In vitro rumen fermentation kinetics and nutritional evaluation of Kochia indica as affected by harvest time and cutting regimen

Branches of Kochia indica were hand-cut after 60, 90 and 120 days of planting (DAP) at 15 or 30cm distance from the tip (cutting length). The plants were at a vegetative stage for 60 and 90DAP, while, for 120DAP, they were at flowering stage. The nutritive value of the experimental plant samples was evaluated by determination of the crude protein (CP), buffer soluble nitrogen (BS-N), buffer soluble non-protein nitrogen (BS-NPN) and cell wall constituents (neutral-detergent fiber; aNDF, acid-detergent fiber; ADF and lignin (sa)). In vitro digestible organic matter (IVDOM), metabolizable energy (ME), microbial nitrogen (MN) and biomass (MBM) production were also estimated in the experimental samples after their incubation with rumen fluid for 96h in the absence or presence of polyethylene glycol. The characteristics of fermentation (initial gas production; a, gas production during incubation; b, potential gas production; a + b, fractional rate of gas production; c) were assessed using an in vitro incubation technique with rumen fluid. There was a negative effect of harvest time on all the studied nutritive parameters and fermentation characteristics. The values of CP, BS-N, BS-NPN, MN and MBM declined and concentrations of aNDF, ADF and lignin (sa) increased between early harvest time after 60DAP and late harvest time after 120DAP and between cutting length at 15cm and 30cm (P<0.05). IVDOM were positively correlated with BS-N and BS-NPN but negatively correlated with aNDF and ADF. Cutting treatments negatively affected all the studied nutritive parameters and fermentation rates. There were no differences in the values of IVDOM, ME, MN, MBM, fermentation characteristics and gas production over 96h due to add of PEG (P<0.05). The greatest proportion of gas production occurred between 6 and 24h of incubation. C values were negatively correlated with cell wall constituents but positively correlated with CP, BS-N, BS-NPN, MN and MBM. The amount of MN produced from 100mg substrate amounted to 1.9 or 1.4mg at early maturity stage and 1.1 or 0.8mg at late stage for cutting lengths performed at 15 or 30cm, respectively. Microbial nitrogen and MBM production were negatively correlated with cell wall constituents and gas production but positively correlated with CP, BS-N and BS-NPN. Results revealed that, the harvested branches of K. indica at the vegetative stage were better in terms of nutritional value than those harvested at flowering stage.