SHEARING FORCE OF ALFALFA STEMS AS AFFECTED BY SEEDING RATE

Physical properties of forages may provide a simple method of predicti ng animal voluntary feed intake. Physical measurements, such as sheari ng force, may indicate the resistance of the forage to particle breakd own during mastication. The objective of this study is to determine th e effects of seeding rate on the physical characteristics and cell wal l chemical constituents of alfalfa (Medicago sativa L.) stems, and to relate these characteristics to shearing strength. Stems of eight alfa lfa cultivars (120, Legend, Multiking 1, OAC Minto, Saranac, Vernal, V ertus, WL320) seeded at 6, 12 and 24 kg hag(-1) were harvested in the first and second production years and divided into three 16 cm segment s: top, middle and bottom, and the force required to shear each segmen t was measured using a modified Ottawa Texture Measuring System. For b oth years, shearing force, segment weight and stem diameter measuremen ts generally decreased as seeding rate increased when measured at the middle and bottom shearing segments on the stem, but this was not obse rved for the top shearing segment. Effect of seeding rate on differenc es in segment weight and stem diameter among cultivars was variable am ong years and stem segments. Concentrations of cell wall constituents in stems were not influenced by seeding rate, and these influenced she aring force to a lesser extent than physical characteristics. Shearing force was directly related to the diameter and weight of the stem. Be cause of the associations between shearing force and diameter and weig ht, physical characteristics of the stem may influence forage breakdow n during mastication independently, and to a greater extent than cell wall chemical constituents.