Location: Wheat, Sorghum and Forage ResearchTitle: Forage Quality and Grazing Performance of Beef Cattle Grazing Brown Mid-rib Grain Sorghum Residue Author
|Mitchell, Robert - Rob|
Submitted to: Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 10/28/2009
Publication Date: 3/15/2010
Citation: Watson, A.K., Geis, J.R., Griffin, W.A., Erickson, G.E., Klopfenstein, T.J., Mitchell, R., Pedersen, J.F. 2010. Forage Quality and Grazing Performance of Beef Cattle Grazing Brown Mid-rib Grain Sorghum Residue. Abstract. Midwest Animal Science Meeting, March 15-17, 2010, Des Mones, IA. Interpretive Summary:
Technical Abstract: Residue from two grain sorghum hybrids, the control AWheatland x RTx430 (CON) and its near-isogenic hybrid containing the brown mid-rib gene bmr12 (BMR), were compared in a 2 year study. Forty-eight steers (236 ± 23 kg) in each year were assigned randomly to 2.12 ha paddocks (6 steers/paddock) containing BMR or CON grain sorghum residue. Steers grazed from early December until early February. Exclosures were placed in each paddock and sampled to compare residue quality when not grazed. Residue was sampled throughout the grazing period. Stem and leaf fractions were analyzed for NDF content and in-vitro NDF digestibility (IVNDFD). Steers grazing BMR gained more (0.63 kg/d; P<0.01) than CON (0.47 kg/d) and had greater ending body weight (P<0.01). There was no interaction between year and treatment (P = 0.20). No difference in NDF content of the leaf fraction was observed between CON and BMR (P = 0.82), averaging 70.7% for BMR and 70.1% for CON. Leaves from BMR paddocks were 6 to 12% units and stems were 13 to 19% units more digestible than CON paddocks (P < 0.01) for IVNDFD. Stems and leaves from BMR paddocks had similar IVNDFD (P > 0.05) while stems were lower in IVNDFD compared to leaves for CON (P < 0.01). This suggests that if stems were palatable, cattle would receive a similar amount of energy from either stems or leaves in BMR grain sorghum residue. Weather conditions and the selective grazing habits of cattle subtly influenced IVNDFD of the residue over time. In year 1, the grazed areas decreased in IVNDFD over time for both BMR and CON paddocks. In year 2 there was a quadratic effect with IVNDFD of BMR and CON being highest in the middle sampling period. In year 1 IVNDFD of grazed areas decreased more rapidly than ungrazed areas and in year 2 there were no differences between grazed and ungrazed areas. Calves grazing BMR grain sorghum residue have increased ADG due to increased fiber digestibility compared to conventional hybrids.