Higher reproduction and lower replacement rates lead to a higher proportion of terminally crossbred offspring to sell. Substantial improvement in herd efficiency can be achieved by improvement in the ratio of replacement rate to reproduction rate by selection or crossbreeding. In crossbreeding for surplus reproduction, reproduction from F1 dams may do better than rotational crossbreeding, especially in pigs. Evidence is presented that a strong  enough maternal limitation on offspring size sometimes exists in small enough dams in primiparous animals so that fetal dystocia can be avoided. With a constant slaughter mass, a decrease in breeder limit mass or an increase in feeder limit mass will lead to gain in herd efficiency; if, furthermore, an optimal or maximal feeder-breeder limit mass ratio exists, an optimal feeder limit mass can be calculated for the maximization of herd efficiency.

Keywords: Constant slaughter mass, crossbred reproduction, herd efficiency, meat production