We are tagging at birth this year. It is the first time we have done it. In the past they have been done a bit older. I have tagged almost 800 lambs now, and have two with infections around the site of tagging. I am fairly sure that is less than we have normally, but still two more than I want. It does seem awful putting the huge tags in the tiny ears, but they are hardly reacting at all, definitely less than when they are a bit bigger. So I THINK I prefer tagging at birth, but I could still change my mind!