Effect of Saikosaponin on rumen gas production, volatile fatty acid concentrations and microbial populations in vitro

Abstract Text:

There has been increasing interest to exploit bioactive saponins for improving rumen metabolism. This experiment was conducted to investigate effects of Saikosaponin (SSA) on rumen gas production, volatile fatty acid concentrations and microbial populations using batch cultures in vitro. It was anaerobically incubated in triplicates together with 0.5 g TMR, 50 mL basal media and 25 mL rumen fluid obtained from rumen-cannulated lactating Holstein dairy cows. Four treatments consisted of supplemental SSA at 0 (control), 0.25, 0.5 and 1.0 mg/g of dry matter，which were assigned randomly to 5 of 20 incubation bottles. Cumulative gas production (GP) was continuously measured in an automated trace gas recording system (AGRS-III, Beijing) at 39 ℃ during 48 h of incubation, after which the pH values were measured immediately and 10.0 mL of culture fluid sample were kept for analysis of volatile fatty acids (VFAs) by a gas chromatographic and the copy number of rumen bacteria populations by quantitative RT-PCR with species-specific PCR primers amplifying partial 16S rDNA regions. Data were analyzed using GLM procedure of SAS 9.2. Results revealed that SSA did not affect GP kinetics and fermentation gas pattern, while the increase of SSA addition improved the total gas production (131.78^a, 112.56^ab and 123.50^ab vs. 107.50^b ml/g DM, P < 0.05) and dry matter degradability (53.49^a, 50.36^ab and 51.83^ab vs. 48.67^b %, P = 0.07) compared with the control. The concentrations of acetate (54.88^a, 53.82^a and 54.00^a vs. 52.13^b mmol/L, P < 0.05), propionate (20.83^a, 20.32^ab and 20.25^ab vs. 19.74^b mmol/L, P < 0.05) and total VFA (91.58^a, 89.19^a and 89.34^a vs. 86.53^b mmol/L, P < 0.05) were increased, whereas molar proportions of acetate to propionate ratio were not influenced by supplementing SSA. There was no treatment effect on Ruminococcus flavefaciens and Butyrivibrio  fibrisolvens, while the relative copy number of the following bacterial species: Ruminococcus albus, Prevotella ruminicola, Anaerovibrio lipolytica, Streptococcus bovis and Fibrobacter succinogene were increased (P < 0.05) compared to the control. Overall, SSA supplementation improved gas production, VFA concentrations and major microbial species in the culture fluid in vitro, therefore Saikosaponin may be beneficial to manipulate rumen microbial fermentation in vitro.

Keywords: microbial populations; Saikosaponin; volatile fatty acid