Crossbreeding is the mating of individuals from different breeds. To a certain extent, it is a simple concept, but embarking upon a crossbreeding program, in sheep or any other livestock species, involves long-term decisions.
The primary benefits of a crossbreeding program are heterosis and breed complementarity.
Aaron, Debra K., "Crossbreeding Considerations in Sheep" (2014). Agriculture and Natural Resources Publications. Paper 156.