Extent and Usefulness of Hybrid Vigor in Animal Improvement

Abstract

The concept of crossing strains and breeds for animal production frequently has been attended by emotional reactions which distract attetttion from the large body of evidence available on this subject. Almost from prehistoric times, one can find many self admitted experts on crossbreeding in animals. For example, in Leviticus l9: l9: "Thou shalt not let thy cattle gender with a diverse kind; thou shalt not sow thy field with two kinds of seed; . . . " But this attitude has not been unanimous, as indicated by Buffon's statement in the eighteenth century: "Only through crossing and mixing of the good qualities present in every animal and in every locality can complete perfection be obtained." But Darwin evidenced a more balanced viewpoint with respect to the concept: "Although free crossing is a danger on the one side which everyone can see, too close inbreeding is a hidden danger on the other." Crosses of distinct genetic groups are made either for direct production of commercial animals, or to develop new seed stocks which will be used eventually as parental strains. The genetic principles involved in the two applications are so distinctly different that the two practices should be considered separately.