ARS | Publication request: Unique Dairy Applications for Eastern Gamagrass in Central Wisconsin: II. Nutritive Value and Energy Density

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 4, 2010
Publication Date: October 7, 2010
Citation: Coblentz, W.K., Hoffman, P.C., Jokela, W.E., Bertram, M.G. 2010. Unique Dairy Applications for Eastern Gamagrass in Central Wisconsin: II. Nutritive Value and Energy Density. Agronomy Journal. 102:1720-1730.

Interpretive Summary: Recently, perennial warm-season grasses have received considerable interest, largely as biomass for bioenergy initiatives. But their suitability for limiting caloric intake by fiber-demanding livestock, such as dairy heifers and dry cows, has not been explored. Our objectives were to evaluate eastern gamagrass forages [harvested from one- or two-cut systems with four nitrogen (N) fertilization regimes] for mineral, protein, and fiber composition, and then to estimate the energy densities for these eastern gamagrass forages. By approximately 15 August, eastern gamagrass forages harvested from one-cut systems in central Wisconsin was high in fiber but contained less lignin (a component of fiber) than eastern gamagrass grown at more southerly latitudes. As a result, energy estimates determined by one method (acid-detergent lignin) remained quite high through mid-August, so there would be little potential for the grass to dilute energy with dairy heifer diets. However, when an alternate method was used to estimate energy (neutral detergent fiber digestibility), estimates were much lower for that mid-August harvest date, which would allow some potential for energy dilution within dairy-heifer diets. Unfortunately, the methods used in this study could not confirm or reject whether eastern gamagrass grown in a cool environment is truly low-energy forage; this unresolved issue needs to be clarified through animal feeding studies. However, eastern gamagrass appears to yield high concentrations of fiber when grown in a cool environment, and potential exists to take advantage of these high fiber concentrations by limiting energy intakes by dairy heifers or dry cows on the basis of gut fill. This work is important because it offers potential to limit dry matter and caloric intakes in dairy heifers and thereby avoid overweight conditions.

Technical Abstract: Recently, perennial warm-season grasses have received considerable interest, largely through bioenergy initiatives, but their suitability for limiting caloric intake by fiber demanding livestock, such as dairy heifers and dry cows has not been explored. Our objectives were to evaluate eastern gamagrass [Tripsacum dactyloides (L.) L.] forages harvested from 9 one- or two-cut systems with four N fertilization regimes for macromineral, protein, and fiber composition, and then to estimate the energy densities for these eastern gamagrass forages by the summative approach. Across the 3-yr trial, concentrations of neutral-detergent fiber (NDF) from one-cut systems increased with mostly linear (P < 0.001) and quadratic (P = 0.010) effects of harvest date, reaching maximum concentrations ranging from 746 to 801 g kg-1 by early or mid-August. Similarly, concentrations of lignin increased with delayed harvest dates across one-cut systems in predominantly linear (P < 0.001) patterns. Generally, concentrations of lignin were lower than reported for eastern gamagrass forages grown at more southerly latitudes, and ranged from 37.5 to 46.0 g kg-1 in mid-August. As a result, estimates of total digestible nutrients (TDN) determined by the acid-detergent lignin option for calculating truly digestible fiber remained relatively high through mid-August (582 g kg-1). Adjusting truly digestible fiber on the basis of the alternate NDF digestibility (NDFD) approach resulted in reduced TDN estimates for eastern gamagrass. In northern climates, eastern gamagrass forages have concentrations of NDF, and could be used to dilute dietary energy for livestock species with low or moderate energy requirements.