Use of processing to explore the factors affecting the digestion of forage cell walls

The dried herbage of early and late cut lucerne, red clover, Italian and perennial ryegrasses and timothy was offered in the long form or three processed forms at three levels of feeding (20, 30 and 40 g DM/kg LW) to store lambs in two experiments. Faecal output of organic matter and cell walls was determined.The potential digestibility of the cell walls of these feeds was determined in vitro. The depression in the cell wall digestion from this potential, observed in vivo, was related to water soluble carbohydrate content (WSC) and buffering capacity (BC) of the forages, their fineness of grinding (MF) and the level of feeding (LF).Uniform processing altered the chemical composition of all forages and produced a wide range of MF in the different forages.The digestion of the cell content fraction of the diets was not influenced by herbage species, fineness of grinding or level of feeding.The digestion of organic matter and cell wall was depressed by increasing LF and decreasing MF (P < 0.001) and the interaction between herbage species and processing was significant (P < 0.001).WSC and LF were positively correlated (r = +0.706 and +0.611), and BC and MF were negatively correlated (r = ?0.498 and ?0.498), with the depression observed in cell wall digestion.These four parameters, together with their significant interaction terms (WSC × BC), (WSC × LF) and (BC × MF), accounted for 95.1% of the variance observed in the depression of cell wall digestion and provided a basis for a hypothetical model of factors affecting cell wall digestion.