Importance of dry matter content to voluntary intake of fresh grass forages

Abstract

Voluntary consumption (VC) of wet feed and feed dry matter (DM) was measured indoors with sheep fed 3 ryegrass and 2 tall fescue cultivars at different stages of maturity. Increasing plant maturity, indicated by increasing proportion of stem and flowerhead and of neutral detergent fibre and cellulose contents, was associated with decreasing wet feed intakes. VC of wet feed was about 15% higher with ryegrass cultivars than tall fescue cultivars. VC of feed DM was positively correlated (r = 0.89) with forage DM content at all stages of forage maturity and over a wide range of forage DM contents (12 25% DM). VC of wet feed was not affected by changes in DM content so that with forage at the same stage of maturity DM intake was increased with an increase in forage DM content. Studies with rumen fistulated sheep showed 90% of cells in eating boli are ruptured during 1 h incubation in rumen fluid in vitro or in vivo. Also VC of immature and mature perennial ryegrass was not affected when a balloon containing 1.5 I water was placed in the rumen whereas VC of chaffed lucerne hay was significantly depressed. It is concluded that VC of fresh forage is limited by a mechanism regulating intake of wet feed, not feed DM, and that DM content may be an important factor limiting nutrient intake.