A question of pH in the stomach and digestion time?
One of the main arguments against the kibble/raw meat mixture is that the stomach pH of a dog fed with kibble is less acidic than a dog fed raw meat. This too high pH would not allow it to properly digest raw meat and bones, nor to get rid of any pathogenic bacteria present in raw meat. A dog fed in this way would therefore be more exposed to food poisoning.
The other justification for this belief is that there is a different digestion time between raw and cooked.
Studies that contradict these beliefs
Several recent scientific publications go against these beliefs by reporting a very low stomach pH in dogs fed with kibble, a pH which would therefore also make it possible to digest raw meat and bones which go through it at the same time and play a protective role against bacterial contamination (all things considered and if the meat is of good sanitary quality, of course).
As for the digestion time, it does not only depend on the cooked or raw character of the food that the dog ingests. It is influenced by various factors including the digestion time such as the size of the pieces of food, the volume of the meal, the amount of lipids in the food, their water content, their soluble fiber content etc.
The role of the stomach is precisely to mix foods, sometimes different, in order to constitute an acid porridge, called chyme, which will be poured into the small intestine to continue digestion.
So can we mix raw and cooked?
The answer to this question is therefore "yes, without any problem" . In the same way that you eat a green salad with a steak, you can therefore mix raw meat with cooked foods such as croquettes in your dog's bowl within the same meal. You can also give him a meal containing raw meat in the morning and then kibble in the evening (or vice versa) without the risk of disturbing his digestion.
The only precaution to take, when practicing mixed food for your dog, is to introduce foods that the animal is not used to eating gradually in its diet by respecting the principles of food transition.