The teams split their two meetings last season. There were a combined 122 and 127 points scored in those games. Expect a similar low-scoring matchup again in today's matchup.
Neither team is used to playing on Christmas Day. This is a very early start time, too. The game is being nationally televised and there will be fans in the stand. I consider all of these factors as additional pluses for an Under. 
Wisconsin is the top defensive team in the Big Ten. The Badgers give up 57.5 points, which is the 14th stingiest defense in the nation. The Badgers have excellent size up front. So I don't see the Spartans getting many second-chance opportunities. The Spartans' leading scorer, Joey Hauser, also is dealing with a sore knee. 
Michigan State should play with tremendous defensive intensity following a lackluster, 79-65, road loss to Northwestern to open its Big 10 season this past Sunday. Tom Izzo called that game one of the worst of his 26 seasons coaching.