Thank you for rescuing
Beneful is probably one of the worst foods
Here are a couple sites to help you rate dog food:
Dog Food Reviews - Main Index - Powered by ReviewPost
Dog Food Comparison, Ratings, Reviews - In-Depth Guide to the Best Dog Food
Dog Food Reviews and Ratings | Dog Food Advisor
A lot of boxers do better without grains (corn, wheat, rice)
You want to read the labels and avoid the "worst of the worst" as I say.
Corn, wheat, "by-products", animal digest(yuck) - google that- it will disgust you!