Evaluation of Cool Season Grass Species and Varieties Using In Vivo and In Vitro Techniques

Digestibility of the cool season grass species, smooth bromegrass (Bromus inermis Leyss), intermediate wheatgrass [Agropyron intermedium (Host) Beauv.] and the crested wheatgrass complex [Agropyron sibericum (Willd.) Beauv. and Agropyron desertorum (Fisch.) Shult.] was measured at heading and 2 weeks after by in vivo and in vitro techniques. In addition, plant fraction percentages and digestibilities were determined throughout the season for two varieties within each of the above species, ‘Manchar’ and ‘Sac’ bromegrass, ‘Greenar’ and ‘Oahe’ intermediate wheatgrass, and ‘P-27’ Siberian wheatgrass and ‘Nordan’ crested wheatgrass. Both in vivo and in vitro criteria, as well as chemical analyses, indicated that intermediate wheatgrass was lower in digestibility than the other two species. Bromegrass and crested wheatgrass differed very little; bromegrass was slightly superior under in vivo test, while crested wheatgrass was slightly but significantly superior when in vitro techniques were used. A high correlation (r=0.89) was found between in vitro and in vivo dry matter digestibility. At heading and 2 weeks after, in vitro dry matter digestibility indicated that Greenar was significantly superior to Oahe. No significant difference was found between the varieties of the other species. When entire plant and plant fractions were sampled over the growing season, Sac bromegrass was significantly superior to Manchar, Greenar intermediate wheatgrass to Oahe and Nordan crested wheatgrass to Siberian. These results indicate the possibility of selecting for more highly digestible stems and sheaths to produce a variety for utilization at the time of maximumd ry matter yield. For grazing purposes, however, selection at an early stage for whole plant digestibility would seem desirable.