Dogs are omnivores and therefore very good at digesting plant foods. In contrast to the wolf, he has a gene that makes starch digestion possible, amylase. If you think back to the end of the 19th century, meat was a luxury good and dogs only got the bone from the Sunday roast. So he was a vegetarian for the most part anyway, and there was nothing wrong with that.
Dogs have specific nutritional needs that can be met with a balanced complete vegan food such as Greta or Pauline, or a home-cooked meal according to our feeding recommendation, completed with V-Complete.
By the way, there are now more and more dogs who react with intolerances to animal protein and thus find an alternative in vegan food.