Yes
Feeding onions and garlic to your dog or cat is not only bad for their health, but is potentially fatal for your pet. It's not just onions or garlic, there are manybut the whole category of plants that fall into this category of onions,under the botanical name Alliacea, which are listed (see table below).
Onion, garlic, and many variegations of the onion plant contain sulfoxides and disulfides, - onion itself has higher concentrations. These chemicalchemicals cause the red blood cells in cats to break up, which can result in hemolytic anemia. This type of anemia can make a cat fatigued, affect a cat's physical and mental performance and is potentially life threatening; the condition is known as allium toxicosis.
If this type of poisoning occurs there is nothing that can be done to reverse the affects,effects; only the symptoms can be treated; affectedtreated. Affected animals may be treatedtreated with intravenous fluids and may require blood transfusions.
It's important to note the signs of toxicosis may not surface for several days after the animal has ingested the offending food.
If your petspet has eaten onions in any food, please monitor your pet and if any symptoms, like vomiting, or diarrhea, develop or your pet seems unwell over the following few days, seek the medicalveterinary attention of your veterinarian.
Common sources for pets ingesting these toxins are onion plants, table scraps, garbage cans, and manufactured food made for humans, including baby food.
The signs of toxicity are:
CLINICAL SIGNS
In dogs and cats, clinical signs of Allium species toxicosis may appear within one day of consumption if large amounts of material have been ingested. However, it is more common the[to see] the development of clinical signs after a lag of several days. The first signs are usually of gastroenteritis: vomiting, diarrhea, abdominal pain, loss of appetite, depression and dehydration. It will take a few days for the dog to display the signs associated with the loss of red blood cells: pale mucous membranes, rapid respiratory rate, difficulty to breathe, lethargy, dark colored urine (reddish or brown), jaundice, weakness, and rapid heart rate. Depression, hemosiderin in urine, exercise intolerance and cold sensitivity may also be observed. In cases of recent ingestion, the breath of the affected dog or cat may smell like onions or garlic. (1)
A full list of the plants associated with allium species toxicity is here:
table courtesy of Allium species poisoning in dogs and cats, Salgado BS, Monteiro LN, Rocha NS (1)
Note: these remain harmful after being cooked.
Cooking or spoilage of Allium species does not reduce their potential toxicity. (2)
References:
Allium species poisoning in dogs and cats
Salgado BS, Monteiro LN, Rocha NS PDF (1) ISSN 1678-9199 | 2011 | volume 17 | issue 1 | pages 4-11 The Journal of Venomous Animals and Toxins including Tropical DiseasesFoods that are dangerous for your cat
VCA Animal Hospitals(2) Alliumspecies poisoning in dogs and cats R.B. Cope, BSc, BVSc, PhD