Diarrhoea in dogs
AHDS (previously called haemorrhagic gastroenteritis or HGE)
Why AHDS is an emergency
AHDS can cause very rapid fluid loss and dehydration. Some dogs may develop poor circulation and shock, even when the amount of diarrhoea seen at home does not appear large. Veterinary assessment is important.
What is AHDS?
AHDS is a sudden and potentially serious intestinal illness in dogs. It typically causes profuse, watery diarrhoea containing fresh blood. Vomiting, nausea, abdominal discomfort, tiredness and reduced appetite are also common. Any breed can be affected, although small and middle-aged dogs are frequently represented.
The exact cause of AHDS is not fully understood. In most dogs, no specific infectious cause is identified, and AHDS is not generally considered contagious. Dietary indiscretion, such as eating rich, unfamiliar or spoiled food, scavenging, or a sudden diet change, is commonly reported before an episode and may contribute to its development. Good hygiene around vomit and faeces is always recommended.
What signs might I see?
• Sudden onset of frequent, watery or “jelly-like” bloody diarrhoea
• Vomiting, which may occasionally contain blood
• Reduced appetite, nausea or drooling
• Abdominal discomfort, restlessness or a hunched posture
• Weakness, lethargy, pale gums or collapse in severe cases
Seek urgent veterinary care. Contact a veterinarian promptly if your dog has repeated bloody diarrhoea, cannot keep water down, appears weak or painful, has pale gums, collapses, or if you are concerned.
How is AHDS diagnosed?
There is no single test that confirms AHDS and it is oftentimes a diagnosis by exclusion (meaning other possible causes must be ruled out before AHDS is considered the most likely diagnosis). Your veterinarian makes the diagnosis from your dog’s history, examination findings and test results, while ruling out other important causes of bloody diarrhoea. These may include parvovirus, intestinal parasites or infection, pancreatitis, toxin exposure, a gastrointestinal foreign body, clotting disorders, Addison’s disease and other intestinal or systemic illnesses.
Recommended tests depend on your dog’s age, vaccination status, examination and illness severity. They may include:
• Packed cell volume (PCV) and total solids: assess red blood cell concentration, hydration and blood protein. Dogs with AHDS commonly have concentrated red blood cells with normal or reduced protein.
• Complete blood count and biochemistry: assess inflammation, anaemia, electrolytes, blood glucose, protein levels and organ function.
• Faecal or infectious disease testing: may be recommended, particularly for young, unvaccinated or high-risk dogs.
• Abdominal imaging: radiographs or ultrasound may be used when a foreign body, obstruction, pancreatitis or another abdominal problem is possible.
• Additional testing: such as clotting tests, urinalysis or an ACTH stimulation test, may be advised based on the individual patient.
Important: Do not give human anti-diarrhoeal, pain-relief or anti-inflammatory medication unless specifically instructed by a veterinarian. Some products can be dangerous for dogs or may mask worsening disease.
How is AHDS treated?
Treatment is tailored to the severity of illness. Dogs with significant dehydration, ongoing fluid losses or poor circulation usually require hospitalisation and intravenous fluid therapy. Close monitoring is important because fluid and protein losses can change quickly.
• Intravenous fluids: replace losses, restore circulation and correct dehydration and electrolyte changes.
• Anti-nausea medication: helps control vomiting and allows feeding to restart.
• Pain relief: is provided when abdominal discomfort is present.
• Early nutrition: small amounts of an appropriate, easily digested diet are offered once vomiting is controlled. A feeding tube may be considered if a patient cannot eat for a prolonged period.
• Probiotics or other gut-support products: may be recommended in selected dogs. Benefits vary between products, and they do not replace fluid therapy or monitoring.
• Antibiotics: are not routinely needed for stable dogs with AHDS and do not usually speed recovery. They are reserved for patients with suspected sepsis, marked immune compromise, severe neutropenia (a very low number of infection-fighting white blood cells) or another confirmed bacterial infection.
What is the outlook?
With timely supportive care, the prognosis is generally very good. Many dogs improve substantially within 24-48 hours, although hospitalisation for several days may be required in more severe cases. Stools can remain soft or contain small amounts of blood while the intestine heals and may take several days to return fully to normal.
A small number of dogs can deteriorate despite treatment, particularly if they develop shock, severe protein loss, sepsis or another underlying condition. Your veterinary team will discuss your dog’s response and expected recovery with you.
Clinically reviewed and approved by Dr Giulia Agostini, Pet Emergency Senior Veterinarian and Clinical Manager, DVM MANZCVS (ECC) August 2026