Supply is decided two years earlier. An animal finishes when it finishes, so orders have to be gathered around a slaughter date rather than the date being moved to suit demand.
A carcass is not a catalogue. One animal produces a fixed amount of fillet and a great deal of mince, so selling by the box works and selling by the cut leaves a freezer full of what nobody asked for.
Every movement is recorded by law. Births, movements, treatments and withdrawal periods belong to a register that an inspector can ask for, and reconstructing it afterwards is not an option.
Orders and carcasses have to meet. Knowing how many boxes are promised before the animal goes is what decides whether the farm is short or storing beef it has not sold.