Your dog's health is very connected to the type of food you feed him...feed him right, add years to his life...feed him wrong, and problems are sure to occur in later years.  Just as humans, most times in our younger years, we think we can 'get away with' a lot of things we do that are abusive to our bodies, we think we aren't affected...only to find later down the road, when we reach our 30's, 40's and especially our 50's we encounter problems from those things we did years back.  Remember, dogs age quicker than we do, signs of improper nutrition can show up in a couple of years.  Once set in, reversing the effects are much more time consuming and costly than taking steps to keep it from occurring in the first place.  That old saying, 'an ounce of prevention is worth a pound of cure' speaks volumes to how we should conduct our lives and the lives of those with us, including our furry companions.
With more shelter and rescue dogs being adopted these days, it's difficult if not impossible to know or try to figure out what is going on with an animal that we know little about.  Because of this we need to make sure when we take on a dog that we know little or nothing about his/her background, that we practice top notch nutrition. adding into that a non-toxic environment.