Abstract
Tropical grasses generally show the lower dry matter intake of livestock than temperate grasses. In this study, we
investigated NDF digestibilities which might have been recognized as one of the factors for the intake of livestock in some
tropical grasses, and compared to that of Italian ryegrass (Lolium multiflorum Lam.) which is most commonly cultivated
as an annual temperate grass. Four commercial cultivars (Natsukaze: Panicum maximum, Callide and Katambora: Chloris
gayana, Kennedy: Brachiaria ruziziensis) were cultivated and harvested at four developmental stages (Plant height 50
cm, boot leaf, beginning of heading, 10 days after heading). The structural cell wall components (NDF, ADF, ADL), NDF
digestibility and crude protein (CP) were analyzed. Additionally the ratio of leaf blade weight to total plant weight was
measured.
Under the longer cutting intervals the NDF digestibilities analysed using artificial rumen technique method at different
incubation periods (12, 24, 48 and 72 h), decreased and NDF contents increased. The increase in NDF contents might
have induced by the increases in ADF and ADL contents and the decreases in CP and the ratio of leaf blade weight to total
plant weight. NDF digestibilities of all tropical forage grasses were lower than that of Italian ryegrass under all developmental
stages. In addition, the differences were expanded as the developmental stages were advanced. NDF digestibilities
of all tropical grasses under 24h incubation were lower than that of Italian ryegrass by 10 - 38% at all developmental
stages. Subsequently, the differences were decreased by 1 - 26% under 48h incubation at all developmental stages. These
results indicated that NDF digestion rate of tropical grasses at the early incubation period especially within 24h were lower
than that of temperate grass regardless of developmental stages. In conclusion, the lower NDF digestibilities of tropical
grasses might cause the lower dry matter intake of livestock.
