Characteristics of Bovine Longissimus and Semitendinosus Muscles from Grass and Grain-Fed Animals

Fifty-four Hereford steers and heifers, equally divided into three groups, were grazed on fescue grass for 180 days. One group was slaughtered after the grazing period and the two remaining groups were fed a high concentrate diet for 56 and 112 days. Longissimus and semitendinosus muscle characteristics of these animals were determined. Carcass quality grades improved with grain feeding. Sarcomeres were longer and fiber diameters were generally less for semitendinosus than for longissimus muscles. Percent moisture declined and ether extractable constituents increased in both muscles as period of grain feeding was increased. Percent protein did not change with grain feeding but was higher for longissimus than for semitendinosus. Collagen content did not change in semitendinosus but declined in longissimus as determined from histological sections. Amount of reticulin did not differ among muscles or due to feeding treatment. Elastin was greater in semitendinosus than in longissimus. Tenderness of both muscles improved with grain feeding but declined for both muscles as internal temperatures were increased from 63 to 68 to 73 C.