The fact is that barley offers a lot of nutritional value to humans and animals, including dogs. As long as it is good quality barley, it will not be bad for them in the slightest. They are considered to be fillers and not bad for your dog. Although it is true that barley isnâ€™t bad for them, they can be allergic. There are certain breeds of dogs which are more prone to barley allergies than others, so you will want to do your research before giving your dog anything with barley in it. If your dog does have a barley allergy, it is likely that they will simply throw up the food or have some other type of adverse reaction.