Medications Routine Dri Tail (Neomycin) for Cavies?

Today when I picked up my two 6 week old piggies - An American Short Hair and American White Crested, I was given Dri Tail Oral Neomycin and was told to add "a couple of capfuls" to their 8 oz. water bottle as this was their routine practice for all guinea pigs they sent home with new owners to avoid diarrhea due to stress from relocating to a new environment. I am to continue it for 5 days. They worried me saying I really needed to do this since if they got diarrhea that was "pretty much it". I understand the seriousness of diarrhea in cavies, but is this really truly necessary to start them off so young on a routine antibiotic? I did go ahead and follow directions on the back of the bottle which is 3 tsp. of the Dri Tail liquid in 4 oz. water bottle with water. Seems that is a haphazard way to get medicated. I don't want to do anything against what might be a preventative, but is this a common practice? Do you feel it is really called for?

They are healthy, active, vocal and eating, drinking, peeing and pooping normally. I have had them for about 10 hours now.

Thank you!