Onion and garlic poisoning in dogs

Overview

Onion, garlic and other alliums

Onion and garlic belong to the same plant genus as leeks and chives. Onion and garlic are its most common poisoning causes. Raw and cooked onion can both damage canine red cells. Garlic is estimated to be three to five times more toxic than onion.

Haemolytic anaemia means red cell numbers fall through destruction. Too few red cells impair oxygen transport.

Onion and garlic powder can cause greater exposure than the food's appearance suggests because dried ingredients are concentrated.

The UK's veterinary poisons advice service recorded 69 canine allium poisoning cases during 1994–2008. Two dogs died and two were euthanased.

Heating or drying does not remove alliums' harmful effects on red cells.

Causes

How red cells are damaged

Allium sulphur compounds are considered the main cause of red cell destruction. Chopping or chewing releases damaging compounds. Digestive microbes also release them from onion. Once absorbed, they cause oxidative injury to red cells.

Some haemoglobin becomes methaemoglobin, which cannot transport oxygen normally. Red cell changes and raised methaemoglobin can be detected within 24 hours of exposure. These changes peak at around 72 hours. Red cell destruction usually occurs three to five days after exposure.

Heinz bodies form when oxidised haemoglobin precipitates within red cells. Oxidative damage can also alter cell shape, concentrating haemoglobin on one side. Direct oxidation of the cell membrane also promotes destruction.

Effects of different garlic forms

A laboratory experiment exposed canine red cells to extracts of fresh, dried and granulated garlic. Granulated garlic extract produced Heinz bodies in an average of 15.0% of cells. Fresh garlic extract produced them in an average of 5.0%.

Red cell levels after exposure

In an experiment feeding dogs onion on three days, haematocrit on day five was 40% of its pre-exposure value. It returned to normal within 10–14 days after exposure ended. Numerous Heinz bodies were seen on day two. High numbers persisted for four days.

Risk factors

Concentrated products such as dried onion flakes and powder are common exposure sources. Dry onion soup mix also contains concentrated onion. A large single ingestion can cause poisoning, for example from onion-containing scraps. Repeated exposure can also reduce red cell numbers even with small amounts each time.

Risk assessment needs the dog's weight and estimated onion consumption.

Some dogs are genetically more susceptible because of unusual red cell composition. This characteristic occurs in some Akitas and Shiba Inus, for example. Homemade garlic preparations can also expose dogs if given as intended for people.

The same onion quantity causes greater exposure relative to size in small dogs. Allium poisoning has also occurred after a dog ate steamed dumplings containing Chinese chives and garlic.

Typical symptoms

Visible anaemia signs often start only after substantial red cell destruction.

• Weakness or lying down more readily than usual.
• Tiring more quickly on normal walks.
• Faster breathing even at rest.
• A faster heartbeat.
• Loss of appetite.
• Yellowish gums or whites of the eyes.
• Reddish or brown urine from excreted haemoglobin.

Severe poisoning can cause collapse.

Preparations containing fresh garlic can irritate the stomach and intestinal lining. Vomiting or diarrhoea can precede anaemia signs.

Symptoms can start after just one day or later, depending on ingestion. Abdominal tenderness can occur while signs are mainly digestive. As anaemia progresses, mucous membranes may become pale and later yellowish.

Complications and consequences

Severe anaemia and kidney injury

Extensive red cell destruction can cause life-threatening anaemia. Released haemoglobin can damage kidneys as it passes into urine. Severe poisoning can be fatal.

Profuse vomiting and diarrhoea can cause dehydration before anaemia develops. Anaemia and methaemoglobin accumulation can simultaneously impair tissue oxygenation. Raw garlic cloves were found in the stomach in one fatal case. Small haemorrhages occurred at several sites in the heart muscle. Blood values could not be measured before this dog's death.

Diagnosis at the vet

Exposure history and blood tests

The vet combines food history with blood results and symptoms. A smear can reveal Heinz bodies in red cells. By the time extensive haemolysis is identified, methaemoglobin may no longer be raised.

A complete blood count establishes anaemia severity at examination. Reticulocytes are young red cells reflecting the marrow's response. This response usually appears in blood three to five days after anaemia begins. Haematocrit may be rechecked because its lowest value can occur several days after onion ingestion.

Findings in a dog that ate garlic

A published case described a six-year-old Schnauzer examined two days after eating baked garlic. Haematocrit, the proportion of blood occupied by red cells, was 22%. Methaemoglobin was 8.7%. Alongside Heinz bodies, the smear showed red cells with haemoglobin concentrated at one edge.

Urinalysis and other anaemia causes

Urine and blood results together help assess kidneys. Blood bilirubin can rise with extensive red cell destruction. If onion exposure is uncertain, the smear can be checked for spherical red cells suggesting immune-mediated haemolysis. If a zinc-containing metal object may have been swallowed, X-rays can identify this alternative cause.

Treatment

Soon after exposure

After recent exposure, the vet may try to remove onion from the stomach before absorption. A medicine intended for the purpose may induce vomiting. This can be dangerous if the dog is already very drowsy. Activated charcoal's effectiveness in binding toxic allium sulphur compounds is uncertain.

Vomiting is not induced without a swallowing reflex because airway protection is impaired. Activated charcoal can itself raise blood sodium, so benefits are weighed before use.

The vet may consider induced vomiting in an asymptomatic dog within two hours of ingestion. A very weak or hypoxic dog is stabilised first.

Supporting anaemia and kidney function

Life-threatening signs may require oxygen. Severe anaemia can be treated with transfusion. Intravenous fluids aim to protect kidneys from urinary haemoglobin damage.

There is no specific antidote, so treatment supports vital functions. Fluids can also correct electrolyte disturbances when vomiting or diarrhoea has caused dehydration.

Recovery monitoring

The Schnauzer that ate garlic was discharged four days after admission in the published case. Its blood tests showed no significant abnormalities 24 days after discharge.

Transfusion safety

Blood typing before red cell transfusion helps select a suitable product. Vital signs are monitored during and after transfusion to detect reactions promptly. Fever is among the common reaction signs monitored in hospital. Post-transfusion haematocrit helps assess how well anaemia was corrected.

Prevention

Exclude onion and garlic from canine food, including cooked forms. Check ingredients before giving prepared food such as a leftover meatball. Keep powder and dried flakes in an inaccessible cupboard.

Ask everyone at home to avoid onion-seasoned scraps to prevent repeated exposure. Do not add homemade garlic preparations to your dog's food.

Put onion skins straight into a lidded food-waste bin because dogs may scavenge them. If sharing home-cooked food, separate your dog's portion before adding onion.

Important for dog owners

Move your dog away from the food to prevent further eating. Tell the vet whether it was fresh onion, garlic or powder. Estimate when ingestion occurred and how much is missing. Bring the packaging or a photograph of the ingredients. Mention previous exposure if the same food was eaten over several days. Do not give salt to induce vomiting: it can itself cause poisoning.

Keep your dog resting during transport. Report vomiting or unusual dullness immediately by phone. Check other dogs if several accessed the food. Contact a vet for suspected animal poisoning.

Report other illnesses because they affect assessment of the overall condition. If home observation is advised, the vet separately assesses follow-up needs because haematocrit can still fall.

Check which other substances can poison dogs.

Frequently asked questions

Can cooked onion cause poisoning?

Yes: it still contains compounds capable of destroying red cells. Assessment needs the onion content and how much food was eaten. Check ingredients during the call if packaging is available.

Can I wait for symptoms at home?

Contact a vet immediately on discovering onion or garlic ingestion. Dogs may initially appear healthy despite oxidative red cell injury. With recent exposure, the vet can assess whether food can still be removed from the stomach.

What can dark urine mean?

Haemoglobin released from destroyed red cells can pass into urine. For example, the Schnauzer that ate baked garlic developed dark brown urine. Report colour changes immediately because urinary haemoglobin can damage kidneys.

What if my dog ate only leek?

Leeks are also alliums whose oxidising sulphur compounds can damage red cells. Tell the vet which plant was eaten. Mention other ingredients if it was part of seasoned food.

Can dogs recover from onion poisoning?

Dogs eating alliums can recover with appropriate supportive care. Treatment depends on the extent of red cell destruction and severity of hypoxia signs. With substantial urinary haemoglobin, intravenous fluids may protect kidneys.