Abstract
Effects of ingestive mastication on physical degradation of Coastal bermudagrass hay (CBH), grazed Coastal bermudagrass (GCB) and grazed ryegrass (GRG) were studied macro-scopically, microscopically and histochemically. The masticate of each forage was collected from cattle fitted with 5-cm id esophageal cannulae and separated into fragments retained on sieves of 20 to 1,600-µm. Masticated particles passing a l,000-µm sieve made up 15.5, 51.9 and 25.8% (by weight) of the consumed CBH, GCB and GRG, respectively. Particles retained on sieves of 500, 800, 1,000 and 1,600 µm appeared as irregular sized particles of leaf and stem characterized by ends formed from totally crushed vascular bundles (VB) and edges defined by cleavage between VB. The central areas of these fragments contained many sites of rupture of the cuticle, partial fracturing of the VB and exposure of the epidermis and mesophyll. Observed only in GRG were large isolated sheets of cuticle with attached and readily exposed mesophyll or epidermal cells. Particles of 100 to 500 µm appeared to be derived largely by further reduction in VB length and longitudinal fracturing between the VB. Particles <100 µm (<10% of the masticate) were represented by epidermis, cuticle, layers of parenchyma bundle sheath cells and isolated VB. Based on their anatomy and histochemistry, they appeared higher in indigestible tissue (lignin staining) components than most larger particles. Mastication decreased particle size and thereby exposed more surface area. Additionally, the crimping and crushing action of the mastication process exposed more area of digestible tissue within a given particle size. In view of the protective nature of intact plant structures, ingestive mastication appears important in disrupting these anatomical barriers to subsequently allow increased microbial enzyme accessibility. Copyright © 1984. American Society of Animal Science . Copyright 1984 by American Society of Animal Science.