Physical structure of twelve forage species in relation to rate of intake by sheep

Abstract

SUMMARYIn order to understand better the relationship between plant physical structure and rate of intake, twelve plant species were compared: Trifolium repens L., Medicago sativa L., Onobrychis viciifolia Scop., Desmodium intortum (Mill.) Urb., Brassica napus L., Spergula arvensis L., Lolium perenne L., Lolium multifiorum Lam., Festuca arundinacea Schreb., Chloris gayana Kunth, Cenchrus ciliaris L. and Zea mays L. The effects of early as opposed to late harvesting were compared. Plants were grown in a heated glasshouse in each of 2 years, examined for morphology, anatomy, neutral detergent fibre and digestibility, and fed to sheep for 1-min test periods to record rate of intake.Rate of intake was in the order tropical grasses < temperate grasses < broad-leaved species < S. arvensis. The range was wide: from 4·6 g dry matter/min with C. gayana to 15·6 g with S. arvensis. The lowest rate of intake was associated with the possession of a large number of veins, close together, in parallel lines (tropical grasses); a rather higher rate was associated with fewer veins, further apart, in parallel lines (temperate grasses); the next to the highest rate was associated with broad leaves, which had a network of veins; the highest rate was associated with thin stems containing thin vascular bundles. L. perenne, L. multifiorum, C. gayana and C. ciliaris were similar in the thickness of large and small leaf blade veins and leaf sheath veins. F. arundinacea and Z. mays had rather thicker veins. T. repens, 0. viciifolia. D. intortum and B. napus were similar in the thickness of petiole vascular bundles. Neutral detergent fibre was lowest in B. napus and highest in C. gayana and C. ciliaris. In vitro digestibility was highest in B. napus and lowest in D. intortum.