When it comes to snakebites, there's no standard formula as to how long it takes for the venom to affect a dog. The vet can administer antivenin serum to your pet to neutralize snake venom.
According to VeterinaryPartner.com, irreversible effects from venom start soon after the dog is bitten, so time is of the essence in getting your dog treated. A dog bitten on the trunk of the body can die within half an hour from organ failure, according to the New York Times, while you probably have more time if he's bitten on his foot. If you're not certain the snake was venomous, don't take chances. A bite by a non-venomous snake, or a dry bite -- a bite without venom -- by a venomous snake won't harm your dog, but you need a vet to examine your buddy.
According to the website PetMD, there aren't good statistics on the numbers of dogs killed by snakebite annually because there's no central data source for this information. It cites a long-time veterinarian practicing in snake country who estimates that approximately 20 percent of dogs bitten by certain venomous snakes die.
The amount of venom that just causes swelling and discomfort in a large breed dog can kill a little pooch. Larger poisonous snakes usually inject more venom in a bite than smaller species. A large snake biting a small dog means that, based on body weight, little dogs receive higher amounts of venom.