different intestinal ratios for different animals,,
get the small animal 15g syringe. buns will usually eat it right out of the tip of the tube,, it's like snack-pak pudding for them. 1g every other day while on ABs

my buns will eat it like candy.
i accidentally ordered the bird version by mistake, the vet told me to throw it out.

I would call up the vet and ask. Better to be safe.

I emailed PetAg the makers of Bene-Bac and this is what they responded about if its safe to use.

"Good Afternoon,
Thanks for contacting PetAg about our Bene-Bac® products for use on your rabbit. All of our Bene-Bac Plus for any size mammal is the exact same product, just different labels to reach different markets. We even package Bene-Bac Plus in a 30 gram syringe and label it for either equine or zoo animal use!! The “Plus” is in all Bene-Bac products now. The Plus is the addition of prebiotics (FOS) which is the carbohydrates the “bugs” exist on to make it through the intestinal tract."

Well, That makes sense, given as it is essentially Yakult for animals I can't see how they could alter the strengths other than by volume.
I mean you can only have so many Beneficial Bacteria in a mil of suspension fluid.