Yes you can. Vitamin C is a water soluble Vitamin so in theory you can't give them too much, but they will get the runs if given too much. Ester C is the best and you can get it in powder form. Then you can just to sprinkle it on the food. You can gradually increase the dose until they get the runs and then cut it back a bit. Personally I don't feed the much. I usually just give it a couple of times a week.