When we adopted our Lab from Blue Cross she was ten months old, on Science Plan, but had very loose stools. Other makes were gradually tried, but still loose poos. Our vet recommended James Wellbeloved Lamb and Rice, and fortunately it has worked really well with the dog passing two well-formed stools nearly every day since. (A year.)
Having read all this thread, I have learned a lot, reactions of the dogs seem to be different, but I am reluctant to change to cheaper food except for good reason. The only down side has been, she has tired of it a bit, and to encourage her we have added a little bit of cooked meat to the middle of the bowl, which she eats first with some of the meal, and the remnants we stuff in a Kong with a dash of peanut butter which she loves and finishes. Someone might tell me this is not recommended, but it seems to work!