Influence of individual and mixed extracts of two tree species on in vitro gas production kinetics of a high concentrate diet fed to growing lambs

This study was conducted to investigate effects of different doses of Leucaena leucocephala (LL) and Salix babylonica (SB) extracts, rich in secondary metabolites, and their mixture (LLSB, 1:1, v/v) on in vitro gas production and some ruminal fermentation patterns such as truly degraded substrate (TDS), short chain fatty acids (SCFA), and microbial protein production (MP) of a high concentrate diet (HCD) fed to growing lambs. The HCD contained (g/kg DM): crude protein (CP), 208; ether extract (EE), 12; neutral detergent fibre (NDFom), 364; acid detergent fibre (aADFom), 41. Plant extracts were prepared at 1 g DM/8 ml of solvent mixture (methanol:ethanol:water, 1:1:8) and added at levels of 0, 0.6, 1.2 and 1.8 ml/g DM. Rumen liquor was collected from 8 growing lambs (Katahdin × Pelibuey, LW 24 ± 0.3 kg) fed the same HCD. In vitro gas production (GP) was recorded at 2, 4, 6, 8, 10, 12, 24, 48 and 72 h of incubation. After 72 h, the incubation was stopped and the inoculants pH was determined and filtered to determine TDS. Ruminal fermentation parameters such as 24 h partitioning factor (PF24), gas yield (GY24), in vitro organic matter digestibility (IVOMD), metabolizable energy (ME), SCFA, and MP were also estimated. Tree species × extract level interaction (P < 0.05) only occurred for gas production at 24 (GP24), 48 (GP48) and 72 h (GP72) of incubation, but there were no interactions before 24 h of incubation. Relative to control, addition of extracts increased (P < 0.05) gas volume GP24, GP48 and GP72, except LLSB extract which had lower (P < 0.05) values during the first 48 h of incubation versus control (i.e., 0 ml/g DM). There was no significant impact of extracts on gas production parameters (i.e., b; asymptotic gas production, c; rate of gas production and L; discrete lag time prior to gas production), while the L tended to decrease (P = 0.073) with increasing extract dose only in LL and SB extracts. Addition of either dose of supplemental LL and SB extracts increased (P < 0.05) gas production and this increase was higher (P < 0.05) for 1.2 ml and 1.8 ml than 0.6 ml extract/g DM for GP24, GP48 and GP72. In general, gas productions were higher (P < 0.05) in SB than LL extract. There were no interaction in final ruminal pH, PF24 and GY24, while some fermentation parameters (i.e., TDS, IVOMD, ME, SCFA, and MP) were higher (P < 0.05) in LL and SB extract doses versus control. The highest two extract doses (i.e., 1.2 and 1.8 ml/g DM) increased (P < 0.05) TDS, IVOMD, ME, SCFA and MP values versus 0.6 ml/g DM. The SB extract also had higher positive impacts (P < 0.05) on rumen fermentation parameters versus LL extract. It is suggested that the individual extracts of LL and SB, but not the mixture, could positively modify rumen gas production and fermentation, which may improve nutrient utilization in growing lambs.