Find a high quality dog food they like, which keeps them in good health. Feed the dog that brand for the rest of their life, unless some metabolic problem occurs at a later age.
That's a myth at least for dogs. Unless the manufacturer has gone out of their way to not include Vitamins, 99% of the commercial dog foods are complete. The only thing you will accomplish by switching, adding/substracting wet food is that you will cause transient shifts in the intestinal flora population. This could explain the differences in smell. More important than smell is to avoid diarrhea, and other digestive problems.I was told that a dog and cat can’t get enough vitamins out of it’s diet if it eats the same thing all the time.
Another myth. A dog's stomach is proportional to its size. Dry food will expand in any stomach. But as long as the dog doesn't gorge itself full, there is no problem. As a matter of course I've always encouraged my dogs not to engage in strenuous rolling type play after eating, in order to avoid stomach inversions. They do well on their dry food.I also have heard that you shouldn’t give Chihuahuas any dry kibbles, because it expands too much in their tiny belly’s.
Depending on age, don't assume dry skin is an allergy. Chihuahuas are prone to Demodex, which can flair up later in life. Also if not done already, have the thyroid hormone levels checked. If that checks out ok, you could try supplementing the diet with a little fish oil.
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