12 common foods that cannot be used as dog food.

Avocado

These fleshy green fruits contain a fungicidal toxin called persin which could give your dog a digestive upset. However, it's the large avocado stone that presents most danger because it could potentially block the gastrointestinal tract, leaving your dog requiring surgery.

Bones

Contrary to popular opinion, bones are bad for dogs. Not only can they potentially choke your dog, they can cause blockages in the gut, intestinal damage and chipped or broken teeth.

Bread dough

The smell of unbaked yeasty bread dough could attract your dog's attention but it should always be kept out of reach. If eaten, the dough could expand dangerously in your dog's stomach, and the fermented yeast could become toxic.

Chocolate

Chocolate and cocoa-based products contain a stimulating substance called theobromine which is extremely poisonous to dogs – the darker the chocolate, the greater the risk. Even a few ounces of chocolate could leave your dog with sickness, diarrhoea, dehydration, and high blood pressure, and the effect is potentially worse in small breeds. If your dog appears restless or agitated and you think chocolate poisoning could be the cause, contact your vet.

Caffeine

Any product with caffeine can have a similar effect on your dog to chocolate and could ultimately damage its heart. So, keep your coffee, teabags and fizzy drinks well away from inquisitive tongues.

Dairy products

Many dogs find it difficult to digest the lactose in milk, butter and cheese because they don't produce enough of the enzyme, lactase. The effects can range from a mild tummy upset to an irritating skin allergy.

Dried fruit

Raisins, currants and sultanas affect different dogs in different ways and scientists can't work out why. However, experts agree that they contain chemical compounds that are potentially very toxic to dogs. At best, your dog could suffer from diarrhoea and vomiting and, at worst, dried-fruit poisoning could lead to kidney failure.

Fresh fruit

Like dried fruit, grapes are highly toxic and should be kept away from your pet. The pips and stones of some fruits (such as apples, plums, peaches and cherries) contain a chemical called amygdalin, which can cause a digestive upset. Large fruit stones are also a choking hazard - particularly among puppies and small breeds.

Garlic and onion

Members of the allium family (including garlic, leeks and onions) contain a substance called organosulfides which could affect your dog's red blood cells – too much garlic or onion (either raw or cooked) could ultimately lead to anaemia. The symptoms take a few days to appear so if your dog appears sleepy and lethargic, head straight to your vet.

Nuts

Nuts are high in fat and should be avoided by dogs but the most toxic of all are macadamia nuts. They can cause vomiting, increased temperature, tremors and a rapid heart beat.

Xylitol

This artificial sweetener is used in sweets, cakes, toothpaste and chewing gum and has a laxative effect on humans. For dogs, though, an excess of xylitol could prove fatal because it kickstarts a rapid release of the hormone insulin. Too much insulin affects the amount of glucose (sugar) in your dog's blood which, in turn, could cause seizures and affect your pet's liver. The symptoms of xylitol poisoning include weakness, vomiting and a lack of co-ordination, and it requires urgent veterinary attention.