Food poisoning in our pets is a bit different than what we expect with people. As with people, it isn't a specific illness, but rather a category of illnesses contracted from eating "bad" foods. Due to their evolution eating raw meat and carrion (before they discovered we had couches!), our pets are generally less sensitive to foodborne illnesses than people. However, they can still get sick from food in ways that present with what we generally consider "food poisoning".
Garbage in, garbage out
Dogs can experience gastrointestinal (GI) issues from eating indiscriminately. "Garbage Gut" refers to diarrhea and/or vomiting resulting from eating food items your pet isn't used to, such as rich table scraps, kitchen garbage, or whatever other feast it might mischievously get into. Such episodes generally result in signs that occur soon after the episode, as the body tries to expel that which didn't agree with it. Most episodes are not dangerous if vomiting and diarrhea are the only signs and the pet is able to keep water down.
If your adult pet has diarrhea and/or vomiting and no other symptoms, it is advisable to provide a bland diet for 24-48 hours to give his system a chance to recover. Rice and plain cooked chicken or cooked ground turkey are good options. Despite debate about whether dogs can eat raw poultry, this is definitely not the time to allow it, as it is more difficult to digest and the already-compromised GI tract is much more susceptible to bacteria in raw meat than a healthy gut. Once you see an improvement in the symptoms, you can slowly start to reintroduce the normal diet.
Post-binge blues and other problems
Keep in mind that depending on the contents of the garbage, it's important to watch for signs of illness in the following days as well, because some garbage contents can cause additional serious problems. High fat foods can cause bouts of pancreatitis, a potentially fatal illness. Also, obstruction is possible from some garbage contents such as corn cobs that can be quickly swallowed but have a hard time moving through the stomach opening to the intestines or through the twisty intestine itself.
Also, just because dogs have "stronger" stomachs than we do doesn't mean they can be a catch-all when you're cleaning expired items out of your refrigerator. Although they don’t get sick as frequently, this doesn’t mean it doesn’t happen at all. It is still possible for them to get sick, particularly when the amount of bacteria in the item is high, which can occur as food spoils. Also, consuming some molds on food can cause serious neurological reactions in both people and pets. Of course, if you know your dog got into rancid food, watch him carefully over the next day or two. Diarrhea or vomiting in such situations is often self-limiting, but if blood is seen in the stool or your pet is unable to keep water down, you should consult a veterinarian quickly.
This advice on feeding and food poisoning applies to both adult dogs and adult cats. But our feline friends tend to be a lot more discriminating than your average Labrador with their consumption, both in type and quantity. Therefore, the vast majority of "food poisoning" episodes occur in dogs. Kitties are generally more prone to chronic (long term) vomiting without an obvious tie to food intake. Chronic vomiting can be signs of general GI or metabolic disease and should be worked up by a veterinarian.
Just like human babies and children, younger pets have not been exposed to the common pathogens in their environments yet, so their immune systems are just learning what germs are out there to fight. During this time, puppies and kittens are more susceptible to illnesses that probably would not cause illness in an adult. Salmonella and E. coli are two examples of foodborne bacteria that can make baby animals very sick. Additionally, a number of viruses can present with GI (gastrointestinal) signs and be very serious for your new pet. Babies lack the reserves to handle vomiting or diarrhea for long and may need more supportive care, such as IV fluids, to get through such illnesses. Therefore, puppies and kittens with vomiting or diarrhea should see the veterinarian immediately no matter what cause is suspected.
When to seek veterinary advice
All cases are different, so it is difficult to specify exactly how long is too long to experience acute gastrointestinal symptoms. Vomiting actual food really shouldn't last more than several hours because either the stomach should be fully emptied (thanks to the vomiting) or because whatever food was in the stomach should have passed into the small intestine. Therefore, if frequent vomiting of actual solid food occurs for more than 8-12 hours, there may be a serious issue. If blood is noticed in either vomit or stool, this can be a sign of internal damage to the GI tract and may potentially be serious. Finally, if diarrhea doesn't improve within three days on bland diet, or if diarrhea isn’t the only symptom, you should consult your pet's veterinarian.
Be aware that more serious and even critical illnesses can initially seem like "food poisoning" to the untrained (and even the trained) eye. Pancreatitis, foreign body obstruction, and Gastric Dilation Volvulus (GDV, more commonly known as bloat) are all life-threatening issues that require veterinary intervention. Additionally, some types of toxicosis (such as antifreeze poisoning) can appear with GI signs. If your pet's GI issues are accompanied by other symptoms such as abdominal pain, vomiting without actually bringing anything up, a visibly swollen belly, restlessness or lethargy, or respiratory difficulty (e.g. continuous panting when it's not hot), there may be more serious cause for concern, and you should consult a veterinarian immediately.