When you give your dog an extra-special treat by spreading peanut butter on top of it or use it to fill a hollow toy, there's no need to worry about the peanut butter going bad if Fido doesn't eat it right away. Peanut butter doesn't spoil the same way many other foods do. But leaving it out longer than a few hours is liable to get you some unwelcome visitors.
Peanut butter is smooth and moist, but since the moisture comes from oils instead of water, spoilage is limited. With a water content that typically falls below 2 percent, there's not enough water to support bacterial or fungal growth -- the main reason food spoils. Leaving peanut butter on a dog treat or in a hollow toy all day -- or for several days -- won't make the peanut butter go bad, and it will still be safe for your dog to eat. That means there's no need to stress about Fido getting sick if he lost the peanut butter treat under the couch and found it later in the week.
Although peanut butter won't necessarily spoil, it won't taste good indefinitely. Exposure to oxygen leads to peanut butter turning rancid, which means the flavor changes in a negative way. This takes a long time, however, often several months. Some peanut butter manufacturers suggest tossing open jars of peanut butter after three months to avoid a rancid taste, but the Live Science website says it can take nine to 12 months for you to notice a taste difference. The peanut butter is safe to eat, although you shouldn't leave a treat out for that long. It's likely the treat covered in peanut butter will spoil before the peanut butter turns rancid.
Leaving peanut butter out for more than a few hours can bring unwanted pests into your home. Even though the treat might be safe to eat, it could attract creatures such as ants and mice if you leave it out overnight. When these pests find the peanut butter, they might decide your dog's food bowl is a bonus and stick around, forcing you to call an exterminator or take other action to rid your home of the pests.
In late 2008, salmonella in commercially produced peanut butter made more than 500 people sick and killed at least eight. Salmonella poisoning can affect dogs, too, but not the same strains. Salmonella isn't caused by leaving peanut butter out too long, though, so there's no danger of introducing the bacteria if your dog doesn't eat the treat right away. Peanut butter contaminated with salmonella would have come from the plant. New safety and testing procedures make salmonella contamination in peanut butter less likely now. If your dog gets sick after eating an old treat, the peanut butter is an unlikely culprit.