|Mitchell, Robert - Rob|
Submitted to: Midwestern Section of the American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 10/19/2007
Publication Date: 3/17/2008
Citation: Schwarz, A.K., Godsey, C.M., Luebbe, M.K., Erickson, G.E., Klopfenstein, T.J., Mitchell, R., Pedersen, J.F. 2008. Forage quality and grazing performance of beef cattle grazing brown mid-rib grain sorghum residue. American Society of Animal Science Midwest Section/American Dairy Science Association Midwest Branch Abstract 288 pg. 92, March 17-19, 2008, Des Moines, IA.
Technical Abstract: Residue from grain sorghum hybrids, one control (AWheatland x RTx430) and its near isogenic with the brown mid-rib (BMR) trait, were compared in a 72-d grazing experiment. Forty eight steers (250 ± 23 kg) were stratified by BW and assigned randomly to 2.12 ha paddocks (6 steers/paddock) containing BMR or CON grain sorghum residue. Steers grazed from November 27, 2006 to February 7, 2007. Metal ex-closures were placed in each paddock and sampled to compare residue quality when not grazed. Residue was sampled on day 4, 30, and 60 of the grazing period by collecting all residue from a 92-cm row in each paddock. Samples were separated into leaf and stem fractions, and analyzed for NDF and in-vitro NDF digestibility (IVNDFD). Steers grazing BMR (0.56 kg/d) residue gained more (P<0.01) than CON (0.34 kg/d) and had greater ending BW (P>0.01). No difference in NDF content of the leaf fraction was observed between CON and BMR across date (P=0.41), averaging 67.6% for BMR and 66.9% for CON. Leaves had greater (P<0.01) IVNDFD in BMR than CON with an increase of 6-12% units. A 13-19% unit increase for IVNDFD was observed for BMR compared to CON (P<0.01) in the stem fraction, however, the stem fraction is likely not consumed to the extent of the leaf fraction. IVNDFD decreased over time in the leaf fraction, regardless of treatment, with an 8-12% unit decrease in the grazed areas over the entire grazing period, and a 2-4% unit decrease over time in IVNDFD for the non-grazed ex-closures. An interesting observation was that although there appeared to be a significant difference (P<0.01) in IVNDFD between the leaf and stem fractions of the CON treatment, IVNDFD was comparable between the leaf and stem fractions in the BMR hybrid (P>0.05). This suggests cattle could consume the stem residue of the bmr-grain sorghum hybrid and perform similar to grazing the leaf fractions, if stems are palatable. Incorporation of the BMR trait increases gain, by increasing fiber digestibility. Key Words: Beef cattle, (Brown mid-rib), Crop residue, (Grain sorghum) [note: only one or the other in parentheses]