According to European law, 'meat and animal derivatives' is defined as "All the fleshy parts of slaughtered warm-blooded land animals, fresh or preserved by appropriate treatment, and all products and derivatives of the processing of the carcass or parts of the carcass of warm-blooded land animals".
Clearly this is very loose and does not provide any clues as to what parts or even what animals are being used.
It must be said that the presence of this ingredient is not necessarily a bad thing as it encompasses all meats, from the very best, to the very worst. For example, some producers of good foods use broad terms like this in order to not give away their 'secret formula' and some imported foods list very high quality meat as 'meat and animal derivatives' simply because the laws or customs in their home country are different. At the opposite end of the scale, the term can be used for very low-grade animal products including some that are nutritionally very poor. Also, because the species isn't specified, manufacturers are able to change their meat source between batches depending on what is available at the time.
The problem with broad, vague terms like this is that you just don't know. Where you do see it, make sure it states what animal it comes from, and ideally what parts of the animal. If your dog is prone to food intolerance, it is certainly wise to steer away from meat and animal derivatives and all other non-specific ingredients.
Find foods containing Meat and Animal Derivatives See the full Ingredient Glossary