Document Type

Thesis - University Access Only

Award Date

2002

Degree Name

Doctor of Philosophy (PhD)

Department / School

Animal Science

Abstract

Progeny from Charolais sires and Angus-crossbred cows were used to determine genetic mechanisms for differences in postmortem muscle metabolism that influence beef tenderness. Sires were identified in an earlier study as producing progeny with palecolored lean and tender meat (Tender sire group; n = one sire; n = eight progeny) or darker-colored lean and tough meat (Tough sire group; n = two sires; n = 10 progeny). Live animal measurements included chute scores, hormone levels, serum chemistry profiles, and live weight; at harvest, hormone levels and serum chemistry profiles were determined. Temperature, pH, and colorimeter values were determined for longissimus (LD), psoas major (PM), semimembranosus (SM), semitendinosus (ST), and triceps brachii (TB) muscles. Fiber typing and SDSPAGE were conducted on LD muscles and selected muscles were sampled for glycolytic potential, purge loss, and sarcomere length determination. Sensory evaluation was performed on LD and SM at 7 and 14 d postmortem and shear force and cooking loss were measured on_ all muscles examined at various postmortem times. The tender sire group had lower (P < 0.10) cortisol, creatinine phosphokinase, globulin, and total protein levels and higher (P < 0.10) phosphorus than the tough sire group. Carcasses from the tender sire group had lower (P < 0.10) pH at six h postmortem in the LD and ST and lower (P < 0.10) pH at three h postmortem in the SM. Tender sire group carcasses had higher glycolytic potential, longer sarcomeres, and redder and more yellow SM and TB muscles and lighter SM muscles than the tough sire group (P < 0.10). A greater (P < 0.10) amount of 30 kDa region breakdown product was present for the tender sire group at all times postmortem. Steaks from the tender sire group received more desirable (P < 0.10) tenderness scores and lower (P < 0.10) shear force values for LD at 2, 3, 4, 5, 6, 7, 14, 21, and 35 d postmortem, for SM at 4 d postmortem, and for ST at 2, 7, and 14 d postmortem than steaks from the tough sire group. All other measures were similar (P > 0.10) between tough and tender sire groups. Our data suggest that a genetic condition exists in cattle that is characterized by a lessened physiological response to stress resulting in higher postmortem muscle glycogen content and faster pH decline, which leads to longer sarcomeres and enhanced proteolysis causing meat to be more tender. These results could lead to genetic selection for improved tenderness.

Library of Congress Subject Headings

Beef -- Quality Beef cattle -- Genetics Muscles -- Metabolism

Format

application/pdf

Number of Pages

153

Publisher

South Dakota State University

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