The influence of season, chronological age and management on selected forage plant components related to digestibility

Established stands of four warm-season perennial grasses, klein (Panicum coloratum L.), Pretoria-90 (Dicanthium annulatum(Forsak.) Stapf.), Coastal (Cynodon dactylon (L.) Pers.) and Blue buffel (Pennisetum ciliare (L.) Link.) were harvested at two-week intervals for five consecutive harvests within each of three arbitrarily divided growing seasons. The seasons were divided to coincide with spring, summer, and fall growth. Klein and Coastal were sampled prior to frost and at monthly intervals during the dormant season and leaf-stem separations were made on klein. All samples were fractionated into cellular contents (NDE) and cell wall contents (NDF). The neutraldetergent insoluble fraction was partitioned, on a solubility basis, into hemicellulose, cellulose, lignin, and ash. Various chemical components were correlated within vitro digestibility. Percent NDF and NDF constituents varied significantly between species. Seasonal changes in percent NDF with increasing chronological age were dissimilar between species. The NDF content of klein and Costal was higher in hemicellulose and lower in cellulose than that of Pretoria-90 and buffel during each season. Klein showed a more rapid increase in NDF content immediately after frost than Coastal, but by the end of the dormant season there was no significant difference between the two species. The leaves of klein were higher in hemicellulose and ash and lower in cellulose and lignin than the stem fraction. In vitro dry matter digestibility differed significantly between species at the same chronological age. Summer growth was lower in in vitro dry matter digestibility for all species than spring or fall growth. During the dormant season klein was significantly higher in in vitro dry matter digestibility and in vitro cell wall digestibility than Coastal. Klein leaves were significantly higher in IVDDM than stems at each date. Simple regression analyses revealed inconsistent relationship between NDF and components of NDF with IVDDM by seasons. These studies did not reveal any physical or chemical component of warm-season grasses which would adequately estimate in vitro digestibility across species and seasons. Therefore, for the initial evaluation of plant breeding material or samples generated from management studies an in vitro system is suggested