calf is about 3months still on milk replacer. healthy calf. this is my 3rd calf and this is the first time i saw this happen to any calf. I can retrieve a picture ASAP.
From the pictures...I'd say some kind of parasite. Lice....mange mite??? Not sure...but I bet if you take a skin scrapin in to a vet they could tell you pretty quick. It looks very irritated to me.
Looks like the little bugger was resting his chin on something metal and frozen.... but I'm guessing that didn't happen where you live. Looks kinda like some sort of scald.
Look up BQA (Beef Quality Assurance) guidelines and they will tell you how to administer the shot whether it is Sub-Q or IM. Get BQA Certified, it is easy and will improve your operation.