Nutritive Quality of Four Perennial Grasses as Affected by Species, Cultivar, Maturity, and Plant Tissue

Improved perennial grasses provide ranchers with high-quality forage for grazing and hay. However, in the Northern Great Plains of the USA, nutritive quality information is limited on both established and new cultivars. This study compares the nutritive quality of established and more recently released cultivars of crested wheatgrass [Agropyron desertorum (Fisch. ex Link) Schultes] (CWG), intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth and Dewey] (IWG), western wheatgrass [Pascopyrum smithii (Rydb.) Love] (WWG), and smooth bromegrass (Bromus inermis Leyss.) (SBG); evaluates the effect of plant maturity on tissue quality; compares nutritive quality differences among species; and evaluates nutritive quality relationships. Smooth bromegrass leaf tissue had the highest (P < 0.05) in vitro dry matter digestibility (IVDMD) and lowest neutral detergent fiber (NDF), but IWG and WWG had higher stem IVDMD. Few quality differences were detected between cultivars within a species, but 'Rosana' WWG had higher (P < 0.10) stem and whole plant IVDMD than the more recently released 'Rodan'. Leaf percentage differed significantly (P < 0.05) among species, with WWG (49.8%) having the highest, and CWG (21.2%) the lowest. Correlation coefficients between quality measurements suggest that if grass leaf tissue were selected for higher IVDMD, leaves should also have higher crude protein (CP) and lower NDF. This relationship was best illustrated with WWG for all three tissue types. The apparent lower quality of Rodan WWG compared with the older cultivar, Rosana, should caution plant breeders to monitor forage quality to ensure that selection for improved agronomic traits does not compromise nutritive quality.