Mr Underwood says there was slightly more milk in the All Black bottle before the calf made his choice.
The All Blacks have been made favourites by the bookies putting odds of a New Zealand victory at $1.42, with the Aussies at $2.70.
The match is a warm-up for McCow's starring role at the World Cup, when the Herald will use him to predict outcomes of the All Black matches.
Sadly, McCow won't be able to milk a win this weekend - "I don't think he could get any more spoiled than he already is," Mr Underwood said.
All black, except for a silver fern on his forehead, McCow was the cream of the crop from the day he was born.
The young bull has quickly gained a following and has 500 "likes" on his Facebook page.
A victory this weekend will ensure the All Blacks win the Tri-Nations. Now Richie McCaw needs to ensure it's a case of "you beauty" rather than "dairy, dairy me".