In vitro fermentation kinetics of some halophyte shrubs sampled at three stages of maturity

Relationships between in vitro fermentation kinetic parameters, chemical composition and stage of maturity were evaluated in five halophyte shrubs collected from and salty areas in south east Algeria. A gas test technique was performed using slaughtered dromedary and fistulated cow rumen fluid. Kinetics of gas production was fitted to an exponential model. Effect of maturity was significant for ash (P < 0.003), neutral detergent fibre (NDF) (P < 0.03) and acid detergent fibre (ADF) (P < 0.04). The effect of plant species was significant (P < 0.04) only for crude protein (CP) content. Fermentation characteristics increased significantly (P < 0.05) between pre-bud (March) and early bloom (May), while no significant change occurred from May to June. Observed gas production at 24 h (GAS24) was influenced by plant species (P < 0.001), maturity (P < 0.001), source of inoculum (P < 0.001) and by their interactions (P < 0.05). GAS48 was similarly affected, except for inoculum and plant species interactions. GAS24 and GAS48, potential gas production b and rate constant of gas production c were positively correlated with NDF in June (0.65 ≤ r ≤ 0.73) and negatively with ADF in March (-0.63 ≤ r ≤ -0.84) and May (-0.65 ≤ r ≤ -0.75). Chenopodeaceous shrubs Atriplex halimus, Salsola vermiculata and Sueada mollis had a high CP content (9.4-19.3% of dry matter, DM), high gas production (179.1-209.9 ml/g organic matter, OM), relatively high levels of cell wall content (45.6-67.0% DM) and high ash content (15.0-32.3% DM). All shrubs had lower in vitro fermentation characteristics than Medicago saliva used as a standard hay. The relatively high level of ADL (11.1 +/- 4.2% DM) can explain in part the limited microbial in vitro degradation of shrubs, specially in March when aerial green part of shrub was scarce. Observed and estimated kinetic parameters, apart from the constant rate, were higher (P < 0.05) with dromedary inoculum. GAS24 and GAS48 obtained with dromedary inoculum may be used to predict gas production of cow inoculum. (C) 2003 Elsevier Science B.V. All rights reserved.