Too much vitamin C per tablet. You don't want to overdo vitamin C, as stopping it can cause pseudo-scurvy. Aim for roughly 30 mg. per day. So if you can find a 100 mg. tablet, you can cut it in fourths, and that will be about right. You'd have to split those tablets into 8-10 pieces, and that's hard to do.
If you're giving them a good quality pellet (KMS Hayloft or Oxbow), a cup or more of veggies that have some high in vitamin C (like peppers), they're fine. Vitamin C supplementation is needed if a pig is ill or elderly, or doesn't have a good diet.
I'm sure you can google up some plain vitamin C tablet that are 100 mg or less.