Published online by Cambridge University Press: 27 March 2009
The effectiveness of chewing by sheep during eating in breaking a forage diet into particles was studied in twelve plant species over 2 years and related to the physical structure of the plants and their rate of intake. The twelve species were: Trifolium repens L., Medicago sativa L., Onobrychis viciifolia Scop., Desmodium intortum (Mill.) Urb., Brassica napus L., Spergula arvensis L., Lolium perenne L., Lolium multiflorum Lam., Festuca arundinacea Schreb., Chloris gayana Kunth, Cenchrus ciliaris L. and Zea mays L. In each case early harvesting was compared with later harvesting. The plants were grown in a heated glasshouse.
L. perenne and L. multiflorum were broken into a large number of particles per g dry matter; the particles were rather long and thin. F. arundinacea was broken into heavier, slightly shorter and slightly wider particles. C. gayana and C. ciliaris were broken into particles which were smaller, heavier and contained more vascular bundles than those of Lolium, reflecting the lower rate of intake, greater weight per unit area of leaf blade and greater proximity of bundles of the tropical grasses. Z. mays leaf blades broke into shorter, wider particles than the leaf blades of the other grasses, reflecting the much wider blades of Z. mays.
The leaflets of the four leguminous species and the leaf blades of B. napus were broken into particles with an average length:width ratio of c. 2:1, compared with an average ratio of c. 7:1 for particles derived from grass leaf blades other than those of Z. mays. The legume leaf petioles were broken into particles with an average length: width ratio of c. 13:1; many of the legume petioles were not split longitudinally during chewing. The stems of M. saliva and D. intortum were broken into particles similar in length and width to those from the stems of the tropical grasses, although the rate of intake of the legume diets was at least twice that of the tropical grass diets. The average length: width ratio of particles from B. napus petioles and stems was 5:1. A high proportion of particles from the B. napus and D. intortum diets had a rough surface. 5. arvensis was broken into more particles per g dry matter than the legumes and B. napus, despite its very high rate of intake. Many pieces of stem of S. arvensis were not split longitudinally during chewing.