Variation in Forage Component Composition and In Vitro Digestion of Creeping Bluestem
Creeping bluestem [Schizachyrium scoparium (Michx.) Nash var. polycladus (Scribner & Ball) Bruner (S. stoloniferum Nash)] is predominant, high yielding range grass native to Florida; however, in vitro organic matter digestion (IVOMD) is low. This research investigated IVOMD variation in 200 creeping bluestem ecotypes grown on an area of Onka Fine Sandy (sandy, siliceous, Hyperthermic Typic) and Myaxxa Fine Sand (sandy, siliceous, hyperthermic Arenic Haplaquod) soils. Ecotypes were collected from peninsular Florida, and space planted in a nursery. Plants were staged to 150 mm stubble in March 1984 and 1985 and the forage discarded. In late June of each year while plants were vegetative, leaves from each ecotype were hand harvested (150 mm stubble), and analyzed for IVOMD, which ranged from 350 to 642 g kg−1. (P < 0.001). Fifteen ecotypes with four replications in each of 2 yr (120 samples), representing the range in IVOMD, were selected to determine relationships between IVOMD and both concentration and in vitro digestion of fibrous components. A linear relationship (P < 0.05) existed between IVOMD and acid detergent lignin (ADL; r −0.66) concentration. A quadratic relationship (P < 0.05; r = 0.66) was found between IVOMD and in vitro hemicellulose (HC) digestion, indicating that HC was not the major structural component limiting IVOMD of creeping bluestem. In vitro rate of neutral detergent fiber (NDF) digestion was not related to IVOMD (P > 0.05; r = 0.14); however, lag time was shortest (P < 0.05; r = −0.74) ecotypes highest in IVOMD. Regression coefficients for relationships between in vitro digestion of OM, NDF, acid detergent fiber, and HC vs. ADL concentration were negative and significant for the linear contrast. In vitro lag time was highest for ecotypes highest in ADL. In conclusion, variation exists in IVOMD of creeping bluestem ecotypes found in Florida, and appears to be due primarily to the inhibitory effects of lignin on the initiation and extent of forage digestion.
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