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

Abstract

Branches of Kochia indica were hand-cut after 60, 90 and 120 days of planting (DAP) at 15 or 30 cm distance from the tip (cutting length). The plants were at a vegetative stage for 60 and 90 DAP, while, for 120 DAP, 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 96 h 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 60 DAP and late harvest time after 120 DAP and between cutting length at 15 cm and 30 cm ( 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 96 h due to add of PEG ( P<0.05). The greatest proportion of gas production occurred between 6 and 24 h 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 100 mg substrate amounted to 1.9 or 1.4 mg at early maturity stage and 1.1 or 0.8 mg at late stage for cutting lengths performed at 15 or 30 cm, 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.