CONDITION
Acute Haemorrhagic Diarrhoea Syndrome (AHDS)
Acute haemorrhagic diarrhoea syndrome is a condition in which a dog develops sudden, profuse, bloody diarrhoea—often described as resembling raspberry jam—alongside vomiting and signs of feeling unwell. The cause remains uncertain, though it appears to involve inflammation and increased permeability of the intestinal lining, allowing fluid to shift rapidly out of the bloodstream and into the gut. It tends to occur without warning in otherwise healthy dogs, and the volume of fluid loss can be striking. Owners typically notice the sudden onset of severe, bloody diarrhoea, often with a characteristic bright red or dark red appearance, and the dog may seem quieter, less interested in food, or visibly uncomfortable. The condition can look alarming because of the volume and colour of the diarrhoea, and many owners arrive at this page trying to understand what they are observing and what may be happening inside. This page explores the signs that accompany acute haemorrhagic diarrhoea syndrome, the mechanisms thought to underlie it, how it is distinguished from other causes of bloody diarrhoea, and the approaches used to support affected dogs through recovery.
Why this matters now
Acute haemorrhagic diarrhoea syndrome can occur at any age. Some case series report a median age of around five years, while a UK study of dogs under primary veterinary care found the presentation more likely at the extremes of age, under three years and over nine years, than in dogs in between. Small and toy breeds—including Yorkshire terriers, miniature schnauzers, miniature poodles, and Maltese—appear to be disproportionately represented, though the condition can develop in any dog. It typically arises without an obvious preceding trigger, appearing suddenly in an otherwise healthy animal. In puppies and in dogs that are unvaccinated or have not completed their vaccinations, the same combination of vomiting and bloody diarrhoea is more often associated with parvovirus infection, which is contagious to other dogs and can be fatal.
The condition often begins with vomiting, which may precede the appearance of bloody diarrhoea by several hours. The diarrhoea itself can be profuse and striking in appearance, and the volume of fluid loss may seem disproportionate to what the owner has observed being passed. Fluid loss can become severe within hours, and the condition can be fatal without treatment, though reported deaths run under one in ten dogs that receive hospital-based fluid support. Because the fluid is lost mainly from the bloodstream, the familiar outward signs of dehydration can lag behind what is happening in the circulation, and the extent of the loss cannot be reliably judged at home. Many dogs show rapid improvement within the first day of supportive care, and the majority recover fully over a period of two to three days, though individual variation in the pace and completeness of recovery does occur.
Signals & patterns
Early signals
Vomiting before diarrhoea starts
Many dogs begin vomiting several hours before the bloody diarrhoea appears. The vomiting may be intermittent and the dog may seem quieter or less interested in food during this time.
Sudden onset of bloody diarrhoea
The diarrhoea often appears abruptly, with a characteristic bright red or dark red colour and liquid consistency, sometimes likened to raspberry jam. The volume passed can be larger than expected, and the dog may strain or seem uncomfortable.
Reduced appetite or reluctance to eat
The dog may turn away from food or show less interest in meals. This often accompanies the vomiting and can begin before the diarrhoea becomes obvious.
Quieter demeanour or lethargy
Owners may notice the dog is less active, resting more than usual, or not engaging in normal play or interaction. This shift in behaviour can be subtle at first.
Later signals
Signs of dehydration
As fluid continues to shift out of the bloodstream, the dog may develop a dry mouth, sunken eyes, or skin that is slower to spring back when gently lifted. The degree of dehydration can seem greater than the visible fluid loss would suggest.
Weakness or reluctance to stand
Some dogs become visibly weaker as the condition progresses, moving less readily or appearing unsteady. This reflects the ongoing loss of circulating fluid and the body's struggle to maintain normal function.
Pale or tacky gums
The mucous membranes inside the mouth may appear paler than usual or feel dry and sticky to the touch, both of which can accompany significant fluid loss and reduced circulation.
Click to read about the biological mechanisms
How this is usually investigated
The investigation typically begins with a detailed account of when the signs started, what the diarrhoea looks like, and whether the dog has eaten anything unusual or has been unwell in other ways. Physical examination may reveal signs of dehydration, abdominal discomfort, or changes in heart rate and mucous membrane colour. Laboratory tests can help confirm the characteristic pattern of haemoconcentration, rule out other causes of bloody diarrhoea, and guide decisions about fluid support. Canine parvovirus infection produces a very similar picture of vomiting and bloody diarrhoea, and the two cannot be told apart at home or by the appearance of the diarrhoea. A faecal parvovirus test is a standard part of the work-up for this presentation, and it carries particular weight in puppies and in dogs that are unvaccinated or have not completed their vaccinations.
Complete blood count
Chemistry panel
Faecal analysis
Abdominal ultrasound
Parvovirus antigen test
Options & trade-offs
Management centres on restoring and maintaining circulating fluid volume, supporting the body while the intestinal lining repairs itself, and monitoring for complications. Different dogs respond at different rates, and the approach may be adjusted depending on how quickly signs improve, the severity of fluid loss, and practical considerations around the setting of care. What works well for one household or one animal may not suit another, and the intensity of support can be tailored to the individual case.
Intravenous fluid therapy
Fluids are administered directly into a vein to rapidly replace the volume lost through diarrhoea and vomiting, correct electrolyte imbalances, and support blood pressure and organ perfusion. The rate and composition of fluids can be adjusted based on ongoing losses and laboratory findings. This approach typically requires hospitalisation with continuous monitoring.
Trade-offs: Intravenous fluids can address severe dehydration quickly, but they require placement of a catheter, carry a small risk of infection or phlebitis, and involve the practical considerations of keeping the dog hospitalised. Some dogs find the hospital environment stressful, though the clinical benefit often outweighs this concern.
Restricted feeding and gradual reintroduction of food
Food is withheld for a period—often 12 to 24 hours—to allow the inflamed intestinal lining to settle, then reintroduced gradually in small, easily digested portions. The choice of food and the pace of reintroduction can be adjusted depending on how the dog tolerates each step. Some dogs resume normal eating within a day or two, while others require a more cautious approach.
Trade-offs: Resting the gut can reduce stimulation of an inflamed intestine, but prolonged fasting may delay healing in some animals, and individual tolerance varies. Dogs with concurrent conditions or very small body size may need closer attention to energy balance.
Antimicrobial therapy
Antibiotics may be considered if there is concern about bacterial translocation across the damaged intestinal barrier or if the dog shows signs of systemic infection. The choice of agent and duration can vary depending on clinical judgement and the severity of signs. Not all dogs receive antibiotics, and some recover fully without them.
Trade-offs: Antimicrobials may reduce the risk of bacterial complications in dogs with severe mucosal damage, but they carry the usual considerations around side effects, disruption of normal gut flora, and contribution to antimicrobial resistance. Their use is more common in dogs showing marked systemic signs or those that do not improve rapidly with fluid support alone.
Anti-nausea and gastric protection medication
Drugs that reduce vomiting and protect the stomach lining can improve comfort and may help the dog tolerate oral fluids or food more readily. These medications are often given by injection initially, then transitioned to oral forms as the dog's condition stabilises.
Trade-offs: Controlling nausea can make the recovery period less distressing and may reduce the risk of oesophageal irritation from repeated vomiting, but these medications do not address the underlying intestinal damage. They are typically used as part of a broader supportive approach rather than in isolation.
Common misconceptions
"Acute haemorrhagic diarrhoea syndrome is caused by a specific dietary indiscretion or toxin that can be identified and avoided in future."
The condition often arises without an identifiable trigger. While dietary change or stress may occasionally precede the onset, the underlying cause remains uncertain, and there is no single food or substance reliably associated with the syndrome. Many dogs experience a single episode and do not have recurrences, even without changes to diet or environment.
"The bright red colour of the diarrhoea means the bleeding is coming from the stomach or upper intestine."
In acute haemorrhagic diarrhoea syndrome, the blood typically originates from the small or large intestine, where increased permeability allows red blood cells to leak into the gut lumen, rather than from the stomach. Colour is an imperfect guide to where bleeding is coming from: how red or dark it appears is affected by transit time and mixing with intestinal contents, and blood from higher up the gut can also look darker because it has been partly digested on the way down. Because these effects overlap, colour alone cannot reliably localise the source of bleeding.
"Once a dog has had acute haemorrhagic diarrhoea syndrome, it is likely to recur or indicates an underlying chronic bowel problem."
Most dogs experience a single episode and recover fully without ongoing gastrointestinal issues. Recurrence is uncommon, and the majority of affected animals do not go on to develop chronic enteropathy or other long-term intestinal conditions. The prognosis following recovery is generally favourable, though a small proportion of dogs may have repeated episodes, and in those cases further investigation may be considered.
Related conditions
Canine Parvovirus
Canine parvovirus is an important differential diagnosis when a dog presents with sudden bloody diarrhoea, though dogs with parvovirus tend to be young and unvaccinated, and typically show low blood cell counts rather than the marked haemoconcentration seen in acute haemorrhagic diarrhoea syndrome.
Colitis
Colitis describes inflammation of the large intestine and can produce bloody diarrhoea with mucus, though the pattern often involves frequent small-volume stools with straining, which differs from the sudden, profuse, raspberry-jam appearance characteristic of acute haemorrhagic diarrhoea syndrome.
Acute Pancreatitis
Acute pancreatitis can occasionally present alongside bloody diarrhoea, with some studies noting a possible association between the two conditions, though diarrhoea with blood appears in around a third of pancreatitis cases and may differ in volume and character from the profuse haemorrhagic presentation typical of acute haemorrhagic diarrhoea syndrome.
Campylobacteriosis
Campylobacteriosis is a bacterial infection of the digestive tract that can produce diarrhoea containing mucus or blood, and enters the differential diagnosis for dogs presenting with sudden gastrointestinal signs, though the history, age, and degree of haemoconcentration may help distinguish it from acute haemorrhagic diarrhoea syndrome.
Once treatment has been given and signs have settled, it can be helpful to observe how the dog responds to the gradual return to normal diet and activity, and to note any patterns that might emerge over time. For dogs that have recurrent episodes, keeping a simple record of when each episode occurred, what the dog had eaten or been exposed to beforehand, and how quickly it resolved can help build a picture over time and is useful information to bring to a future conversation.
Last reviewed: 13 September 2026 · Dr Alastair Greenway MRCVS