Cell walls digestion of ryegrass and lucerne by cattle

In order to learn more about the extent to which the walls of different cell types are digested in vivo. lucerne (Medicago sativa) and Italian ryegrass (Lolium multiflorum) were fed to cattle. The animals were two 9-month old Limousin. Holstein/ Friesian heifers of 180kg live weight were led from each of the 6 replicated plots for 3 days per replicate plot, following an introductory period of 2 days. The feed samples were partially dried in field and then in an oven at 85 degree C for 48 h for animal feeding. The same heifers were subsequently fed dried Italian ryegrass (Lolium multiflorum), following the same procedure as adopted for lucerne feeding. Intake and digestibility of DM and neutral detergent fibre (NDF) and the output of NDF in the faeces for both lucerne and Italian ryegrass were recorded. For microscopic studies a cm length of each plant part was cut from mid portion with razor blade and transferred immediately to formalin acetic acid solution (FAA). The diet and faeces were examined for cell types and wall thickness. The intake of cell wall, estimated as neutral detergent fibre (NDF) was lower in lucerne (2254) than ryegrass (2534), but the reverse was the case for NDF output in faeces. NDF digestibility was much lower (22 units weight) in lucerne than ryegrass. The proportion of plant tissue volume occupied by thick-walled cells was much higher in faeces (69.8%) than in the forage (22.0%) and the proportions of thin- walled (27.1%) and epidermal cells (3.0%) were much lower in Nieces than in the forage (64.5% and 13.5% respectively). A significant proportion of the thin-walled cells partially or entirely escaped from digestion, particularly in ryegrass, suggesting that some plant particles passed out of the rumen very quickly, before there was enough time for even thin walls to be full, degraded. The cell walls measured in the faeces samples were typically thinner than equivalent cell walls in the forage, indicating some degradation in their respective cell walls. The proportion of epidermal cells identified in the faeces undigested particles was low. The position of the epidermal cells on the outside of the plant particles presumably increases their accessibility to rumen microorganisms and so increases the likelihood that their walls will be at least partially degraded. The presence of thin-walled cells in the faeces, especially in the case of ryegrass, appears to be associated with an early escape of particles from the rumen.