Digestion of Alfalfa Hay Observed by Scanning Electron Microscopy

Abstract

A scanning electron microscope was used to observe air-dried Medicago sativa (mature) leaves and stems before and after suspension in nylon bags in ruminally fistulated steers. Initial digestion began with random hydrolysis on the adaxial leaf surface. Leaf cuticle and epidermis were sloughed after 24 hr allowing massive digestion of the mesophyll; only unhydrolyzed cuticle, abaxial hair, and partially hydrolyzed vascular tissue remained. The external surface of alfalfa stem was randomly attacked by sloughing of cuticle and epidermis to expose a dense matrix (cortex) that was partially hydrolyzed during 24 hr in the rumen. Fiber cells were exposed after 48 hr; after 72 hr there was only vascular tissue in the rumen and feces.