Combining Abilities for Size of Linecross and Linebred Holstein Heifers

Abstract Influences of additive and heterosis effects upon body weight estimated from forechest girth and several other body measurements of linebred and linecross Holstein heifers were investigated. The numbers of heifers measured at various ages ranged from 580 at one month to 390 at 19 months. Heifers resulted from prior development and crossing of six lines producing six linebred and 21 linecross progenies. Linecrosses exceeded linebreds in all but one case and usually to a statistically significant degree. This increase, however, varying from 3% for weight to less than 1% for some other measurements tended to be smaller than a hypothetical inbreeding depression of the linebreds based on their average inbreeding of 13%. Generally other effects (line heterosis, specific heterosis, sire line, and sire within line) were not statistically significant.