Can a Chihuahua eat plain yogurt?
Yes, plain and unsweetened, in small amounts.
How much: 1 teaspoon of plain unsweetened yogurt, twice a week at most.
Why
It provides probiotics. Plain only: sweetened or flavored yogurts are off the table.
Plain yogurt in a Chihuahua's diet
Keep in mind how tiny the portions are for this breed: an adult Chihuahua eats roughly 1 to 2.3 ounces (25-65 g) of food a day depending on his weight, and treats shouldn't go over 10% of his daily calories. That's only a small fraction of an ounce. What looks like "a little bite" to us can be half a meal for him.
This information is for general guidance and is not a substitute for advice from a licensed veterinarian. Every Chihuahua can react differently; if in doubt, always check with a professional.