Diarrhea in Foals: General Overview

Diarrhea in Foals: General Overview

By Siobhan McAuliffe, MVB, DACVIM, Foal Medicine Specialist

Part 1 in a 3-part series on diarrhea in foals

Diarrhea is the most common ailment of foals, with almost every foal experiencing diarrhea at some point. As an owner, it can be challenging to determine if the diarrhea your foal is experiencing could be life threatening, when you should seek veterinary advice and what treatment, if any, should be given.

Differential diagnosis of diarrhea in foals by age group

0-10 days

Non-infectious diarrhea

  • Foal heat diarrhea
  • Diarrhea secondary to meconium impaction
  • Errors of feeding: incorrect volume or frequency, especially in orphaned foals
  • Congenital lactose intolerance (infrequent)
  • Gastric ulceration (infrequent)
  • Sand enteritis/colitis (infrequent)
Infectious diarrhea

  • Viral infections: Rotavirus, Coronavirus, Adenovirus
  • Bacterial infection:
    • Gram-positive enterocolitis: Clostridium spp.
    • Gram-negative enterocolitis: Escherichia coli, Salmonella spp., Actinobacillus spp.
  • Fungal infection: Candida spp., Mucor spp.
  • Protozoal infection: Cryptosporidium spp.

10 days to 6 weeks

Non-infectious diarrhea

  • Foal heat diarrhea (normally seen up 2 weeks of age)
  • Dietary induced diarrhea:
    • errors of feeding
    • post enteritis lactose intolerance
    • dietary hypersensitivity (infrequent)
    • copper deficiency (infrequent)
    • sand enteritis/colitis (infrequent)
  • Antibiotic-associated diarrhea
  • Gastric ulceration
Infectious diarrhea

  • Viral infections: Rotavirus, Coronavirus
  • Bacterial infection:
    • Gram-positive enterocolitis: Rhodococcus equi (uncommon in foals less than 6 weeks), Clostridium spp.
    • Gram-negative enterocolitis: Escherichia coli, Salmonella spp., Actinobacillus spp., Campylobacter spp.
  • Fungal infection: Candida spp., Mucor spp.
  • Protozoal infection: Cryptosporidium spp.
  • Parasitic infection: Strongyloides westerii, Parascaris equorum, Strongylus vulgaris 

6 weeks to 6 months

Non-infectious diarrhea

  • Dietary induced diarrhea:
    • errors of feeding
    • post enteritis lactose intolerance
    • dietary hypersensitivity (infrequent)
    • copper deficiency (infrequent)
    • sand enteritis/colitis (infrequent)
  • Antibiotic-associated diarrhea
  • Gastric ulceration
Infectious diarrhea

  • Viral infections: Rotavirus, Coronavirus
  • Bacterial infection:
    • Gram-positive enterocolitis: Rhodococcus equi, Clostridium spp., Lawsonia intracellularis
    • Gram-negative enterocolitis: Escherichia coli, Salmonella spp., Actinobacillus spp., Campylobacter spp.
  • Fungal infection: Candida spp., Mucor spp.
  • Protozoal infection: Cryptosporidium spp.
  • Parasitic infection: Strongyloides westerii, Parascaris equorum, Strongylus vulgaris

Non–infectious causes of diarrhea include: Foal heat diarrhea, errors in feeding, antibiotic-induced diarrhea and secondary to gastric ulcers or meconium impaction.The most common of these is foal heat diarrhea (scours). This is the diarrhea that occurs in foals between seven and 10 days of age. It is called foal heat diarrhea because the foal’s dam usually is experiencing her first heat or estrous cycle (called the foal heat) after foaling around this time.

It was previously thought that the heat cycle in the mare resulted in the foal having diarrhea due to hormonal changes in the mare’s milk composition. However, orphaned foals or foals raised separated from the mare also develop diarrhea during this time.  What veterinarians believe is happening at this point is that the population of normal bacteria (flora) is becoming established in the foal’s intestine and this causes a transient change in digestive processes which results in diarrhea. Foals are often seen eating feces (coprophagia) just before the onset or during the period of the foal heat diarrhea. Although this behavior is not appealing to watch, it is indeed normal as this is the way young foals populate their GI tract with the ‘good’ bacteria that they will need to help them digest and utilize their future grass diet.

The main distinguishing factor between foal heat diarrhea and other infectious causes of diarrhea—such as rotavirus or a bacterial infection—is the lack of systemic illness.  Therefore, foals experiencing foal heat diarrhea do not have a fever, they remain bright and alert, and they continue to nurse well and remain active. Foal heat diarrhea is usually mild and self-limiting and rarely does the diarrhea become watery in consistency.

Other non-infectious causes of diarrhea such as feeding errors will often have a history to implicate them as a possible cause. This for example is frequently seen in orphaned foals, which are bucket fed. Errors can occur in the concentration of the milk replacer used or the frequency of feeding.

Lactase is made by the cells in the tips of the small intestinal mucosal brush border. Primary lactase deficiency is rare in foals, but lactase deficiency secondary to damaged intestinal villi tip cells by infectious agents such as rotavirus and Clostridium difficile is not uncommon. Supplementation with a lactase is indicated in foals with suspected lactase deficiency. Although lactose intolerance can be confirmed with a lactose tolerance test, as supplementation is inexpensive, practical and safe, testing is not usually performed. Similar to foal heat diarrhea, these foals will not be systemically ill and they remain bright, active and fever free.

It is important to remember that foals of this age can also be affected with other, more serious forms of diarrhea. Foals with infectious causes of diarrhea have a ‘whole body’ or systemic response to the infection and will usually be depressed and quiet. In addition to this change in attitude there are several other ways to tell the difference:

  1. Determine if your foal has a fever. A foal’s normal rectal temperature is between 99° and 101.5º F.
  2. Monitor your foal to make sure he/she is nursing adequately. A normal healthy foal will nurse several times an hour and will run to nurse the mare on someone entering the stall. If the mare’s udder is very full and possibly dripping milk, or if the foal has ‘milk staining’ of the forehead, then most likely the foal is not nursing adequately and is sick. Foals with foal heat diarrhea have a mild, self-limiting diarrhea, whereas foals with infectious causes often have profuse, watery diarrhea.
  3. Monitor your foal for diarrhea. Foals, which are nursing, will produce a yellowish, pasty manure (milk feces), which is totally normal. Foals with diarrhea will have more watery feces that can be variable in color, and diarrhea often stains their hindquarters or can be seen dripping from the tail.

If you note any of the above signs in your foal you should contact your veterinarian immediately and isolate the mare and foal from other young stock until the likely cause of the diarrhea can be determined.

Continue to Part 2: Infectious Diarrhea


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