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Effects of Previous Forage Systems on Feedlot Performance, Body Composition and Plasma Variables of Finishing Steers¹

University of Missouri, Columbia 65211

Abstract

During two consecutive years (Trials 1 and 2), the effects of previous forage system on subsequent feedlot performance, body composition and plasma variables were studied. Fifty-four Hereford yearling steers grazed tall fescue (TF), smooth bromegrass-red clover (BG-RC) or orchardgrass-red clover (OG-RC) pastures before being finished on a high-grain diet. During the first 56 d in the feedlot (Trial 1), live weight and body protein were lower (P < .05) for steers that grazed TF compared with steers that grazed OG-RC, which, in turn, were lower (P < .05) than for the BG-RC treatment. Body fat was lower (P < .05) for steers that grazed TF than for those that grazed BG-RC and OG-RC. Feedlot daily gains, DMI and feed conversions were similar (P > .05) among treatments. No compensation was observed in live weight, body protein or body fat during the first 56 d of finishing. Previous grazing system did not influence (P > .05) plasma glucose and insulin concentrations. During the initial 56 d in the feedlot (Trial 1), steers that had grazed TF had lower plasma urea-N (PUN) concentrations (P < .05) and different linear, quadratic and cubic responses in PUN concentration as days in feedlot increased than steers that had grazed BG-RC and OG-RC. As well, steers that had grazed TF had lower triiodothyronine (T₃) concentrations (P < .05) and tended to have lower thyroxine (T₄) concentrations (P < .10), than steers that had grazed OG-RC. During Trial 2, there were no differences (P > .05) in PUN, T₃ or T₄ concentrations among treatments. Concentrations of PUN were highest (P < .05) directly off pasture in both trials. Plasma glucose, insulin, T₃ and T₄ concentrations increased as dietary energy increased. In conclusion, compensation was not observed in weight, body protein or body fat during the 56-d trial for steers that had previously grazed TF; however, these steers had lower PUN and thyroid hormone concentrations.

¹ Technical article no. 10347 of the Missouri Agric. Exp. Sta.

² Dept. of Anim. Sci., Texas Tech. Univ., Box 4169, Lubbock 79409.

³ Dept. of Animl. Sci., Univ. of Missouri, Columbia 65211.

⁴ Dept. of Food Sci. Nutr., Univ. of Missouri, Columbia 65211.

⁵ Forage Systems Res. Center, Linneus, MO 64653.

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