Is fiber important in dog food?

[pacificrules]

We need to switch our choc lab's food to rule out food allergies. Our vet suggested getting salmon based food. I found three at our local pet supply store that I'm interested in. One has 8% fiber whereas the other two have 3%. Is this significant enough of a difference to get the one with 8%? The numbers for %protein, fat, and fiber are:
Brand A: 25/15/3 ($49 for 30# bag)
Brand B: 40/20/3 ($73 for 30# bag)
Brand C: 23/10/8 ($57 for 28# bag)

[dirtyred]

I don't think it's a huge difference; generally, dogs don't need fiber like we do. The harder the poop, the less anal gland issues we have.