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The effect of rumen degradable and rumen un-degradable intake protein on feedlot performance and carcass merit in heavy-yearling steers

J. J. Wagner^*, T. E. Engle and T. C. Bryant

^* Southeast Colorado Research Center, Colorado State University, Lamar, CO 81052 , Department of Animal Sciences, Colorado State University, Fort Collins, CO 80523 JBS Five Rivers Cattle Feeding, Greeley, CO 80634

john.wagner{at}colostate.edu

Abstract

Four hundred and thirty-two crossbred yearling steers (395 kg ± 6.35) were utilized in a randomized block experiment to study the effects of rumen degradable intake protein (DIP) and rumen un-degradable intake protein (UIP) concentration on feedlot performance and carcass merit. Six dietary treatments utilized for this study included: a 10.5% CP diet with 5.1% UIP and 5.4% DIP (DIP5); an 11.5% CP diet with 5.1% UIP and 6.4% DIP (DIP6); a 12.5% CP diet with 5.1% UIP and 7.4% DIP (DIP7); a 13.5% CP diet with 5.1% UIP and 8.4% DIP (DIP8); a 14.5% CP diet with 5.1% UIP and 9.4% DIP (DIP9); and a 14.5% CP diet with 6.1% UIP and 8.4% DIP with the additional UIP provided by corn gluten meal (CGM). There was a linear increase in final BW and ADG and a trend for a linear increase in DMI associated with increasing DIP concentration within the 5.1% UIP treatments. Feed efficiency and net energy recovered from the diet were not influenced by dietary DIP concentration. As diet DIP concentration increased, carcass fat depth and average yield grade (YG) increased linearly and the percentage YG 1 and 2 carcasses decreased linearly. Diet UIP treatment had no effect on final BW, ADG, DMI, G:F, and calculated net energy recovery. For the 14.5% CP diets, marbling score tended to be reduced for steers fed 6.1% UIP as compared with 5.1% UIP. Remaining carcass traits were not impacted by dietary UIP. The results of this study show that the DIP requirement in the finishing diet for heavy yearling steers fed steam-flaked corn is greater than 7.4% of diet DM but likely not more than 8.4% of diet DM when diet UIP is approximately 5.1% of diet DM. Increasing UIP above 5.1% of diet DM did not improve feedlot performance or HCW. Expressed on a CP basis, it appears as if the requirement for CP for heavy yearling steers fed steam-flaked corn based finishing diets is 13.5% of DM with approximately 62% of CP from DIP.

Key Words: crude protein • degradable intake protein • feedlot performance • un-degradable intake protein • yearling steers