Other Names
- Foal Heat Scours
- Neonatal diarrhoea (non-infectious)
What is Foal Heat Diarrhoea?
Foal heat diarrhoea — also known as foal heat scours — is the most common cause of diarrhoea in healthy foals in their first two to three weeks of life. It is a generally self-limiting, benign condition that typically occurs between 5 and 14 days after birth, coinciding roughly with the mare’s first oestrous (heat) cycle after foaling. Despite the timing correlation, research has not confirmed a direct causal link to the mare’s hormonal changes or to any alteration in milk composition.
The diarrhoea in foal heat scours is typically mild to moderate, semiformed to watery, and does not have the malodorous character of infectious diarrhoea. Affected foals usually remain bright, alert, and continue to nurse normally, which is the key feature distinguishing foal heat scours from more serious causes of neonatal diarrhoea that require urgent veterinary attention.
Understanding the difference between normal foal heat scours and pathological neonatal diarrhoea is essential for any owner or attendant responsible for newborn foals.
What Causes Foal Heat Diarrhoea?
Despite the name, the mare’s oestrus is not directly responsible. The exact mechanism remains incompletely understood, but several contributing factors are recognised:
- Gastrointestinal microbiome establishment: In the first week of life, the foal’s intestinal microbiome undergoes dramatic change as it transitions from the sterile in-utero environment to a complex microbial world. This transition, and the normal maturation of intestinal flora, is thought to be a primary driver of foal heat diarrhoea.
- Dietary transition: As foals begin to supplement milk with small amounts of pasture, hay, and creep feed, the introduction of solid material to the gut may alter intestinal transit and bacterial populations.
- Coprophagy: Young foals routinely eat the mare’s faeces (coprophagy), which is thought to help seed their own intestinal microbiome but may also temporarily alter gut function and transit time.
- Normal intestinal maturation: The neonatal equine gut undergoes rapid structural and functional maturation in the first weeks of life; the transient diarrhoea may simply reflect this normal developmental process.
Signs and Symptoms of Foal Heat Diarrhoea
The typical presentation allows experienced owners and vets to distinguish foal heat scours from more serious conditions:
- Age: Typically appears between day 5 and day 14 of life, peaking around day 7–10
- Character of diarrhoea: Semiformed to mildly watery; yellow or yellow-orange in colour; not foul-smelling
- Normal demeanour: The foal remains bright, active, and playful — this is the critical distinguishing feature. A foal with foal heat scours behaves like a normal foal.
- Normal nursing: The foal continues to nurse from the mare without reluctance
- No significant fever: Temperature within normal neonatal range (37.5–38.9°C)
- Perineal scalding: Skin around the hindquarters may become sore and irritated from prolonged contact with liquid faeces — this is the main welfare concern
- Duration: Typically self-limiting and resolves within 4–7 days without specific treatment
Diagnosis
Foal heat diarrhoea is a diagnosis of exclusion — it is made when diarrhoea in the appropriate age group occurs in a foal that is systemically well, and when infectious or other causes have been considered and are deemed unlikely. The diagnosis is largely clinical:
- Physical examination: A thorough examination including temperature, heart rate, hydration status, and assessment of demeanour is essential. Any sign of depression, dehydration, fever, or systemic illness should prompt immediate veterinary investigation for infectious causes.
- Faecal examination: In foals presenting with moderate or worsening diarrhoea, or when there is uncertainty, faecal ELISA or PCR testing for rotavirus, culture for Salmonella, and examination for parasites may be indicated.
- IgG level: If not already checked, confirm adequate passive transfer — foals with failure of passive transfer who also have diarrhoea need prompt escalated management.
Differential diagnoses that must be considered in any foal with diarrhoea include rotavirus, Salmonella, Clostridium difficile or perfringens enteritis, cryptosporidiosis, strongyloides infection, and — particularly in the first 24–48 hours — meconium impaction (constipation rather than true diarrhoea). See our equine rotavirus guide for more on infectious foal diarrhoea.
Treatment of Foal Heat Diarrhoea
Specific treatment is usually not necessary for mild, uncomplicated foal heat scours in a bright, well-hydrated foal. Management focuses on supportive care and monitoring:
- Monitoring: Check the foal’s temperature, heart rate, nursing behaviour, and hydration status twice daily. If the foal becomes depressed, stops nursing, develops a fever, or shows signs of dehydration, call your vet promptly.
- Perineal hygiene: This is the most important practical management step. Clean the hindquarters and inner thighs gently with warm water and mild soap to remove faecal contamination, then apply a barrier cream such as petroleum jelly (Vaseline) or zinc oxide cream to protect the skin from scalding. Repeat as needed. Leaving this unmanaged leads to painful scalding that can require veterinary treatment in its own right.
- Allow continued nursing: Do not restrict access to the mare. Milk is the foal’s primary nutritional and immune support, and continued nursing is important.
- Probiotics: Some owners use commercial equine probiotic products to support gut microbiome establishment during this period. While robust evidence is limited, they are generally safe and may be beneficial.
- Avoid unnecessary interventions: Foal heat scours does not require antibiotics, antidiarrhoeals, or oral electrolytes unless the foal becomes systemically ill. Over-treatment risks introducing complications.
Prevention of Foal Heat Diarrhoea
Because the underlying cause is likely normal physiological development, foal heat diarrhoea cannot be reliably prevented. However, certain measures support overall neonatal health and reduce the risk of complications:
- Ensure adequate colostrum intake: A foal with good passive transfer and a strong immune system is better equipped to handle any gastrointestinal challenge. Confirm IgG adequacy at 12–24 hours of age.
- Good foaling environment hygiene: A clean, dry foaling box with fresh bedding reduces the exposure of the neonatal foal to environmental pathogens during the period of intestinal microbiome establishment.
- Mare vaccination: Vaccination of the mare against rotavirus (where available) increases colostral antibody titres and may reduce the severity of any rotaviral component to early neonatal diarrhoea.
- Avoid introducing new horses near foaling time: New horses can bring unfamiliar microbial loads into the environment. Try to stabilise the yard’s horse population in the weeks before and after foaling.
Prognosis
The prognosis for straightforward foal heat diarrhoea is excellent. The vast majority of affected foals recover fully and without intervention within 4–7 days. Complications are uncommon in a foal that remains bright and is nursing normally. The main risk is secondary scalding if perineal hygiene is not attended to. Any foal that deteriorates, stops nursing, or develops a fever has exceeded the expected presentation of foal heat scours and requires immediate veterinary assessment — prognosis in these cases depends on the underlying cause.
When to Call the Vet
Call your vet if the foal with diarrhoea shows any of the following:
- Depression, dullness, or unwillingness to nurse
- Fever (temperature above 39.2°C or below 37.5°C)
- Rapid heart rate (above 80 bpm in a foal over 1 week old)
- Signs of dehydration (skin tenting, sunken eyes, dry gums)
- Profuse or blood-tinged diarrhoea
- Diarrhoea commencing in the first 4 days of life (before the typical foal heat window — this is more likely to be infectious)
- Diarrhoea persisting beyond 7–10 days
- Multiple foals in the yard affected simultaneously (suggests infectious cause)
When in doubt, call. Neonatal foals can deteriorate rapidly and early veterinary input costs far less than intensive treatment of a critically ill foal.
Frequently Asked Questions
Is foal heat diarrhoea dangerous?
In a bright, nursing foal, it is typically not dangerous and resolves without treatment. The danger lies in assuming it is “just foal heat scours” when in fact the foal has a more serious infectious diarrhoea. Always monitor closely and escalate to veterinary attention if the foal shows any signs of systemic illness. The bright, nursing foal with mild yellow scours at day 7–10 is reassuring; the dull, non-nursing foal with liquid diarrhoea at day 3 is a veterinary emergency.
How can I tell the difference between foal heat scours and infectious diarrhoea?
The key distinguishing factor is the foal’s systemic health. Foal heat scours: bright, playful, nursing well, mild-moderate yellow diarrhoea, no significant fever, typically day 5–14. Infectious diarrhoea: depression, lethargy, reduced or absent nursing, possible fever or hypothermia, more watery or bloody faeces, abnormal age (very young or outside the foal heat window), or multiple foals affected. If you are unsure, your vet can examine the foal and perform faecal testing to confirm.
Should I give my foal electrolytes for foal heat scours?
In most cases, no. A foal nursing normally is replacing fluid and electrolytes via the mare’s milk. Oral electrolyte supplementation is warranted only if the foal is showing signs of dehydration and is unable to maintain hydration through normal nursing. If the foal needs electrolytes, it likely needs veterinary assessment too — this level of dehydration in a neonatal foal is not a situation to manage alone.
Can the mare’s oestrus cause the foal’s diarrhoea through the milk?
This is the traditional explanation, but scientific evidence does not support it. Studies measuring the composition of mare’s milk during oestrus have not found significant differences that would explain the diarrhoea. The timing correlation is real but the mechanism is not direct hormonal transmission via milk. The current understanding favours intestinal microbiome maturation and dietary transition as the primary drivers, with the mare’s oestrus timing being coincidental rather than causal.