Pet owners want the best when it comes to feeding their four-legged friends. And with so many dog food choices–From fresh to freeze-dried and everything in between, how do you even know what’s best for your pet? 

A new Consumer Reports investigation of popular dog food brands reveals what’s in that food might not always be what you think you’re feeding Fido. 58 dog foods were chopped, blended, tested, and analyzed to answer a simple and important question: Is the food you’re feeding your pooch safe?

In CR’s investigation, we tested popular brands like Blue Buffalo, Hill’s Science Diet and Purina for nutrients and contaminants.

Consumer Reports science writer Kevin Loria says while most brands met basic nutritional standards, Consumer Reports’ testing found potentially dangerous bacteria in some raw dog foods. CR found Listeria monocytogenes, which can be dangerous to pets and even more so to people, in a sample of Raw Bistro’s Free Range Chicken Entree and a sample of Viva for Dogs Ground Beef meal–both frozen raw dog foods.

Raw Bistro says its internal testing showed no contamination, and the tested batch has since expired and is no longer being sold.

Viva for Dogs told CR it has continued to evolve its systems with more robust finished product testing.

CR’s investigation also found that one product, Pedigree’s Complete Nutrition Adult Roasted Chicken, Rice, and Vegetable, contained nearly five times the recommended maximum of vitamin D. Too much vitamin D can be toxic for dogs. It’s crucial that manufacturers stay within safe limits.

Pedigree has not responded to CR’s request for comment.

Bottom line: Experts say the best approach is working with your veterinarian to choose the food for your pet’s needs. In general, look for foods labeled as meeting standards set by the Association of American Feed Control Officials, which recommends nutritional guidelines for dogs and other animals. Limit calories from treats to just 10% of their diet. Don’t switch foods without a good reason. And be especially careful with raw diets — as CR’s tests confirmed, those foods can carry serious risks.

For a complete list of CR’s findings that you can download and take along when shopping, click here.