Effects of breed and dietary energy content within breed on growth performance, carcass and chemical composition and beef quality in Hereford and Simmental steers

Forty-eight Hereford and 60 Simmental steers were used to evaluate breed di fferences as affected by dietary energy content on growth performance, carc ass and chemical composition, and beef quality. Diets were based on corn si lage, alfalfa haylage, whole corn, and SBM and were formulated to provide 2 .52 to 2.81 Mcal kg(-1) ME and 11.7 to 12.6% protein in the growing phase a nd 2.69 to 2.86 Meal kg(-1) ME and 9.7 to 10.4% protein in the finishing ph ase. Low- and high-energy diets were formulated for each breed with the hig h-energy diet for Hereford serving as the low-energy diet for Simmental. St eers were slaughtered after attaining 8 to 10 mm backfat determined by ultr asound. Higher energy diets increased (P < 0.09) average daily gain (ADG) a nd feed efficiency within both breeds. Hereford gained more rapidly (P= 0.0 74) and were more (P= 0.001) efficient in converting feed to gain than Simm ental. High-energy diets decreased (P= 0.001) days on feed for both breeds and increased(P= 0.001) carcass weights for Simmental. Otherwise, carcass a nd chemical composition were generally unaffected by dietary energy content . Simmental were heavier (P= 0.001) and leaner (P = 0.001) than Hereford wh ile marbling classification and intramuscular fat content were similar (P > 0.10) between breeds. While shear force decreased(P= 0.043) feeding the lo w-energy diet to Simmental, other shear and palatability attributes were un affected by dietary energy content or breed. Altering dietary energy conten t for Hereford and Simmental influenced growth performance without affectin g carcass and chemical composition and beef quality.