There is nothing wrong with adding salmon oil and probiotics. With that being said for a 12 week puppy don't overdue it. At most I would give 500mg of salmon oil until your pup is 6 months. Probiotics just follow the directions. I use the stuff from purina the name is slipping me, but someone on here will know.
I have had great results with Grizly salmon oil, and it doesn't require you to add vitamin e which is a bonus.
If you are feeding a high quality food, that is usually enough. So your doing it right so far. Sent from my iPhone using Petguide.com Free App