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ARS Home » Research » Publications at this Location » Publication #169565
Title: EXAMINING THE GENETIC DIVERSITY OF HEREFORD CATTLE

Author
item Blackburn, Harvey
item CLEVELAND, M. - COLORADO STATE UNIVERSITY
item ENNS, R. - COLORADO STATE UNIVERSITY
item GARRICK, D. - COLORADO STATE UNIVERSITY

Submitted to: Journal of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2004
Publication Date: 7/20/2004
Citation: Blackburn, H.D., Cleveland, M.A., Enns, R.M., Garrick, D.J. 2004. Examining the genetic diversity of hereford cattle. Journal of Animal Science. 82(Suppl 1):451.

Interpretive Summary: The genetic diversity in the U.S. Hereford population was evaluated for level and rate of inbreeding and effective population size. Pedigree records for 20,624,418 animals were obtained from the American Hereford Association. Inbreeding coefficients from animals born in 1900 to 2001 were computed and the annual mean inbreeding coefficients were determined. Inbreeding increased in a linear fashion reaching a maximum of 0.115 in 1966. The rate of inbreeding was not constant over time and five periods were identified in which inbreeding was changing at different linear rates, including a decrease after 1966. Almost 95% of 2001 born individuals were inbred, and the maximum inbreeding coefficient was 0.759. An effective population size of 85 head was calculated. Most of the population is inbred suggesting that inbreeding levels should be factored into future mating programs to minimize the effects of inbreeding depression and the loss of genetic diversity.

Technical Abstract: This study characterized genetic diversity in the U.S. Hereford population by examining the level and rate of inbreeding and effective population size. The impact of breeding structure on inbreeding was evaluated. Pedigree records for 20,624,418 animals were obtained from the American Hereford Association. Inbreeding coefficients for 1900 to 2001 born animals and the mean annual inbreeding coefficients (Fm) were computed from the pedigree. The rate of inbreeding and effective population size were calculated for a subset of the pedigree using all animals born from 1990 to 2001. Inbreeding increased in a linear fashion reaching a maximum Fm of 0.115 in 1966. The rate of inbreeding was not constant over time and five periods were identified in which inbreeding was changing at different linear rates, including a decrease after 1966. Almost 95% of 2001 born individuals were inbred, and the maximum inbreeding coefficient was 0.759. For animals born between 1990 and 2001 inbreeding was less than 0.10 for 56% of the population and ranged from 0.10 to 0.199 for 34% of the population. The mean rate of inbreeding from 1990 to 2001 was estimated as 0.12%, equating to an effective population size of 85 animals. Influential sires and their contribution to the population were identified to help explain changes in the inbreeding trend. A potential explanation for the decrease in inbreeding levels from 1967 to 1986 may be a shift in the popularity of within breed lines leading to a decrease in coancestry among influential sires and selected dams. The fluctuation of inbreeding suggests that changing breeding objectives impacted sire selection, but further study of selection decisions contributing to inbreeding in successive generations is needed. Most of the population is inbred suggesting that inbreeding levels should be factored into future mating programs to minimize the effects of inbreeding depression and the loss of genetic diversity. Key Words: Hereford Cattle, Inbreeding, Genetic Diversity