Influence of Breed and Diet on Growth, Nutrient Digestibility, Body Composition and Plasma Hormones of Brangus and Angus Steers

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Abstract
Two split-plot designed experiments were conducted to determine the effects of breed (Angus, A, or Brangus, B) and diet (fescue hay, FH; corn silage, CS; or concentrate) on composition and rate of growth, diet digestibility and plasma hormones of steers. In Exp. 1, 10 steers (five of each breed) were fed a CS-based diet followed by a FH-based diet for two consecutive 60-d periods. Both breeds had lower (P < .01) DM intake and digestibility when fed FH than when fed CS diets. The B steers had higher (P < .01) plasma insulin concentrations than A steers when fed the CS diet. In Exp. 2, during two consecutive years, 10 steers previously fed CS- and FH-based diets were finished with a corn silage-whole shelled corn-based diet. During yr 1, A steers had higher (P < .01) DM intake and plasma triiodothyronine (T3) and thyroxine (T4) concentrations (P < .05) than B steers did. Although final weights were similar (P > .10), A steers had heavier (P < .05) carcass weights than B steers did. During yr 2, A steers had higher (P < .07) DM and starch digestibilities and higher (P < .01) plasma T4 concentrations than B steers did. The greater (P < .01) energetic efficiency of A steers was attributed to the greater rates of fat deposition during yr 2. Regardless of type of diet fed, A steers were more efficient at depositing energy. Higher circulating T4 concentrations of A than B steers may explain some of the physiological differences between these breeds.