Chemical composition and in vitro gas production of Brachiaria decumbens harvested at different stages of growth in the hot humid region

Abstract

The study evaluated the effect of harvesting date on the chemical composition and in vitro gas production of the botanic fractions of Brachiaria decumbens grass. The botanic fractions (leaf, stem and whole plant) of the grass at two maturities (60 and 120 days) in a Completely Randomised Design with factorial arrangement. Samples of botanic fractions at the different harvest dates were chemically analyzed for dry matter (DM), crude protein (CP), fibre concentrations and in vitro gas production (IVGP) was measured at 3, 6, 9, 12, 24, 36, 48, 72 and 96 h to estimate the volume and rate of gas production. Short-chain volatile fatty acids, microbial protein production, in vitro organic matter digestibility, and metabolizable energy were estimated from established models. Organic matter, crude fibre, NDF, ADF and ADL increased (P<0.05) with increasing maturity whereas the reverse was so for CP and ash contents (P<0.05). Significant interactions (P<0.05) between harvest date and plant fraction were present for both ‘b’ and ‘c’ attributable to treatment effects. Potential gas production ‘b’ elicited a negative response for all plant fractions across the two harvest dates as the values decreased linearly. The rate at which the gases were produced ‘c’ also induced a negative response for the leaf and whole fraction but a positive one for the stem fraction. The nutrient composition and gas production characteristics of grasses harvested at day 60 offer a better potential as high quality forage for improved intake and digestibility. The leaf fractions performed relatively better based on the afore-mentioned methods of quality assessment at both maturity periods.