The more I think of it, I still see no real ethical dilemma or choice either way here.
Cool that you shot the baby., and to Bonecollector's point, you did the calf a favor by ending it's apparent suffering more quickly than would have otherwise. It was hurting, and it was a legal animal. On the other hand, had you passed on the baby and killed the cow, honestly for me that would have been just fine, too. That baby became injured somehow and nature & the way of things were running their course (with or without you). I see no moral/ethical obligation to shoot or not shoot the baby either way in this case.
(But obviously this is TOTALLY my own opinion only, and we all know what they say about opinions..... As I said earlier, good show!)