Onions are not so nice

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Now that Christmas is over, back to blogging!

I know I seem to be focusing a lot on poisonings in these pages, but there are so many that come our way. Some poisonings are quite unusual and unexpected and without a little guidance, many pet owners may be putting their pets at risk without realizing it. I mean who would have thought the average Australian backyard BBQ could be a dangerous place for the family dog and cat!

Not only can those fatty off cuts and cooked bones cause trouble for your dog (or the overindulgent cat), but the humble bit of barbecued onion could cause some serious disease in your best friends. Fried up on the barbie with all the fats and flavourings, it is not surprising that a dog might find onions a tasty treat. And while cats generally do not tend to eat the extraordinary, I recently saw a cat who found his mother’s chili con carne quite appetizing and had eaten a good chunk of onion mixed in with the rich chili flavouring.

Onions and their associated family, which includes garlic, are actually quite a toxic plant, not only to dogs and cats, but to humans as well. At least they would be if we ate enough of them but our red blood cells are fairly tough in comparison to those of our pets. Cats have the most fragile red blood cells of any animal and regularly burst them in response to illness and disease, so they very sensitive to the toxic effects of onions and garlic.

The toxic principal in onions and garlic is an alkaloid disulphide that acts on the red blood cells and interferes with their normal metabolism causing Heinz bodies to form (nothing to do with baked beans!). Red blood cells don’t cope well with Heinz body formation and will swell and burst, causing the animal to become anaemic. The following website has a great description for anyone who is scientifically minded: http://cal.vet.upenn.edu/projects/ poison/plants/pponion.htm. Garlic tends to be more potent than onion and the powdered form of both is even more potent than the fresh product. Powdered onion is often found in baby foods, and cats may be poisoned from eating your little one’s left overs.

How much is too much? This will vary from animal to animal as with any intoxication. Everyone has heard stories of friend’s animals, or even their own, who regularly eat cooked onions with no trouble, or who get garlic supplements as a preventative for fleas (not a treatment I would swear by!). The toxic dose recorded in the literature also varies but tends to be in the range of 5g/kg for dogs and less for cats (the average large onion weighs about 200g). Clinical signs will not become evident until sufficient red blood cells have been damaged. Cats may become sick after eating as little as a teaspoon of onion.

Signs that suggest your pet has eaten too much of the left over onion can take between 6-24 hours after exposure to develop and this generally depends on how much of a toxic dose they have eaten. Animals can generally deal with a low grade anaemia but once the red blood cell concentration drops to a critical point, the animal may start to pant more and tire more easily. They will be weak and have rapid pulses, pale gums and may start passing dark urine as a result of the breakdown pigments in red blood cells. The signs develop because the animal can no longer carry enough oxygen to the vital organs for normal functioning so the heart and lungs start working harder and energy levels drop.

What to do? Well, if your cat has eaten any onion or your dog has eaten a questionable amount, the first thing to do is to empty their stomach and clear out their system. Taking them straight to see your veterinarian or an emergency practice is the safest approach, especially with cats, who may require special drugs to make them vomit. Once the stomach is emptied, a good dose of activated charcoal will help to bind any onion toxins left behind in the gut. Other supportive measures may include intravenous fluids and monitoring in hospital depending on various findings that concern your vet. One important tool is to monitor the animals red blood cell volume (PCV – packed cell volume). If this is noted to drop over the following 24 hours, your pet may need a blood transfusion depending on how low it gets and how your pet copes with the drop.  Close monitoring will be required for the next few days while the body begins to rebuild its red blood cell stores.

It is important to really consider what we are giving our pets when feeding them from our table. And it is not just what we give them, but what they can access. I have recently seen a couple of dogs for onion ingestion after an owner came home to find one (or both) had jumped on the kitchen bench and nearly devoured a whole raw onion! Does not sound very tempting, but discretion is not a strong point for some animals!

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