Murgen,I use boluses in my cows but not on the calves I sell .Boluses cost twice as much but a cow never loses it,just like magnets,they stay put.You were asking Staff about how many are used in North America and probably you should ask Dupont as they make them.I would wager a bet that Australia has the biggest use but I read that Africa uses boluses alot according to storys I found on Google.