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United States Department of Agriculture

Agricultural Research Service

Title: Genetic Parameter Estimates for Yearling Scrotal Circumferences and Semen Traits of Line 1 Hereford Bulls

Authors
item Kealey, C - MONTANA STATE UNIV
item Macneil, Michael
item Tess, M - MONTANA STATE UNIV
item Geary, Thomas
item Bellows, R - RETIRED ARS

Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: May 15, 2004
Publication Date: June 15, 2004
Citation: Kealey, C.G., Macneil, M.D., Tess, M.W., Geary, T.W., Bellows, R.A. 2004. Genetic parameter estimates for yearling scrotal circumferences and semen traits of line 1 hereford bulls. Western Section of Animal Science Proceedings 55:36-39.

Interpretive Summary: Bull fertility can only be directly measured by the production of a calf crop. However, this measurement is impractical because establishing fertility before the breeding season as opposed to after the breeding season is required to insure maximal reproductive success. Traits indicative of fertility have been identified. Therefore, the objectives of this study were to estimate heritability of scrotal circumference and semen traits, and genetic correlations between these traits and birth weight. Heritability estimates for birth weight, scrotal circumference, volume, concentration, motility, and percents normal, live, and primary and secondary abnormalities were 0.46, 0.57, 0.09, 0.16, 0.22, 0.34, 0.23, 0.09, and 0.13, respectively. Estimates of genetic correlations between birth weight and scrotal circumference, volume, concentration, motility, and percents normal, live, and primary and secondary abnormalities were 0.36, 0.07, 0.58, 0.21, 0.20, 0.34, -0.25, and 0.05, respectively. The moderate heritability estimates for scrotal circumference and several of the semen traits evaluated, imply improvement in these traits can be achieved through genetic selection. The genetic correlations between birth weight and semen characteristics indicate that there may be some negative impacts on bull fertility if selection for low birth weight is practiced.

Technical Abstract: Objectives of this research were to estimate heritabilities of scrotal circumference and semen traits, and genetic correlations between these traits and birth weight. Line 1 Hereford bulls (n = 841), born in 1963 or from 1967 to 2000, were selected either for use by USDA-ARS at Miles City, Montana or for sale. Semen was collected by electro-ejaculation when the bulls were approximately one year of age (mean = 446d) and all samples were evaluated by one person. Traits analyzed were scrotal circumference, volume, concentration, motility, and percents normal, live, and primary and secondary abnormalities. Primary abnormalities were abnormal heads, abnormal mid-pieces, and proximal droplets. Secondary abnormalities were bent tails, coiled tails, and distal droplets. Data were analyzed using MTDF-REML. The model included fixed effects for contemporary group and age of dam, covariates for age of bull at evaluation and inbreeding of the bull and his dam, and random animal and residual effects. Random maternal effects were also included for birth weight. Heritability estimates for birth weight, scrotal circumference, volume, concentration, motility, and percents normal, live, and primary and secondary abnormalities were 0.46, 0.57, 0.09, 0.16, 0.22, 0.34, 0.23, 0.09, and 0.13, respectively. Estimates of genetic correlations between birth weight and scrotal circumference, volume, concentration, motility, and percents normal, live, and primary and secondary abnormalities were 0.36, 0.07, 0.58, 0.21, 0.20, 0.34, -0.25, and 0.05, respectively. The moderate estimates of heritability for many of the traits indicate potential for favorable selection response. Positive genetic correlations between birth weight and majority of the traits suggest selection to reduce birth weight may compromise semen traits. However, for most traits the expected correlated responses are small.

Last Modified: 4/16/2014
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