The rate and extent of cell-wall degradation in vitro for 40 silages varying in composition and digestibility

Abstract

The rate and extent of cell-wall degradation was recorded in 40 silages in order to explore the variation between silages and provide material and results to use in the search for a lower cost method. The method used in the present study was selected from four compared previously (Wilman et al., 1996. Anim. Feed Sci. Technol., 63, 99–109). Freeze-dried, milled silage was incubated in buffered rumen fluid in sealed tubes for 0, 3, 8, 16, 24, 45 or 72 h and then boiled with neutral detergent. The constants a, b and c in the equation p = a + b(1 − e − ct ) (Ørskov and McDonald, 1979. J. Agric. Sci. Cambridge, 92: 499–503.) (where p is the percentage of cell wall degraded after t hours of incubation) were calculated for each silage. The rate of cell-wall degradation in the early stages of fermentation was much higher in a lucerne silage than in the grass and forage maize silages. Mixtures of lucerne and forage maize were intermediate in rate of cell-wall degradation. Among 28 grass silages, ‘ c’ varied from 0.029 to 0.066, indicating wide variation in rate of cell-wall degradation; ‘ c’ was negatively correlated with the cell-wall content of the silage ( r = − 0.81), suggesting that the cell wall from the younger, leafier crops was degraded more quickly than that from more mature crops. The cell-wall degradation curve from 3 to 72 h of incubation was well described by the equation p = ( a + b)(1 − e − c( t − t o ) ), where t o is the lage period before rapid degradation began. In the case of the 28 grass silages there were strong correlations between ‘( a + b)’ and cell-wall degradation after 72 h ( r = +0.92) and between ‘ c’ and cell-wall degradation after 24 h as a percentage of cell-wall degradation after 72 h ( r = +0.95), suggesting that, for some purposes, it may be sufficient to have only 0, 24 and 72 h of incubation.