INBREEDING AND HETEROSIS IN ANIMALS

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Abstract
How packed with meaning this subject is for animal breeders! And how greatly our understanding of the potential usefulness of inbreeding and heterosis in animal improvement has expanded during the last four decades as a result of the research, writing and teaching of Dr. Jay Laurence Lush! While Dr. Lush was busy at Texas A&M from 1922 to 1930 publishing studies of inheritance and performance evaluation, he must also have been studying Sewall Wright's interpretations of the U.S.D.A. inbreeding and crossbreeding work with guinea pigs (1921). This seems clear from his 1927 paper clarifying the limitations of “percentage of blood” in describing genetic likeness, particularly among collateral relatives and from the subsequent series with his students and collaborators on the amount and kind of inbreeding occurring during breed development in cattle, sheep and swine (1932 to 1936 to 1946), using the technique of Wright and McPhee (1925) for sampling random lines of ancestry. When Dr. Lush arrived at Iowa State in 1930, earlier experiments with full-sib inbreeding in swine at Iowa and elsewhere had been discontinued due to loss of fertility. However, Wright's theoretical analyses and some results with guinea pigs (1921 (1922) had indicated that selection might be able to offset unfavorable effects of milder inbreeding and that inbreeding was a powerful tool for creating genetic diversity among lines. This led Dr. Lush to initiate an experiment in 1930 comparing intense and mild line breeding in pigs, with concurrent individual and progeny test selection. During this same period (1933), Lush's

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