you have 3 dogs that you let run for 30-50 min every other daySorry but I don't understand what point you are trying to make. What would it prove to blindly feed any amount of food? If I see my dogs gaining weight and don't make some changes to their diet and exercise that just makes me look stupid.
I am changing foods to improve my dogs health. I don't care what brand of food it is I am not going to make my dogs fat. I am not going to throw common sense out the door based on the brand name on a bag of dog food. Quality nutrition, portion control and exercise are required to keep dogs at a healthy weight and condition.
Due to the oppressive summer heat here in Texas I scale back the amount I feed in the summer and then as the weather cools (soon I hope) I increase the portions for each dog. Currently I am feeding 1 cup to my oldest dog (a spayed female weighing around 45lbs) and 1 1/2 cups to my youngest dog (35 lbs). I would not be surprised for those amounts to double during hunting season.
you are feeding them 3 cups a day
feed them 3 cups of purina pro plan performance at the same time with the same excersize- 3 months later- see if your dogs lost weight
btw- I think my 4 Britt's would die on one cup a day