Hello, I have a 6 yr old, neutered male, 40kg german shepherd. He gets average exercise, has a lovely temperament and shiny coat, slim but not skinny.
I’ve had him two years (adopted after his owner’s death) and he has always been fed, like my other GSD, on Applaws large breed. He always poo’d erratically, maybe 3-5 random times daily but the poo was well-formed and OK. About 3 months ago he started getting diarrhoea - going maybe 8 times daily, always runny and smelly. The vet gave a Panacur course and some pre/probiotic paste and recommended we change him to Wafcol Salmon and Potato large breed, which we did. She had never heard of Applaws so couldn’t comment on it, but I see it gets a higher mark (4.8) on here than Wafcol. No allergy test was done as he is vet-phobic and she could barely touch him (which I know is an issue I have to resolve). He had 500g of Applaws daily, split into two meals, and he now has 575g of Wafcol daily, split into two meals.
Six weeks on the poo is now well-formed, but his poo’s are HUGE. He is now going about five times daily, but he is always absolutely desperate to go as soon as we open the door in the morning and is obviously having to hold it in overnight. I’m sure he poo’s out the same volume he eats!
It just doesn’t seem right. Would it be best to go back to Applaws? Or maybe Simpsons 80/20 (which gets a 5.0 on here)? Or stick with the Wafcol in case he is allergic to something? Or other suggestions welcome!
Thanks in advance for any input 
Hello and welcome to the forum. It helps to do a comparison to see if there is a common denominator in these two foods. The reviews are here:
Applaws Adult Large Breed.
Wafcol Adult Salmon and Potato Large and Giant Breed.
Regarding the Applaws, from the history you give it is difficult to say whether it was this that caused the diarrhoea. Overfeeding can cause this but you are quite precise in what you give so we could probably rule that out. There are a few ingredients that may cause problems for some dogs - pea and potato. It also contains cellulose which is fibre and may contribute to the frequent, large poos.
Wafcol sounds as if it is suitable for dogs with digestive issues. In the past I have fed a similar product to this and IIRC my dogs had bulky poos too. Looking back, I am fairly sure it was due to the potato and possibly the pea flour. According to the Directory, Wafcol contains 34% potato. It is possible for a dog to be intolerant of this. My friend’s Labrador was tested positive for this and my own dog doesn’t do so well on it. I find it makes her poos soft. Normally they are very firm.
I can’t say for sure what is going on but as both of these foods were grain free and contained potato, you might want to consider an alternative carbohydrate. This could be sweet potato or rice (brown rice is better). Some grain free foods that contain sweet potato also have white potato. If you use the Dog Food Directory you can exclude potato and pea by using the filters on the left side.
There are some cold pressed foods that don’t contain potato and/or pea but do have brown rice. They are suitable for this kind of problem and might be worth exploring. Gentle and Guru Surf and Turf seem suitable and they both contain particular ingredients that are included for good digestive health - green mineral clay and dried moor.