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Composition and Digestibility of Smooth Bromegrass Clones Selected for High and Low IVDMD¹

Improvement of the digestibility of forage grasses through breeding has received considerable attention. The objective of this experiment was to evaluate differences in composition and digestibility among smooth bromegrass (Bromus inermis Leyss.) clones selected for high and low in vitro dry matter disappearance (IVDMD). Thirty-five clones of smooth bromegrass from a nursery (Piano silt loam, Typic Argiudoll) established near Madison were analyzed for IVDMD.

In vitro cell wall disappearance (IVCWD), neutral detergent fiber (NDF), acid detergent fiber (ADF), cellulose, hemicellulose and lignin. The 35 clones consisted of 18 clones selected for high IVDMD and 17 selected for low IVDMD. In vitro dry matter disappearance ranged from 54.9% to 66.5%. High IVDMD clones averaged 63.2% IVDMD compared with 59.6% for low IVDMD clones. Neutral detergent fiber concentration in high IVDMD clones was reduced significantly compared with low IVDMD clones. The potential impact of such a reduction of cell wall concentration on forage intake should be evaluated with livestock.

A high negative correlation r = –0.76 was found between lignin concentration in the cell wall and the rate of IVCWD as measured by ending fermentation after 12 hours. This indicates that lignin concentration in the cell wall influenced initial IVCWD. The percentage of Anal cell wall disappearance after 12 hours of incubation in an in vitro system ranged from 22.4% (6.3% lignin in the cell wall) to 41.6% (3.7% lignin in the cell wall). The possible influence of the rate of cell wall disappearance on forage consumption of smooth bromegrass should be studied.

Lignin concentration in the cell wall component was found to be poorly correlated with the extent of IVCWD after 48 hours. No difference existed in the mean IVCWD (48-hr) of high and low IVDMD clones even though high IVDMD clones had a lower lignin concentration in the cell wall (4.1%) compared with low IVDMD clones (5.4%).

Key Words: Cell wall concentration • In vitro dry matter disappearance • In vitro cell wall disappearance • Lignin • Intake • Bromus inermis Leyss. • Acid detergent fiber • Neutral detergent fiber

² Assistant professor and professor of Agronomy, respectively.