Golden retriever with on-off diarrhea

I have a 12 month golden retriever who seems to have a sensitive tummy. He came to us on The natural dog food company puppy chicken which he never seemed to like. He had a bout of diarrhea that lasted for a couple of weeks and after clear tests from the vet and a prescription diet it settled down. We then slowly changed him on to walker and drake cold pressed and he loved it but was pooing about 8 times a day. He is now on Grace authentic which he loves, he also has a probiotic supplement. He now poos a couple of times a day but they vary from firm to very soft and he regularly (every few weeks it seems) has very runny poo but always seems happy and not unwell. The vet has suggested trying Pro Plan Sensitive but the nutritional value is awful compared to Grace, ideally I don’t want to keep changing food but not sure what to do next.

Hello and welcome to the forum. I am not familiar with Grace Authentic so I have checked the Dog Food Directory and the review is here. It has a 90% nutritional rating. The problem that you are seeing in your dog sounds very much like overfeeding. High quality foods like this one sometimes need to be given in smaller quantities. Do you weigh the food out accurately? If not, it might help if you did this so you know exactly what your dog is getting each day. Natural Kefir can be given as a digestive supplement and it might also be helpful to consider a canine specific probiotic.