Galdom - it looks as if the PPRune 'bon mots' of "and there'll be plenty of experts to answer any questions." have failed you. I think the answer is no-one actually knows apart from the crew and Auckland ATC. There could be several reasons, but sheep at 3000' during a go-round I have not come across before, not even in NZ.My three 'favourites' would be a little short of fuel, weather or conflicting traffic.You did post the query in the correct forum, and you never know, you might get a serious answer some time. Good luck.