Many people frequently include onions and garlic in their day to day cooking, however it is important to remember that these foods can easily poison cats and dogs. In fact all Allium species of plants can be involved in the poisoning of pets and the most common types involved are onions, garlic, leeks and chives.
Onions and garlic, along with similar plants contain chemicals called organosulfoxides. These chemicals are responsible for the particular odour and taste which are characteristic of these plants. Such chemicals are readily absorbed through the gut when the plant is eaten, and in animals they, or their metabolites, can then cause oxidative damage to the animal's red blood cells. This is often serious enough to cause the destruction of the red cells - a process known as haemolysis. This can result in haemolytic anaemia if large numbers of red cells are destroyed. Haemolytic anaemia is a serious condition.
Cats are more susceptible to this type of poisoning than dogs (because the haemoglobin in their red blood cells is more susceptible to oxidative damage), but they are perhaps less likely than dogs to consume these plants and their bulbs due to their more fastidious eating habits. Any type of onion product can cause problems for pets including fresh, dried, whole or chopped material, the juice, powdered onions and garlic etc. It does not make any difference if the food has been cooked or not.
Poisoning usually results from pets consuming a large amount of onion or garlic product in one go, or after repeatedly eating smaller amounts at regular or frequent intervals. The quantities of onions consumed does not need to be particularly large; for example, onion poisoning can occur after the consumption of as little as 150g in a 10kg dog.
Signs of onion poisoning may occur within 24 hours of consumption if a large enough amount has been eaten, but it is more common for signs to develop over a few days. Dogs and cats may become depressed, weak, or anorexic. They may have diarrhoea and abdominal pain. Sometimes the owner may notice that the animal's breath smells of onions or garlic, especially if the food was recently consumed. The main problem which this type of poisoning causes is haemolytic anaemia, which is basically the destruction of the animal's red blood cells; however it may be difficult for owners to recognise the specific signs of anaemia in their pets.
If you believe that your dog or cat may have eaten onions or garlic in more than very small quantities and could be poisoned, then you should take your pet along to a local vet quickly. The vet may be able to make your animal vomit if the food was consumed fairly recently and has not yet passed through the stomach. They may then be able to give activated charcoal to help absorb the poison if this is felt to be necessary. Supportive care such as i/v fluids and even blood transfusions may be required for the very sick patient and they will need careful monitoring until they are fully recovered.
As with all potential toxins it is always better to prevent the problem in the first place rather than attempt to treat it following exposure. So, if you use onions and garlic in your cooking please do be careful about feeding your dogs or cats the table scraps and left-overs.