Digestion of Corn and Sorghum Silage Observed by Scanning Electron Microscopy2

Scanning electron microscopy was used to observe the effects of ensiling and ruminal degradation on leaves and stems of corn and sorghum. Bacteria were more active on adaxial than abaxial leaf surfaces of both corn and sorghum during ensiling. Hydrolytic activity occurred in starch granules of corn silage that accumulated along vascular protrusions of adaxial leaf surfaces. Hydrolysis of starch was evident on each species of ensiled stem tissue, but no degradation of parenchymal cells or vascular tissue was observed. Rumen microorganisms preferentially digested leaf mesophyll and stem parenchyma in both silages. Mesophyll from leaves disappeared by 24 hours. Microbes apparently gained access to corn silage leaves more readily than sorghum leaves because the adaxial epidermis of corn leaves loosened and broke more readily. Only the lignified tissues remained after 48 hr digestion. The lignified tissues included leaf epidermis and vascular tissue from leaves of both silages and vascular tissue from corn stems. A portion of sorghum silage stem parenchyma remained after 72 hours. Qualitative energy dispersive X-ray analyses indicate silicon is localized in adaxial and abaxial cells of corn and sorghum leaf epidermis. Relatively higher concentrations of silicon were located over veins with lesser amounts in adjacent tissues. Silicon is deposited in stem epidermal tissue. Dispersion of silicon in internal structures of leaf and stem tissues was too low to differentiate from Bremsstrahlung. Silica appears to inhibit digestion through epidermal tissues.