I feed my little girl Royal Canin and i decided to buy her a Bob Martin pill - it smells like Brewer's Yeast to be honest. it has various other vitamins in it too tho. It's a simple off the shelf pill and she LOVES them!
But when i took her to the vet the other day I asked if it was necessary and he told me that if she is eating a really good food (and he says Royal Canin is great) then she shouldnt need anything extra. I still give it to her but he said if i do it must be the minimum quantity. I find her coat is in great shape from it and her eyes are bright.
From what i read, Preganant bitches and mothers require extra vitamins but if your dog is just like mine then it's an optional extra becasue they should be getting everything they need from their diet
I dont see any harm in extra vitamins, altho too much of anything is normally not good so give it in moderation
picky eaters that they can be, i give mine hers to encourage her appetite!