Doctor of Philosophy (PhD)


Animal Science (Animal, Dairy, and Poultry Sciences)

Document Type



Calpastatin activity at 24 h postmortem is inversely proportional to postmortem tenderization and accounts for a greater proportion of the variation in beef tenderness. Tenderness was determined by measurement of 24 h postmortem longissimus muscle calpastatin activity (CA) and Warner-Bratzler shear force after 7 and 14 d of steak aging. The quantitative inheritance of tenderness in Brahman steers was investigated phenotypically by Multiple Trait Derivative-Free Restricted Maximum Likelihood (MTDFREML) procedures and genotypically by using restriction fragment length polymorphisms (RFLP), a microsatellite marker, and DNA sequence analyses. In experiment 1, MTDFREML was used to obtain the genetic parameters of tenderness traits and their genetic and phenotypic correlations with carcass traits such as fat thickness, hot carcass weight, rib eye area, marbling score, and hump height. Contemporary group (CG) was defined as members that were exposed to the same environmental conditions with respect to year of birth and slaughter group. The statistical model included fixed effects of CG, random effects for animal, and residual effects with the covariable of slaughter age. Heritability estimates were 0.44 ± 0.17, 0.30 ± 0.14, and 0.21 ± 0.11 for calpastatin activity, d-7 shear force, and d-14 shear force, respectively. High heritability and additive genetic correlation estimates for CA and shear force indicated that genetic factors made a large contribution to the variation in tenderness and, therefore, tenderness traits would be reliable predictors not only for the rate of tenderization during the beef aging process but also for carcass characteristics. In experiment 2, DNA samples were extracted for RFLP, microsatellite marker, and DNA sequence analyses from the CG of Brahman steers. No DNA polymorphisms were detected in a RFLP procedure conducted for a region between inhibitory domain I and inhibitory domain II of the calpastatin gene. However, microsatellite marker and DNA sequence analyses conducted on the calpastatin promoter region and a region within the L-domain, respectively, revealed distinctive genetic polymorphisms within the calpastatin gene. These findings indicate that the polymorphic sites identified may reveal specific allelic diversity and such alleles may be used as a marker of tenderness for Brahman steer breeding.



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Committee Chair

Donald E. Franke