Garlic

Common concerns

• Oxidative red blood cell damage (Heinz body and hemolytic anemia) The Merck Veterinary Manual describes sulfur-containing oxidant compounds in Allium species (garlic and onion) as the mechanism behind red blood cell damage. This produces Heinz bodies and methemoglobin within about 24 hours of ingestion, with hemolytic anemia typically developing over the following 3 to 5 days. Clinical signs (lethargy, appetite loss, rapid breathing and heart rate, weakness, exercise intolerance, jaundice, dark urine) generally appear only after substantial red blood cell destruction has already occurred.
• Cats are documented as more sensitive than dogs The Merck Veterinary Manual states cats are the most susceptible species, with toxicosis described in cats from less than a teaspoon of cooked onion or amounts around 5 g per kg body weight of raw onion, while dogs require notably larger amounts (roughly 15 to 30 g per kg of raw onion) before clinical signs appear. Garlic is described as several times more concentrated in these compounds than onion on a comparable basis.
• Concentrated and dehydrated forms carry higher relative exposure Merck Veterinary Manual notes that dehydrated or powdered garlic and onion products (flakes, powders, dry soup mixes) are more concentrated sources of the causative compounds than fresh garlic of the same weight, which is relevant to garlic powder used as a flavoring in manufactured pet products.
• Delayed onset complicates recognition Because oxidative changes to red blood cells occur before outward clinical signs, and hemolytic anemia can take several days to fully develop, a single exposure is not always immediately apparent to an owner, which is one reason ingestion of Allium species is generally discussed with a veterinarian rather than monitored at home alone.