Chocolate is so popular among people you may wonder if the idea it's bad for dogs is just a story somebody came up with so humans wouldn't have to share it with dogs. In truth, only some chocolate is deadly to dogs; the darker it is, the more toxic.
Chocolate contains an element called theobromine, which is a methylxanthine. Methylxanthine is a compound that causes the heart to race and the muscles to relax. It is found in coffee and other stimulants, such as cocoa. People tolerate theobromine well, evidenced by the popularity of coffee drinks and chocolate candy. The human body is able to easily metabolize theobromine, but the canine body cannot.
Chocolate fudge, when ingested by a dog, can either sicken him, kill him or do nothing at all. Much of the outcome depends upon what kind of chocolate was used in the fudge and how large the dog is who ate the fudge. If the fudge consists of baker's cocoa, the most potent type of chocolate, and a 4-pound dog eats more than 10 ounces of it, death is almost certainly imminent. That same amount of fudge eaten by a Neapolitan mastiff, however, would cause only mild stomach problems, if that. So the size of the dog, along with the amount of fudge and the type of chocolate in the fudge, have a lot to do with how a dog will react. Fudge made without chocolate or with white chocolate is not dangerous. Dark chocolate is most toxic, and milk chocolate is less so.
Because dogs cannot metabolize theobromine, it stays in the canine bloodstream for up to 20 hours. If a dog consumes more chocolate while theobromine is already in the system, the level in the blood can rise to a lethal dose. While even an initial dose of theobromine can be bad for a small dog, in a larger dog it would take several doses, or raising the level in the bloodstream, for problems to occur. Intestinal problems such as vomiting and diarrhea are common. Sometimes there will be blood in the diarrhea due to internal bleeding. A dog that ingested chocolate can suffer seizures and tachycardia, or rapid heartbeat, which could lead to death.
The Merck Veterinary Manual 8th Edition Online reports that while there may be mild signs and symptoms of chocolate poisoning in small dogs who eat less than a half-ounce of of chocolate, more harmful effects may be seen a higher doses, and heart problems and seizures may occur at still higher doses. Their studies show that in most cases, 1 ounce of chocolate per pound of dog is about the rate at which symptoms begin to appear.
If your 40-pound dog has just filched a Hershey's kiss from an Easter basket, don't panic. Remember that the toxicity in chocolate is higher in dark chocolates than it is in milk chocolate. Keep in mind that he may not even become ill from the candy. However, if your smaller dog has raided a tray of brownies, be watchful for symptoms of chocolate poisoning including excessive thirst, restlessness, tremors, seizures, excessive urination, vomiting, diarrhea and inability to control muscle movement.
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