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

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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. Copyright © 1988. American Society of Animal Science . Copyright 1988 by American Society of Animal Science.

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