Intestinal disease is a fairly common problem in horses, young and old, skinny or fat, stall kept or pasture kept. As owners and veterinarians, most commonly we deal with not enough piles in the stall or the other extreme, watery diarrhea. From colicky, constipated horses to watery diarrhea and many stages in between, we must find ways to diagnose the related intestinal problems and successfully treat them. It is always our hope that this too shall pass.
The horse’s gastro-intestinal tract is a small biochemical company containing acids and bases, bacteria and protozoa, chemical or bacterial toxins, volatile chemicals, flammable gases, inert chemicals, dirt, sand, organic material and live and dead GI tract lining cells. The GI tract is composed of the oral cavity, the esophagus, the stomach, small intestines, large colon, small colon, caecum and rectum. The overall function of the GI tract is to get nutrients into the horse’s body, mix them with water, break them down into their component parts, facilitate the absorption of the components, and reabsorb most of the water found in the fecal material and discharge the remaining undigested organic and inorganic material. Any imbalance in the anatomy or the digestive physiology can result in disease. This can be an extensive list of specific diseases, but let’s focus on those that might cause diarrhea.
Many times when a horse’s stool changes from normal, formed, fecal balls to soft cow-pies, or worse, projectile watery diarrhea, we worry about an infectious cause from a bacterium like salmonella. Most horsemen have heard horror stories about horses acquiring salmonella infections with severe diarrhea and dehydration. But that bacterial infection is just one of the many causes of these clinical signs. The following is a discussion of some of the causes of diarrhea in foals and yearlings.
Foal heat diarrhea – almost every foal born will develop a soft to watery stool at the time the foal’s mother comes into heat about 9 days after the foal is born. It can start at 4-5 days of age and last about 14 days. Most foals are not at all clinically affected. They continue to nurse, chew on and eat small amounts of hay, drink water and play with their mother or other foals. The cause is unknown. It is self-limiting. Usually the foals stool is back to normal by 21 days of age. Diagnosis is based on clinical signs and history.
Foal Strongyloides diarrhea – This is a diarrhea disease of foals usually in the first month of life caused by an intestinal parasite called Strongyloides westerii. It is acquired through the milk from the mare and is easily preventable by deworming the mare about 4 weeks before she foals. The foals may be relatively normal but can get sick, dehydrated and die from complications of dehydration. Diagnosis is based on fecal exams
Ascariasis – This is commonly known as roundworms or ascarids. Ascarid is a general term referring to a large family of closely related parasites that infect a variety of vertebrates, including dogs, cats, horses, cattle, swine, birds, skunks, raccoons, and even humans. Most species of ascarids are host-specific, meaning they will grow to adults and reproduce in only a single type of host animal. So the ascarid of equids, Parascaris equorum, occurs in horses, donkeys, and zebras, but is not capable of infecting pigs or dogs. Foals are infected by ingesting the eggs from the pasture or stall. They hatch in the small intestine, migrate through the gut wall to the liver and the lungs (can cause significant coughing) and back to the gut. This takes about 10-12 weeks. So the foal can get sick anytime during this tissue migratory phase with signs relevant to the tissue that is being damaged. Foals or more often clinically ill than adults because as horses age they can actually develop and immunity (although not complete immunity) to the outer surface of the worms and mostly self-cure by about 15 months of age. . Clinically the foals and yearlings can look unthrifty, lose weight, and fail to thrive, cough, or develop diarrhea or obstructive disease resulting in colic. Diagnosis is based on observing the worms in the stool, clinical signs and fecal exams.
Cyathostomiasis – This is the family of intestinal parasites that includes Strongylus vulgaris commonly referred to as blood worms. The foals get infected by ingesting the infective L-4 larvae in the bedding or pasture, the larvae migrate into the small vessels (arterioles) in the caecum and large colon, re-emerging in the gut to mature and lay more eggs. Diarrhea will result when the larvae re-immerge into the gut. The diarrhea disease is
generally not severe. Diagnosis is based on clinical signs, physical exam and fecal exams.
Viral Diarrhea – Four different viruses have been isolated from foals with diarrhea. Rotavirus can affect 40% of a farm foal population. It attacks the lining of the small intestine resulting in the denuding of the small villi projections in the lining responsible for normal absorption. The resulting disease includes fevers and profuse watery diarrhea requiring aggressive medical therapy. It is preventable by vaccinating the mare during the last 3 months of the pregnancy, thereby conveying immunity to the foal through the colostrum. Adenovirus has been isolated but its role in diarrhea disease is still to be defined. Coronavirus is a fairly newly defined disease affecting foals and adult horses. It can affect 30% of the horses in a herd resulting in high fevers, colic, diarrhea and secondary large colon displacement. If uncomplicated it usually runs its course in 5-7 days with symptomatic treatment to control the fevers, the colic and the fluid loss. Parvovirus has been described as a cause for foal diarrhea. Though well defined in other species (dogs especially), little is known about the disease in foals. Diagnosis for all these viral diseases is based in clinical signs, fecal exams, fecal cultures, blood work, and PCR DNA testing.
Bacterial diarrhea – Generally these are one of 3 causes. First, is the most often discussed, caused by Salmonella sp. This disease presents with fever, depression, colic, sudden onset severe watery diarrhea, with severe dehydration. Second are Clostridium perfringens and C. difficile. These also cause fever, depression, colic, sudden onset severe watery diarrhea, with severe dehydration. Some foals have blood-tinged diarrhea which seems to carry a far worse prognosis. The last bacterial diarrhea in this discussion is called proliferative enteropathy and it is caused by Lawsonia intracellulare. This is usually in weanling foals. Signs also include fever, depression, colic, sudden onset severe watery diarrhea, with severe dehydration. Because all these bacterial diseases present with similar clinical signs, specific laboratory diagnostic tests are necessary to accurately diagnose the specific disease. Salmonella spp. and Clostridium spp. can cause disease in humans (zoonotic). Great care should be taken to avoid human cases.
Protozoal diarrhea – Cryptosporidium ssp., Eimeria leukarti, Trichomonas equi, and Giardia equi have all been isolated from foals with diarrhea. But, these organisms have been isolated from foals with normal stool as well, so just how involved these organisms are in the development of diarrhea disease is a bit uncertain. These organisms have zoonotic implications so extra care should be taken in treatment and management of these pathogens.
These are the most common causes of foal and yearling diarrhea. This coming spring and summer, if you have foals or yearlings that develop changes in the consistency of their stool (anything from slightly soft to projectile watery diarrhea) contact your veterinarian at Brenford Animal Hospital immediately. Thorough examines and diagnostic laboratory tests are necessary. Waiting too long can result in non-treatable organ failure. Early diagnosis and treatment provides the best opportunity for complete recovery. - PFH (2.11.14)
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