Hello & welcome,
Sorry to learn that your dog has been unwell.
I see this as 2 issues which may or may not be related, (clinical presentation & diet).
I am mindful that your vet advised you to go back to the original lower protein food. In hindsight I would have wanted to starve then place the dog on bland home cooked before very gradually feeding lower amounts of the higher protein food brand. That would have possibly allowed you to have better idea as to whether the presentation was likely linked to the higher protein product or not.
Your vet has alleged there can be issues with higher meat & protein content foods, however, you have not disclosed any facts which convince me of a definite link between the specifically named food & confirmed colitis in your dog. There are various causes of colitis in dogs & various tests & work can be performed to try to narrow down the cause. Diet is just one of a number of potential causes of colitis.
Indication is that your dog was placed on antibiotics & advice given to later revert to the original lower protein food....a pretty standard quick fix. It is unclear why you were advised to revert to the original food...It may be vet was guessing re a link to diet or trying to ascertain whether the issue was linked to diet change.
If it were my dog I would reluctantly, (but decisively), switch back to the original (lower protein) food with a view to trying to eliminate possible cause(s). I would monitor stool output & overall presentation of the dog & work with my vet. I would be keen to find out the most likely cause if able.
I would need significant convincing before avoiding relatively higher meat & protein content foods. Ironically my vet only sells a handful of foods, all of which are within the higher protein category & including the one that you have since chosen to be avoid.
Colitis link CLICK here
. I do not know the source & cannot comment re accuracy.
I have prior switched from a specific kibble to firm up stools, however, loose stools are frequently lnked to (often sneaky), scavenging &/or overfeeding...(the later often sorted by minor adjustments to feed amounts).
Bottom line.....I would want dog checked properly &/or stabilised before experimenting with or changing foods.