Not sure about the grass-eating, but I would like to point out that Beneful is a truly horrible food. Not only is it low on meat and high on grains, it actually contains sugar! Here are the ingredients of Beneful Original dry:
Ground yellow corn, chicken by-product meal, corn gluten meal, whole wheat flour, animal fat preserved with mixed-tocopherols (form of Vitamin E), rice flour, beef, soy flour, sugar, sorbitol,.... added color (Yellow 5, Red 40, Yellow 6, Blue 2),
You might want to find a food that actually has meat as the first ingredient and doesn't have so many carbohydrates or food colouring. Here is some info on choosing a dog food: http://www.dogfoodproject.com/
and a list of ingredients to avoid: http://www.dogfoodproject.com/index....badingredients
Also, the bones you feed are raw, right?