I had a case that came up the other day that I hadn’t seen for a while so I thought I had better remind you about it too. I received an out-of-hours call from an owner whose dog was suddenly weak in the hind limbs and seemed more tired than usual.

I met them at the clinic because it sounded serious and in further conversation it turned out that the dog had eaten a whole onion two days earlier, which they soon afterwards vomited up.

A red flag shot up in my brain as onion toxicity can be nasty and here is why.

Onions are part of a group of plants called alliums, which are all toxic to dogs. Garlic, chives and leeks are all also alliums. All parts of these plants are toxic to dogs, even when cooked or dried.

Alliums are thought to contain toxins called disulfides and thiosulfinates that cause damage to red blood cells. This can lead to anaemia, which in turn causes weakness and lethargy as the oxygen carrying capacity to the muscles is reduced.

Some dogs are more sensitive to onion and garlic poisoning than others. Luckily for my emergency dog, they vomited up the onion quickly, so they ingested less of the toxin. We popped her on to fluids and ran some blood tests and thankfully she made a good recovery.

Remember that onions and garlic can be found in many pre-made foods, such as pasta sauces and baby food, so you must be careful when feeding human food to pets, even if they are just licking the plate.

I also hear owners occasionally ask if they should use garlic to treat for fleas. There is no evidence that garlic is an effective flea control treatment (despite what Dr Google says) and the toxic side effects can cause real damage to your pet. Ask your vet for effective and safe flea-control products.

I’m always intrigued by the species-specific differences between animals, including humans. Why can we digest onions and garlic but dogs and cats cannot? Why do certain medications affect different species differently, causing different end results?

Luckily, vets are trained in seven distinct species and their physiological differences, so we are really the best people to advise on good diets, healthy lifestyle and correct medicines. What is good for one species is often not good for another and the internet, despite its many advantages, can also be misleading.

Having a knowledgeable vet who knows your animal’s history and lifestyle, working with an attentive owner goes a long way towards a happy and healthy pet.

• Lucy Richardson graduated from Edinburgh University in 2005. She started CedarTree Vets in August 2012 with her husband, Mark. They live at the practice with their two children, Ray and Stella, and their dog, two cats and two guinea pigs. She is also the FEI national head veterinarian for Bermuda