I was looking in this forum to see if there are any views on this. my local France vet said supplements are not recommended anymore since dogs took too much calcium in years gone by and had later problems due to too fast growth. however, when a puppy is not eating, one worries, and i have ordred some suggested found in Poland. Any views welcome ...i agree calcium should be careful with, but vitamin B and fish oils are not dangerous i do not think.
http://serenus.istore.pl/pl,product,1074663,mikita,rumen,tabs,100tabl,dla,psa.html

It is recommended not to add any form of supplement to a complete food, as the food has all the requirements all ready added i.e. it is 'complete'.   Overdosing with certain other vitamins can also have undesirable effects.

Here is a link for you with all the benefits, toxicity etc., of vitamin supplementation.

http://www.dogfoodproject.com/index.php?page=vitamins