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Forage Quality Evaluation of Two Warm−Season Range Grasses Using Laboratory and Animal Measurements

Griffin, J. L., Wangness, P. J., Jung, G. A.
Agronomy journal 1980 v.72 no.6 pp. 951-956
Andropogon gerardii, Festuca arundinacea, Panicum virgatum, animal feeding, autumn, beef, beef cows, cool season grasses, developmental stages, digestible dry matter, dry matter intake, forage grasses, forage quality, grass hay, herds, in vitro digestibility, nutrient requirements, protein supplements, regrowth, spring, summer, warm season, warm season grasses, wethers, Pennsylvania
The shortage of available forage during mid−summer is considered a major factor limiting the size of beef cowcalf herds in the Northeast. Consequently, using warmseason perennial range grasses as a supplement to existing cool−season grass forage programs is being considered. Animal feeding trials were conducted to assess the forage quality of ‘NY 1145’ big bluestem (Andropogon gerardi Vitman), and ‘Blackwell’ switchgrass (Panicum virgatum L.) grown in Pennsylvania. Laboratory and animal estimates of digestibility were compared. Warm−season grass hays harvested at early head emergence, 2 weeks later, and at a regrowth stage in fall were fed with protein supplement to growing wether sheep in the first trial. In vivo digestible dry matter (DDM) of the hays ranged from 67 to 74%. Big bluestem and switchgrass DDM decreased 0.50 and 0.36 percentage units/ day, respectively, when harvest was delayed 2 weeks after head emergence, but dry matter intake (DMI) was not affected. Warm−season grass DDM and DMI were equal or superior to those for summer or fall harvested ‘Ky 31’ tall fescue (Festuca arundinacea Schreb.). In the second trial, DDM of big bluestem and switchgrass hays harvested at early head emergence and fed to mature wether sheep without protein supplement ranged from 56 to 69%. Digestible dry matter and DMI for the warm−season grasses were generally lower than those for tall fescue harvested in spring at the same growth stage. In both animal studies, rankings of the grass hays using in vitro dry matter digestibility (IVDMD) and DDM estimates did not differ. The IVDMD technique did underestimate DDM by approximately 17 percentage units. This emphasizes the importance of animal evaluation in supporting laboratory forage quality analyses. Results suggest that big bluestem and switchgrass forage, harvested at early head emergence or later, appear most suitable for animals with lower nutrient requirements, such as beef cows.