The basis of crossbreeding in pigs; A review

Abstract

A survey of the different parameters involved in crossbreeding is given following the analysis of Dickerson (1969). The genetic gain resulting from crossbreeding has a double origin: complementarity and heterosis. The practical importance of these two advantages is evaluated in swine. Average individual ( H 1) and maternal ( H M ) heterosis effects on main performance traits are derived from experimental estimates summarized in graphs; the expected fraction of H I and H M utilized in some crossing plans is given. It appears that heterosis accounts for the major part of the gain from crossing in swine. The observed variation between estimates of heterosis for a given trait is analyzed: the effects of sampling variance, specific combining ability of some crosses, heterosis by environment interactions and association between heterosis and parental mean are considered and some illustrations are given. Finally the different criteria used in optimization of crossing between available pig breeds are reviewed. The present trend is to pay attention not only to the final cross but to the whole crossbreeding system, either as static (at demographic equilibrium) or dynamic (transition phase from another system). The first results of such a study with two French breeds are given briefly.