Diarrhea in Young Foals

Infectious diarrhea in young foals can be fatal without prompt treatment, and the age of the foal can make a difference in his vulnerability to certain pathogens and how deadly they might be. In foals less than a week old, the cause is often salmonella or a clostridium bacteria.

Sam Jones, DVM, PhD, Dipl. ACVIM, associate professor of equine medicine at North Carolina State University, says diarrhea might also appear in foals that are septic (have infection in their bloodstreams) from other bacteria. They can get a blood infection from navel ill or bacteria that go through the gut lining soon after birth, and the resulting systemic infection creates diarrhea along with all the other signs.

During the first 24 hours of life, the foal has a very open gut that can absorb large molecules (to allow for absorption of antibodies from colostrum). If the foal ingests bacteria, they can also be transferred across to the bloodstream, explains Jones.

"If a mare has a dirty udder or the environment is dirty, the foal picks up a lot of bacteria," he says. "It is very important that the foal get adequate amounts of colostrum because it gives local protection within the gut as well as in the bloodstream."

Ability to absorb antibodies through the gut wall wanes during the first 24 hours; the first hours are most crucial for getting an adequate amount. "It's a gradual decline; the foal needs to get colostrum within the first six hours," says Jones. "It's a much less efficient process after that. If it's after six hours, and the foal seems ill, we often give him plasma or some other immunoglobulin supplement to make sure he gets the needed antibodies."


Bill Tracy, manager of Oak Tree Ranch, a Thoroughbred breeding facility in Bandera, Texas, says he milks out a sample of each mare's colustrum and weighs it to make sure the foal is getting adequate antibodies. "After you've done this a few times, you can milk a mare and know just from the feel and color whether it's good or not," he says. "It should be thick and greasy and stick to your hands like glue."

He saves colostrum from a few mares by freezing it. If there's any doubt about the quality of a mare's colostrum, he gives her foal some of the stored supply.


Foals infected during the first week of life with salmonella tend to get it from the mare, says Jones. "Between 5% and 10% of adult horses have salmonella in the GI tract and may pass organisms in manure," he says. "With the stress of foaling, mares often start to shed more bacteria. They'll have salmonella organisms around the udder and tail.

"If we have a problem with salmonella in a foal, we culture the mare to see if she has salmonella," he explains. "That can be useful for her next foal. We also take precautions because other mares in the herd might be infected. We need to reduce the likelihood of their foals becoming ill. In some cases--especially in an outbreak situation--we try to reduce fecal contamination around the udder when the foal is born. We may remove the foal and give it colostrum by tube until it gets well started."


Two strains of Clostridia affect foals: C. perfringens and C. difficile. Infection with C. perfringens bacteria, which live as spores in the environment, can be very severe if it affects the foal in the first week of life. "All foals get clostridial organisms colonizing the gut, but some C. perfringens produce toxins that can cause gut damage, and others don't," says Jones. The gut damage allows the toxins (and even the bacteria) to get into the bloodstream.

C. difficile can cause diarrhea in foals of any age. According to Cristina Robinson, DVM, a resident in equine medicine at The Ohio State University, the "bad" strain can produce at least five different kinds of toxins. In humans, when antibiotics are given to children, microorganisms in the large intestine change and can allow rapid proliferation of C. difficile, which then release toxins that can get through the gut lining and spread to the rest of the body, producing toxemia. In foals, however, this bacteria might invade the gut even without previous use of antibiotics.

Healthy foals that get good colostrum can still get C. perfringens infections in the first week of life. "They get severe bloody diarrhea, have organisms in the bloodstream, become septic, and may go into shock," he says. "It's harder to prevent this type of infection since the organism is present in the environment. Often it turns into an outbreak situation if there's enough of the organism around and it's a strain that produces toxins."

Foals younger than seven days might die if they develop this type of infection. They can be bright, then suddenly become ill and die (becoming dull or showing signs of abdominal pain, then collapsing and going into shock), sometimes before showing signs of diarrhea. C. perfringens can produce several types of toxins, including beta-toxin that causes necrosis (tissue death) of the intestinal wall and hemorrhaging.

"Some people have tried to vaccinate mares so there will be antibodies in the colostrum, to keep bacteria from infecting the foal," says Jones. "One of the most effective treatments, however, is to start the foal immediately after birth (if you are having problems with this type of infection) on an oral antibiotic called metronidazole (commercial name Flagyl). This keeps clostridial organisms from proliferating to the point of enough numbers to get the foal infected. It's the same antibiotic given to treat foals with this type of infection, but in this case we use it as a preventive."

Salmonella and clostridia are the major bacterial problems in young foals in the first week of life. "Occasionally we get foals with strains of E. coli that cause diarrhea, but it's not as common in foals as it is in calves," says Jones.

Viral Diarrhea

"Rotavirus is a common cause of diarrhea in foals older than a week," says Jones. "They contract it from the environment, usually from infected foals that are shedding it. If a foal ingests the virus, it can cause severe diarrhea, but it's more a fluid-losing diarrhea than the bloody diarrhea you see with salmonella or clostridia. It's less likely to be severe enough for foals to die, especially if they are treated appropriately with fluids."

With good supportive therapy, a foal might not need antibiotics. "Antibiotics won't kill the virus, but sometimes we put a foal on antibiotics to prevent additional problems," explains Jones. "If there's damage to the gut wall, there's risk of absorbing bacteria into the bloodstream." If the foal has rotavirus in conjunction with a bacterial diarrhea, it becomes much more serious.

"Rotavirus can infect foals from one week up to several months old," continues Jones. "It creates a watery diarrhea, and they can be systemically ill, but not usually as ill as foals with salmonella or C. perfringens. Control of rotavirus involves isolating affected individuals (which should be done with any type of diarrhea, whether bacterial or viral) so they are less likely to spread it to other foals."

At Oak Tree Ranch, Tracy uses an equine rotavirus vaccine given to mares ahead of foaling to create antibodies in the colostrum. The mares receive three injections in late pregnancy to build peak immunity and strong antibodies in the colostrum. Since the ranch began this program of vaccinating mares six years ago, they haven't had any serious diarrhea in the foals. Tracy says it's more economical to buy the vaccine and spend the time and effort administering it than to have diarrhea rampaging through the foals. The value of one lost foal would more than pay for all the vaccines for several years.


In many cases, treating foals with severe diarrhea is difficult to do on the farm; they usually need intensive care at a clinic. Fluid therapy is important for a foal with diarrhea to replace fluid and electrolytes being lost. If the problem is discovered quickly enough, when a foal is still able to absorb fluid through the gut, oral fluids can be given. Otherwise, the foal will need IV fluids. Often a young foal will need plasma containing antibodies if he's sick because he probably didn't get enough colostrum.

"When we get a sick foal, we take it to our vet clinic or to Texas A&M where the staff is geared to take care of it," says Tracy. "We do some fluid therapy here on the farm, but our foals are so valuable we prefer to take them someplace where they'll get the best care and treatment, and our insurance company prefers that, also. Then we all know we've done everything we can to save them."

Veterinarians at the hospital can also run tests to find which antibiotic might work best. "On the farm, it's a shotgun approach; if you give a foal unnecessary antibiotics, you are screwing up his gut," says Tracy. "You wipe out the normal intestinal flora, and it may take him longer to recover, or he may not recover."

Giving fluids to foals can be difficult, says Jones. "You can use a nasogastric tube, but this requires a veterinarian to pass the tube," he says. "Another alternative is to put a catheter into the jugular vein and give IV fluids. We prefer to do this in a hospital, where we can make sure we keep the foal hydrated and control the sodium, calcium, and potassium. Foals need to be closely monitored regarding fluid/electrolyte/glucose status. If they lose a lot of sodium, they may show neurological problems, becoming depressed, having seizures, or behaving in strange ways.

"If a foal is bright, alert, and nursing, he tends to keep himself hydrated," says Jones. "Sometimes we need to supplement the foal, but he stays reasonably well-hydrated as long as he's nursing well. But if he starts to get depressed and loses the desire to nurse, he can get into trouble very fast. Over a course of a few hours, he can become very dehydrated--especially in hot weather." Constantly monitoring foals' health status is crucial.

Early clues of illness are important to notice. Tracy says he can walk through a group of foals and pick out the one with diarrhea just by the smell of its tail. He says once you've smelled the bad kind of diarrhea, you never forget it. He also checks for dehydration by pinching skin on the cheek, and rubs an ear to check temperature. The main thing is constantly looking at foals.

"If you drive by and see five mares and foals in a pasture and one foal is lying off by himself, you stop and go check him," says Tracy.

Early intervention is crucial. Don't wait for a foal to show diarrhea; his condition can deteriorate quickly compared with an adult horse. Check the color of his gums, see how much he's nursing, feel the heart rate to see if it's going up, and check his temperature, advises Robinson. If it's above 102ºF (fever) or below 99ºF (the foal might be going into shock), have a vet check the foal immediately.

"Most crucial treatment of a severely sick foal is IV fluids and making sure electrolytes and blood pH are normal," says Jones. "Often foals that die are ones in which we are not able to maintain their fluid balance. It's also important to treat a foal appropriately. C. perfringens or C. difficile can be treated with metronidazole or penicillin. Salmonella can be treated with chloramphenicol."

Pepto Bismol can be given with the oral fluids (via nasogastric tube). Its bismuth subsalicylate has some antimicrobial effects and helps neutralize toxins and soothe the gut--reducing inflammation and secretions from the gut lining. Banamine can be given in low doses to ease pain and inflammation and combat endotoxemia. If a foal is severely dehydrated, however, it is not wise to use Banamine or any other anti-inflammatory drug due to the risk of kidney damage, says Robinson. The foal's hydration status should be continually monitored. 


A number of products are available to prevent foal diarrhea, including a vaccine against rotavirus (for mares). An oral paste can be given to newborn foals to give immunity against Escherichia. coli, and a number of probiotic pastes can help establish (or restore) proper gut flora. The theory behind the latter is that colonizing the gut with "good" flora helps crowd out the bad bacteria.

The best prevention is cleanliness, good colostrum (making sure the foal gets adequate colostrum soon enough), and knowing whether or not you have problems on the farm and dealing with those. If a mare drips milk before foaling, she loses the important antibodies. Milk the mare and put the colostrum in the freezer to give to the foal with a bottle as soon as he's born. A foal can also be given plasma in the first 48 hours if his IgG (one type of antibody) level is not high enough.

Some people treat a mare for parasites right after foaling, especially for Strongyloides westeri (threadworms), to keep the foal from being infected soon after birth. This tiny worm can make a foal more susceptible to infection with other pathogens.

Strict cleanliness when handling foals is important. Use gloves or clean hands when touching a foal for any reason. Avoid touching the umbilical area, don't let the foal suck your fingers or clothes, and keep the stall very clean. In the first two weeks of life, foals should be kept from contact with too many other animals or people to avoid spreading germs. When mares and foals are on pasture, it also helps to segregate them by age, rather than have young foals with older ones that might be shedding pathogens.

If there's a sick horse on the farm, isolate it so there is no chance for it to spread pathogens to healthy animals.--Heather Smith Thomas


About seven years ago, Fort Dodge Animal Health came out with a rotavirus vaccine, given to mares during late gestation. "It's a limited market," says Rocky Bigbie, DVM, MS, director of field veterinary services for Fort Dodge Animal Health. "The only folks that buy it are breeders who not only have had diarrhea in young foals on their farm, but have also nailed down the diagnosis and know it's rotavirus. Those who use it are staunch advocates because their foals seem to benefit.

"It's hard to show efficacy of a vaccine without a challenge model, but people who use it report a dramatic reduction in diarrhea problems," he says. "If you are using it to prevent something as obvious as diarrhea, you are going to know if it works or doesn't.

"At the University of Kentucky, Dr. Roberta Dwyer (DVM, MS, Dipl. ACVPM) was involved in trials for the vaccine," continues Bigbie. "It's a killed vaccine (1 cc dose, given intramuscularly) given to the pregnant mare at eight, nine, and 10 months of gestation to bolster maternal antibodies to peak level for the colostrum."

It is important to vaccinate the mares rather than the foals because this disease occurs in newborns. If you waited to vaccinate the foals, they would all have the disease before they could develop immunity from the vaccine. They might be exposed on day one, but if they obtain colostrum immediately after birth, they already have the protective antibodies they need (immunity from colostral antibodies is protective sooner that the foal's immune response to a vaccine).

"In most instances, mortality rate from rotavirus diarrhea is low, but many foals on the farm will be affected," says Bigbie. "It's debilitating to a foal. Treating the foal involves intensive care, and significant expense and labor. Foals get weak and dehydrated, and you have to help them up to nurse, hand milk the mare, or give the foal fluids." The cost and risk to the young foal's life make it much more attractive to give the vaccine to the mares to prevent the problem.--Heather Smith Thomas

About the Author

Heather Smith Thomas

Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey's Guide to Raising Horses and Storey's Guide to Training Horses. Besides having her own blog, www.heathersmiththomas.blogspot.com, she writes a biweekly blog at http://insidestorey.blogspot.com that comes out on Tuesdays.

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