GM 30. Effects of inbreeding and heterozygosity on preweaning traits in a closed population of Herefords

Abstract

Within an environment, heterosis in a given trait seems to be a function of the genetic differences among lines or groups being crossed. Five lines founded at Fort Keogh Livestock and Range Research Laboratory (LARRL), Miles City, Montana by single Hereford bull. The goal of this study was to estimate the effects of inbreeding during line formation and effects of heterozygosity on preweaning traits of line crosses in a closed population of Hereford. Raw means for birth weight (n=8065), daily gain and weaning weight adjusted to 205 d of age (n=7380). Traits were analyzed by derivative-free REML with the MTDFREML program. The vector of fixed effects included sex: male, female and steer; combination of year of birth (1934-1988) with month of birth (March-June); parity of dam: 1-10 and covariates for the linear effects of direct and maternal line fractions in addition to the direct and maternal inbreeding coefficients and heterozygosity fractions. Mean effects of direct and maternal heterozygosity for all groups were estimated as deviations of the corresponding average effect of heterozygosity from the absolute average of inbreeding depression. Results support the hypothesis that inbreeding depression is due to a loss in heterozygosity that occurs information of lines and that heterosis is basically recovery of that depression.