We will typically tag ours also within about 12 hrs (weigh it and "paste" it) too. If you wait too long, they are hard to catch (even with a calf katcher - pole like a shepherd's hook). Often with heifers we make sure she has a good bond with the calf before we go messing with it. If it is especially cold out, we will make sure the calf is good and dry - to help minimize any frostbite damage (doesn't always work though). We have used both calf and cow size tags (in the Allflex and Z tag styles). The calf tags are typically cheaper, so if you don't plan on keeping them, you may want to go this route; however, they are hard to read on full grown cows with hairy ears and you will probably want to re-tag them with cow size ones. We have also used cow size ones on baby calves too and ditto to the above (they grow into them). I think all manufacturers make the blank tags (we go this route too). Order the marking pen too - follow the directions by using 2 coats of ink; otherwise, they tend to fade if you don't.
Do beware of the calf bawl (not all of them will do it); but when they do, for our herd we call it "calling all cows" because not just mom comes, but the whole herd of moms come. :shock: For this reason, we don't chance what the mom do and we will "kidnap" the calf (on a 4 wheeler, back of a truck, or inside our Tracker) to tag, weigh and paste - or go put out feed and see that mom goes up and sneak back to work the calf. It just isn't worth getting freightrained (especially if you are doing this by yourself).