Influence of lignin and silicon on a summative system for assessing the organic matter digestibility of Panicum

Abstract

The effect of lignin and silicon on the digestibility of the neutral detergent solubles (NDS), hemicellulose, cellulose, and organic matter was studied with use of 57 cuts of three cultivars of Particum coloratuni and three of Panicum maximum with known in vivo digestibilities. Lignin had only a small effect on the digestibility of NDS (r = -0.34, P < 0.05) and silicon no effect (r = +0.12, P > 0.05). The main factor controlling the quantity of digestible NDS was the percentage of NDS in the grass (r = 0.98, P < 0.001). The digestibility of both hemicellulose and cellulose was related to the lignification percentage (r = -0.88, P < 0.001). Silicondid not depress the digestibility of hemicellulose + cellulose (r = +0.29, P < 0.05). Lignin had a mean digestibility of 5.5 %. Organic matter digestibility was estimated with a residual standard deviation of ¦ 2.2 digestibility units by summation of individual estimates of digestible NDS, hemicellulose, cellulose, and lignin. The residual variation was not related to the level of silicon (r = 0 .00). It was concluded that the main factors controlling organic matter digestibility were the percentages of both hemicellulose and cellulose present and the extent to which they were lignified. Silicon was not a factor controlling the digestibility of the structural carbohydrate fractions.