Sheep production is one of the oldest human agricultural enterprises. Management techniques for improving performance date from the earliest flocks. In the beginning and for hundreds of years, improvements in management were entirely dependent on the observational skill or "eye of the shepherd." Fifty years ago, fall-lambing was limited mostly to Dorset sheep. Range sheep operators wanted only one lamb per ewe. Most of the extra lambs were sacrificed and ewes were not bred before they were 18 months of age. A sick sheep was considered a dead sheep.