Date of Award
Doctor of Philosophy
The importance of region by sire, herd within region by sire and contemporary group within herd by sire interactions were evaluated for 68,271 birth weight, 247,943 weaning weight and 98,790 postweaning gain records supplied by the American Polled Hereford Association. Variance components for sire, region by sire, herd within region by sire, contemporary group within herd by sire and error were estimated using Henderson Method 3 estimation procedures. Sire by region, herd within region by sire and contemporary group within herd by sire variance estimates divided by the sire variance estimates were .57, .93 and 1.71, respectively, for weaning weight, -1.00, -.14 and 1.29, respectively, for birth weight, and -1.19, .14 and 1.22, respectively, for postweaning gain;The average genetic correlation estimates of weaning weight sire expected differences (EPDs) across regions was .64. This value expresses the correlation among progeny of the same sire after the sire evaluation model had accounted for the contemporary group within herd by sire and herd within region by sire interactions. The average genetic correlation estimates of weaning weight sire EPDs across contemporary groups within herds and across herds within regions were .37 and .27, respectively. The correlation estimates indicated that some rank changes were occurring between sire EPDs in different regions, and substantial rank changes of sire EPDs were occurring across herd and contemporary groups. Heritability of weaning weight was .11 across regions, .17 across herds within region, .28 within herd, and .46 within contemporary group;The average genetic correlation estimates among birth weight sire EPDs across regions were .24 and .35 using two different estimation methods. The average genetic correlation estimates among postweaning gain sire EPDs across regions were .21 and .32 using two different estimation methods. The correlation estimates for birth weight and postweaning gain may not fully reflect the true nature of the correlations due to insufficient number of progreny across regions;In general, contemporary group within herd by sire interaction appeared to be an important source of variation for all the traits and should continue to be included as a random effect in future national sire evaluations for the Polled Hereford breed. The data also indicated that performing sire evaluations across regions for birth weight, weaning weight and postweaning gain, while assuming that region by sire effects are negligible, may lead to severe errors in ranking sires in some regions. Separate sire evaluations for each region would yield sire estimates that better reflect the true future progeny performance of a sire in each region.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Joseph Keith Bertrand
Bertrand, Joseph Keith, "Sire by environment interactions for growth traits in beef cattle " (1983). Retrospective Theses and Dissertations. 8453.