Slaughter lambs are sold on either a rail grade or a live weight basis. Live weight price is based on the lamb's weight as it crosses the scale. Livestock sale yards are equipped to weigh lambs and sell them on a live weight basis. Ewes and rams are sold on a per head basis. When selling on a live weight basis, the shrinkage of an animal has a significant effect on the final return.
Shrinkage refers to the reduction in a lamb's total live body weight during shipping.
During the first twenty hours, a lamb's shrinkage is mostly loss of gut fill, or stomach contents. After this time, the lamb's body compensates for loss of water by drawing moisture and nutrients from carcass tissue. Before determining the price to be offered, a buyer will estimate the amount a lamb has shrunk either by looking at the lamb or by knowing how far it was shipped. If lambs are to be shipped a long distance, and are weighed before shipping, the shrink may be as high as six or seven per cent. The carcass weight usually ranges from 48 to 52 per cent of the shrunk live weight, depending on age, finish, and wool length of the lamb.