Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2003
Publication Date: 6/15/2004
Citation: Eun, J.S., Fellner, V., Burns, J.C., Gumpertz, M.L. 2004. Fermentation of eastern gamagrass (tripsacum dactyloides [l.] l.) by mixed cultures of ruminal microorganisms with or without supplemental corn. Journal of Animal Science 82:170-178. Interpretive Summary: Silage typically contains large amounts of soluble protein but mainly structural carbohydrates that ferment slowly. This miss match between rate at which energy and N are supplied to microbes increases the loss of N in the rumen. Supplementing with starch often increases microbial protein synthesis. In lactation studies, gamagrass, a perennial native warm-season grass has shown potential as a feed for dairy cattle. Gamagrass has a high concentration of cell walls (600 to 750 g kg-1) but the cell walls have been found to be extensively degraded in the rumen. Furthermore, the cell walls contain 51 to 64% of the N. In this study eastern gamagrass harvested as silage or as hay showed no affect on fermentation by mixed cultures of ruminal organisms. When corn as a source of energy was added to the silage, pH of the cultures were lowered, but had no effect on fiber digestibility. Further, increasing corn to greater than 50% of the diet dry matter increased daily outflow of microbial nitrogen. The extensively degradable cell walls (fiber) and concurrent release of N with corn supplementation (synchronizing N and energy) makes gamagrass a potential base perennial forage for the dairy enterprise.
Technical Abstract: Five dual-flow fermentors (700 mL) were used to determine the effects of eastern gamagrass (Tripsacum dactyloides [L.] L.) diets on microbial metabolism by mixed rumen cultures. Fermentors were incubated with filtered ruminal contents and allowed to adapt for 4 d to diets followed by 3 d of sample collection. Five dietary treatments were tested: gamagrass hay (GH) + no corn (GHNC), gamagrass silage (GS) + no corn (GSNC), GS + low corn (GSLC), GS + medium corn (GSMC), and GS + high corn (GSHC). The experiment was conducted as a randomized complete block design with five treatments and three replications. Total VFA concentrations were not affected by diets. Corn addition linearly decreased molar proportion of acetate (P < 0.001). In contrast, molar proportion of propionate was reduced in GSLC (cubic effect, P < 0.001) and remained similar across all other diets. Corn supplementation linearly increased molar proportion of butyrate (P < 0.001). The acetate + butyrate to propionate ratio was highest in cultures offered GSLC (cubic effect, P < 0.001) and remained similar across all other diets. Feeding GSNC resulted in a higher ruminal pH compared to GHNC (P < 0.03). Increasing the level of corn supplementation in GS linearly decreased culture pH (P < 0.001). All diets resulted in similar methane production with the exception of GSMC which lowered methane output (quadratic effect, P < 0.004). Total substrate fermented to volatile fatty acids and gas tended to be greater with GHNC than GSNC (P < 0.06) and linearly increased with the addition of corn (P < 0.004). Neutral detergent fiber digestibility was similar between GH and GS and was not affected by supplemental corn. Microbial N flow increased in cultures offered GSHC (quadratic effect, P < 0.02). Corn supplementation at the medium and high level linearly decreased C18:0 (P < 0.02) and increased trans-C18:1 (P < 0.004). Including corn at the high level with GS did not have a detrimental effect on ruminal fermentation.