Effects of source and level of dietary energy supplementation on in vitro digestibility and methane production from tall fescue-based diets

Authors: TROTTA, RONALD - University Of Kentucky; Klotz, James; HARMON, DAVID - University Of Kentucky

Submitted to: Animal Feed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2018
Publication Date: 8/1/2018
Citation: Trotta, R.J., Klotz, J.L., Harmon, D.L. 2018. Effects of source and level of dietary energy supplementation on in vitro digestibility and methane production from tall fescue-based diets. Animal Feed Science And Technology. 242:41-47. https://doi.org/10.1016/j.anifeedsci.2018.05.010.
DOI: https://doi.org/10.1016/j.anifeedsci.2018.05.010

Interpretive Summary: Cattle on tall fescue pasture are commonly fed dietary supplements by producers to improve productivity and to dilute the toxicity of the fungally infected grass. There are several different feed supplements and mixtures producers can choose to use. The objective of this study was to compare energy supplements commonly available to U.S. beef producers for their effects on digestibility and fermentation characteristics of a fescue-based diet. Supplements evaluated were corn, soybean hulls, corn gluten feed, 2-way combinations, and the 3-way combination of supplements. Results demonstrated that corn and corn-containing combinations had the greatest digestibility. Corn grain supplementation at low levels has the potential to improve performance in cattle grazing tall fescue. Corn grain supplementation increased digestibility and energetic efficiency of a fescue hay diet more than comparable fibrous and blended energy supplements. Therefore, corn supplementation should be incorporated into diets when economically feasible and at the appropriate supplementation levels to increase performance in cattle grazing tall fescue. These results will directly benefit producers trying to make economic and productivity-based decisions on what supplement to purchase and feed to cattle grazing tall fescue pastures.

Technical Abstract: There is a lack of information about the effect of different sources, levels, and the mixtures of energy supplements commonly fed to cattle grazing tall fescue. Therefore, the objective of this study was to evaluate different common energy sources for beef cattle grazing tall fescue using an in vitro fermentation system. Four ruminally cannulated Holstein steers (571 ± 16.1 kg BW) were fed tall fescue hay and served as donors of rumen contents for an in vitro fermentation experiment. Treatments were fescue hay (CON), soybean hulls (SBH), corn gluten feed (CGF), corn (CORN), or combinations (SBH + CGF, SBH + CORN, CGF + CORN, SBH + CGF + CORN) of these. Flasks were incubated for 48 hours and then assessed for true digestibility, VFA and ammonia concentrations, and total gas and methane production. Supplemental energy sources did not affect total VFA concentration, ammonia concentration, valerate proportion, isobutyrate proportion, isovalerate proportion, or acetate:propionate ratio. True digestibility and digestible energy were generally greater than CON (Table 3; P < 0.001) in all CORN containing treatments. The CORN (P < 0.001) and CGF + CORN (P = 0.023) treatments had a lower acetate proportion than CON. Propionate proportion was reduced by CORN (P < 0.001). Corn grain supplementation increased butyrate proportion in all corn-containing treatments (P < 0.035). All treatments containing energy supplements increased methane production and CH4-E (P < 0.027). The DE loss from CH4-E was increased in CORN, SBH + CGF, SBH + CORN, CGF + CORN, and SBH + CGF + CORN (P < 0.01). Corn grain supplementation at low levels (< 0.25% BW) can improve fescue utilization by increasing digestibility and could improve beef cattle production.