EFFECT OF PHENOTYPIC-EXPRESSION OF BRAHMAN BREEDING ON MARBLING AND TENDERNESS TRAITS

Steers with known proportions of Brahman and Hereford breeding (80 qua rter-bloods, 25% Brahman x 75% Hereford and 79 half-bloods, 50% Brahma n x 50% Hereford) were used to determine the effect of phenotype on ma rbling and beef tenderness characteristics. Three experienced evaluato rs independently classified each live steer according to estimated pro portion of Brahman breeding based on phenotypic evidence of Brahman br eed characteristics. The steers were slaughtered, their carcasses were graded, and a measurement of hump height was obtained for each carcas s. Samples of longissimus muscle were obtained for measurement of 24-h calpastatin activity, sensory panel evaluation, and Warner-Bratzler s hear (WBS) force measurements. Paired steaks were aged (6 and 18 d pos tmortem) and palatability determinations were completed. Estimates of live animal phenotype ranged from 0/16 to 9/16 for quarter-blood Brahm an steers and from 1/4 to 13/16 for half-blood Brahman steers. Neither live animal phenotype nor carcass hump height was correlated with mar bling score. Live animal phenotype was correlated (P < .01) with taste panel tenderness ratings (r(d6) = -.36; r(d18) = -.36) and shear forc e values (r(d6) = .36; r(d18) = .30) Moreover, carcass hump height exh ibited low, negative correlations (P < .05) with panel tenderness scor es (r(d6) = .16; r(d18) = -.28) and low, positive correlations (P < .1 0) with shear force (r(d6) = .13; r(d18) = .16) Steaks from steers cla ssified as more than 3/8 Brahman were tougher (P < .05) than steaks fr om steers classified as 3/8 or less Brahman. Steaks from carcasses wit h hump height measurements of 7.60 cm or greater had lower panel tende rness ratings and higher WBS values (P < .05) than steaks from carcass es with hump heights less than 6.35 cm. Quarter-blood and half-blood B rahman steers that were similar in phenotype produced steaks that were similar in tenderness. Results of this study suggest that as phenotyp ic evidence of Brahman breeding increases the tenderness of cooked ste aks from Brahman crossbred steers decreases.