Dr Liesel van der Merwe is a small animal medicine specialist. Send her your questions: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Dr Liesel van der Merwe

Current understanding of adverse food reactions in dogs and cats generally relies on human-based information. Adverse food reactions are generally classified either as a food allergy or food intolerance and cause wide-ranging symptoms in people, with several diseases having known dietary causes.
The prevalence of adverse food reaction in companion animal species is unknown, but food intolerance and dietary indiscretion are generally considered more common than food allergy.

The main causes of food intolerance in dogs and cats include specific ingredients, additives used during food manufacturing and the effects of microbial spoilage. Food-borne illness is difficult to diagnose in veterinary medicine due to the lack of available diagnostic tests and the dose- and species-dependent nature of symptoms. Early symptoms may occur hours to days after food consumption and can last for several days, further complicating the diagnostic process.

Bacterial spoilage rarely causes food-borne illness in otherwise healthy dogs and cats, because they are considered relatively resistant to pathogenic effects from bacteria. This makes sense if you consider the scavenging nature of carnivores, both domestic and in the wild. Dogs and cats are also more resistant than humans to toxins produced by pathogenic gut bacteria.

Companion animals are, however, highly susceptible to aflatoxicosis due to  Aspergillus  contamination of grains and legumes, and dogs are also particularly prone to tremors and seizures after eating food contaminated by the Penicillium mould.

Bacterial contamination of oily fish, such as anchovies, tuna and sardines, can cause scombrotoxin poisoning, which is characterized by severe gastrointestinal (GI) signs occurring within 30 minutes of ingestion. Both dogs and cats are susceptible to scombroid, which is also the most common cause of seafood poisoning in humans.

Few studies have addressed the toxic effects to pets from additives introduced during food manufacturing. Although the preservative benzoic acid is linked to atopic dermatitis in humans, its effects have not been documented in dogs or cats.

Another additive, propylene glycol, may cause Heinz body formation and reduced red blood cell survival in cats. Cats have especially sensitive red blood cells and they are prone to oxidative damage. Even normally, their red blood cells have a shorter lifespan than those of dogs (78 days versus about 100 days).

Use supplements with great caution in dogs and cats, because safe upper limits have not been established for many nutrients. Adverse effects have been reported after excessive administration of dietary vitamins A and D in cats and dogs, respectively.

Methylxanthine toxicity is well known in dogs and cats from ingestion of caffeine or theobromine. Caffeine is found in tea, coffee, soft drinks and some human medications. Pets may encounter theobromine in both likely (such as chocolate) and surprising (such as garden mulch) sources. Because theobromine is eliminated slowly, clinical signs can persist even after ingestion of small doses.

Methylxanthine toxicity is associated with restlessness, polydipsia and GI signs that may progress to serious neurologic signs, cardiac arrhythmia and respiratory failure. The darker the chocolate, the higher the concentration of theobromine.

Xylitol, a common artificial sweetener in many human foods as well as in medical and dental products, is highly toxic to dogs. This sugar alcohol stimulates insulin release, which can result in a severe drop in blood glucose levels, seizures and liver failure.

Lactose intolerance is common in dogs and cats. Lactase activity in the small intestine naturally decreases in puppies and kittens after weaning, so these patients become partially or completely unable to digest this sugar. Lactose-intolerant patients typically experience bloating and diarrhoea.

Alternatively, pets that cannot tolerate milk may be unable to digest the main protein, casein. Diarrhoea has also been linked to ingestion of several other carbohydrates found in human foods, including the popular artificial sweetener sorbitol and the main carbohydrate found in beans, raffinose.

Organosulfoxides contained in alliums such as onions, garlic, leeks and chives are toxic to dogs and cats in both cooked and uncooked forms. Affected patients typically exhibit GI signs progressing to weakness, pale gums, jaundice, dark urine, increased heart rate and breathing.

Hops, an ingredient used for brewing beer, can cause hyperthermia, increased heart rate, panting, vomiting and seizures in dogs and cats. Grapes, including dried forms such as raisins and sultanas, can cause GI signs and renal failure in dogs if eaten – why some animals are susceptible and others not, is not known.

Many plants, including spinach, rhubarb and beetroot, contain high levels of oxalic acid, which binds minerals and can cause formation of calcium oxalate bladder stones.

Thus you are what you eat . . . and don’t treat your dogs or cats like humans. They have a different metabolism to us. Make sure what you feed them does not cause any harm.

Source: DVM 360