Disparity of dietary effects on collagen characteristics and toughness between two beef muscles.

Manipulation of growth rate and/or diet has been shown to affect protein turnover and may be used to improve beef quality. This trial was conducted to evaluate the effects of average daily gain (ADG) and diet on animal performance, collagen characteristics and beef quality of two different muscles; longissimus dorsi (LD) and semitendinosus (ST). Seventy six Hereford and Angus steers were assigned to three dietary management regimens for finishing: high grain diet based on corn (n=28), alfalfa pasture (n=22) and grass pasture (n=26). Average daily gains were greater (P<0.001) in Herefords vs. Angus and for corn- vs. pasture finished cattle. Overall, total collagen content was greater (P<0.001) and the percentage of total collagen that was heat soluble was lower (P<0.0001) for ST than for LD muscle. The lowest (P<0.05) values for both total and heat soluble collagens were found in animals finished on corn. WBSF values for LD were greater (P<0.01) in grass-fed vs. alfalfa- and grain-finished cattle while there was no difference in WBSF values for ST between grass- and corn-fed animals. No correlation between ADG and WBSF was observed for any muscle. ADG was not correlated with collagen solubility in ST, but was correlated (P<0.05) with collagen solubility in LD. A key finding is that growth rate affected heat soluble collagen in the two muscles to a different extent. In conclusion, this study shows that different feeding strategies may not influence the tenderness of all muscles in a similar way.