Master of Science (MS)
School of Animal Science
The first objective of the current study was to evaluate genetic trends from 10 years of the American Brahman Breeders Association Carcass Evaluation Program from 2004 to 2013. Changes of performance in growth, carcass composition, and carcass quality traits were evaluated. Overall means were calculated to report the total average for each trait along with an average rate of change per year. Growth traits evaluated included feedlot entrance weight (INWT), harvest weight (HRVWT), and average daily gain (ADG). Carcass composition and quality traits evaluated included hot carcass weight (HCW), rib eye area (REA), marbling score (MARB), dressing percent (DP), quality grade (QG), yield grade (YG), and Warner-Bratzler shear force score (WBS). Trends indicated that over the 10 year period of improved sire selection, Brahman cattle began entering the feedlot lighter, exited heavier, and improved average daily gain. Furthermore, all carcass composition and quality traits showed overall improvement with the exception of shear force scores. Further investigation of shear force score showed WBS had in fact been experiencing a favorable downward trend since 2009. The second objective of this study was to evaluate SNP located on six candidate genes and their potential association with growth, carcass composition, and carcass quality traits in a population of Brahman and Brahman-influenced steers that participated in the ABBA carcass evaluation program. Traits analyzed included birth weight (BW), weaning weight (WW), hip height (HH), days on feed (DOF), and the previously mentioned feedlot and carcass traits INWT, HRVWT, ADG, HCW, REA, MARB, DP, QG, YG, and WBS. Single nucleotide polymorphisms (SNP) were chosen for analysis within six candidate genes including Thyroglobulin (TG, Adiponectin (ADIPOQ), Calpastatin (CAST), Calpain-3 (CAPN3), Insulin like growth factor-1 (IGF1), and Growth Hormone gene (GH1). Analysis revealed representation of all six candidate genes in the 41 SNP found to have 58 significant associations (p<.05) with growth and feedlot traits BW, WW, HH, INWT, HRVWT, DOF, and ADG. Furthermore, all six candidate genes were represented in the 32 SNP found to have 49 significant associations with carcass composition and quality traits HCW, REA, YG, MARB, QG, and WBS. No markers showed association with DP.
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Royer, Amanda M., "A Study Evaluating Genetic Trends and Molecular Predisposition to Improved Carcass Quality of Brahman and Brahman Influenced Cattle" (2015). LSU Master's Theses. 3799.