These parasites pass through the mare's milk into the foal. Foals may also infect themselves by eating feces. A good preventive medical program, including deworming the mare in her last trimester of pregnancy, will help.
Lactose intolerance in foals, as in human infants, has been described as a cause of diarrhea. These foals may appear to recover but then will suffer a prolonged course of diarrhea. Recommendations from your veterinarian will include withholding the mare's milk, replacing it with special dietary supplements.
Gastric ulcers, especially in foals several weeks to months of age, have been incriminated as a cause of chronic diarrhea. In addition to the diarrhea, affected foals may appear unthrifty and show colic-like signs, such as grinding teeth and rolling onto their backs for extended periods. Once properly diagnosed by your veterinarian, ulcers can be treated medically, and the diarrhea should subside.
Several management factors have been identified to minimize the risk of diarrhea in foals. These include disinfecting foaling stalls between uses; using wood shavings rather than straw or sawdust for bedding; washing the mare's udder before the foal nurses; and eliminating the use of prophylactic antibiotics in foals.
If the foal becomes depressed and febrile and stops nursing, with signs of colic and profuse, watery or bloody diarrhea, call your veterinarian immediately.
In adult horses, several inflammatory conditions of the large intestine can lead to diarrhea. Often, the performance of the horses will suffer due to losses of valuable electrolytes, protein and fluid in the feces.
With careful management practices, many causes of diarrhea in adult horses will resolve themselves. However, some cases, especially those caused by infectious agents, may require your veterinarian. The causes of diarrhea in adult horses can include poor dental care, sand-induced diarrhea, nervousness, bacteria (salmonella, Potomac Horse Fever- PHF), internal parasites, cancer/neoplasia and antibiotics.
Bad teeth, especially in older horses, may cause diarrhea. If feed is not properly ground, it will lead to irritation and inflammation of the intestine and ultimately cause diarrhea. Regular dental care along with good hay and grain often eliminates this situation.
Many owners have observed their horses experiencing temporary diarrhea at a show or event or after a particularly exhausting trail ride. These horses generally benefit from electrolyte supplements and free access to fresh water. Most of these horses return to normal, and the diarrhea subsides after they have returned to their home environment and the stress has been eliminated.
Several different internal parasites (for instance, strongyles) cause inflammation of the large intestine which may result in diarrhea. Heavily parasitized horses will often have an unthrifty appearance and lack energy. A good rotational deworming program solves this problem.
Other causes of diarrhea, and in particular those caused by infectious agents such as salmonella and Potomac Horse Fever, require evaluation by your veterinarian. In addition to profuse, watery diarrhea, clinical signs may include fever (greater than 102.5 F); fetid odor of feces; blood in feces; elevated heart and respiratory rates; purple mucous membranes; colic-type signs; dehydration; cool/cold extremities and severe depression.
With prompt intervention by both the owner and veterinarian, many of these horses can be treated and saved. However, some horses may require intensive care at a referral center or hospital. If, for example, Potomac Horse Fever is diagnosed, a vaccine is available that may protect the horse against future PHF infections. Unfortunately, no vaccine is available against salmonella.
Another common frustration to horse owners is the chronic "cow-flop" type of diarrhea. This type of diarrhea may be caused by either chronic ingestion of sand or a disruption in the balance of the normal microflora that inhabit the gut.
Other more serious causes of chronic diarrhea include chronic salmonella infection and cancer. Regardless of the cause, chronic "cow-flop" diarrhea should be investigated by your veterinarian. If it is caused by salmonella, this could pose a threat to other horses on the farm and potentially lead to the life-threatening acute form of diarrhea. Sand-induced diarrhea may be dealt with either medically or surgically.
If the chronic diarrhea is caused by cancer of the intestinal tract, the prognosis for survival is poor.