The way we define sacrifice has something to say about that. God killing animals for man's sake can be considered sacrifice due to animals giving their lives for the cause, considering some animals were actually killed, but the word sacrifice would imply preferably to religious/sacred activity. How to separate spiritual life from life as such, when it comes to secure the continuum of the very life itself, without which no spiritual life can emerge?
But even if the killing happened, does it lay out example for the man to follow and imitate? In some things we really ought to do our best to imitate God, like in loving, but in some things it appears so far to be rather complex, like creating ex nihilo sort of stuff.
Clearly, sacrifice for God can be seen as a central element in our relationship with Him, and of course after the lamb of God was slain, the ultimate price has been paid and no one needs to shed blood of another living creature to make it even. We can only sacrifice our ego for His kingdom to come, for our sacrifice to be useful for Him.
For me the concept just jumps in so suddenly without mention in advance that it just made me wonder. I guess it's just one of the things in the Bible we need to take at face value.