This is a jukugo word, which usually means on'yomi readings from the kanji. Since 大 has two on'yomi readings, here's a mnemonic to help you remember which one to use:
You've been assigned the important task of taking care of the local tie yaks (たいやく). Where you're from, tie-wearing yaks are incredibly important, so don't take this great duty lightly!
I will try with all my might to successfully accomplish this important task.
You volunteered for such a great duty, eh?
Frodo, of the Lord of the Rings, was given the most important task and he did it all without putting on shoes.