Wyoming and Utah bull moose weighs 750-850 pounds. Moose in the far north tend to be much larger. In Alaska and Siberia they can weigh 1500 pounds or more. The distant from their shoulders to the ground can be as much as 7 feet. Yes, younger bull moose loose their antlers later in the winter because they don't use their antlers as much.
Bull moose use their big racks fighting with another challenging bull moose.
They often loose their antlers soon after fall mating season. After growing their velvet covered antlers throughout the summer, the velvet dries out and becomes itchy. A tree is a great place to rub off the velvet and also lets other moose know that they are around. Its called a dewlap. A long narrow tail of hair grows from the dewlap creating a bell.