Domestic dogs have fairly strong prey drives that inspire them to chase all sorts of things that move, including insects. If your dog catches and eats a cockroach, or even decides to eat a roach that is already dead, it is possible -- though unlikely -- that he will get sick as a result.
According to the University of Kentucky, cockroaches are the most common type of insect found inside American homes. Types of roaches commonly found in the United States include German cockroaches, American cockroaches, Oriental cockroaches and brown-banded cockroaches. They like to live in damp, warm areas and are able to survive in a wide variety of climates. Roaches will eat almost any type of substance, including wallpaper paste, clothing and paper.
Roaches are not poisonous in their natural state, and they do not contain toxic ingredients. In some cultures, humans voluntarily consume roaches as a delicacy. Your dog will not be instantly poisoned by eating a normal, healthy cockroach. Some dogs may experience an allergic reaction due to consuming a roach, but it is not common.
While roaches are not naturally poisonous, humans spend lots of time and money purposely poisoning roaches every year. Roach poison is toxic, though the dosage required to kill a cockroach should be too low to seriously harm your dog if he eats a poisoned roach. If your dog makes a habit out of eating poisoned roaches, he could build up enough of the poison in his system to sicken him. You do not want your dog to eat roaches that have been exposed to pesticides. If you have pets, it is always a good idea to talk to your exterminator about the types of products used to kill roaches in your home. Ask your exterminator to help you find a method of killing roaches that will not harm your dog.
Roaches carry many diseases that can sicken both you and your dog. Roaches are known for harboring bacteria including salmonella, clostridium, streptococcus, coliform and staphylococcus. When your dog eats roaches, he is exposed to bacteria which can potentially land him in the veterinarian's office. It will be almost impossible for you to know if your dog became sick due to the roach he ate or if his illness has another cause, but the potential for illness should be sufficient reason for you to prevent your dog from eating a roach if you have the opportunity to do so.