Effect of Picrasma quassioides plant extract , yeast culture and monensin on in vitro mixed ruminal microorganism fermentation of wheat starch

The objective of this study was to compare the plant extract from Picrasma quassioides (EPQ), yeast culture and monensin on in vitro rumen fermentation characteristics of wheat starch. Compared with the control (no additive), EPQ decreased the dry matter digestibility and the total VFA production (P<0.05), and increased the ratio of acetate and propionate. Both EPQ and yeast culture increased the fi nal rumen pH (P<0.05), but monensin had a negative effect on decline of rumen pH. In conclusion, the addition of EPQ can effi ciently retard rumen fermentation rate of wheat starch in vitro, and increase the fi nal pH of ruminal fl uid.


INTRODUCTION
Diets rich in readily fermented carbohydrate will induce acute and chronic acidosis of ruminant.Since the Food and Drug Administration approved the feeding of ionophore-antibiotics to animals in the mid-1970s, these compounds have been used to prevent rumen acidosis and improve production performance of beef cattle.Monensin is the most widely used ionophore (Russell and Strobel, 1989).It can decrease CH 4 production (Thornton and Owens, 1981) and increase ruminal pH by decreasing volatile fatty acid and lactate production (Bergen and Bates, 1984).Yeast culture has been supplemented in ruminant diet for many years.Researchers have reported that, in some cases, yeast culture could infl uence the ruminal fermentation in vitro and then stimulated lactate uptake (Harris and Webb, 1990).Unfortunately, there were not consistent results about the effect of yeast culture in in vivo and in vitro fermentation (Martin and Nisbet, 1992).EPQ is used as herbal antimicrobial to prevent infl ammation in human medicine, which shows that the EPQ may effect on the bacteria.So the objective of this study is to compare the effects of the EPQ, yeast culture and monensin on ruminal fermentation in vitro of readily fermented carbohydrate (wheat starch).

MATERIAL AND METHODS
Wheat starch was used as a substrate for the rumen fermentation in vitro.EPQ purchased from Shengzhitang Company (Guangdong, China) was added to form a fi nal concentration of 100 mg/l mixed culture fl uid.Yeast culture product, purchased from Piotech Company (USA), was added at the concentration of 200 mg/l.Monensin was purchased from Haizheng Company (China) and added at the concentration of 3 mg/l mixed culture fl uid.
In vitro rumen fermentation was carried out with rumen fl uid which was obtained from four rumen cannulated steers fed concentrate supplement twice a day.Ruminal contents were obtained in the morning, mixed and squeezed through four layers of cheesecloth into a 1.000 ml fl ask with an O 2 -free CO 2 headspace and maintained in a 39°C water bath.Particle-free fl uid from the fl ask was anaerobically mixed (1:4) with a buffer (pH 6.5) containing the following compounds, mg/l: K 2 HPO 4 292, KH 2 PO 4 240, (NH 4 ) 2 SO 4 480, NaCl 480, MgSO 4 •7H 2 O 100, CaCl 2 •2H 2 O 64, Na 2 CO 3 4000, and cysteine hydrochloride 600 (Lynch and Martin, 2002).After mixing, 30 ml buffered rumen fl uid was dispensed in to 100 ml syringe containing 300 mg of wheat starch and different additives described previously.The glass syringes (HFT000025, Häberle Maschinenfabrik GmbH, Germany) were sealed by clips and incubated at 39°C for either 24 h (for 24 h fermentation traits) or 72 h (for 72 h gas production).Each treatment had three syringes as replicates.The next three syringes were served as blank incubation (rumen fl uid + buffer).After 24 (or 72) h, fermentation was stopped and the syringes were put into an ice-cooled bath.
After cooling, all the contents of the syringes were centrifuged (5400 g, 4°C, 15 min) for dry matter digestibility (DMD) determination.The concentrations of VFA were determined by the gas chromatogra phy procedure (Beauchemin et al., 2003) with the Agilent G 6890 Gas Chromatography.NH 3 -N concentration was measured according to the method of Broderick and Kang (1980), lactate concentration by ion chromatogra phy procedure (Dionex ICS 2500).
The data of 72 h dynamic gas production was estimated using the non linear regression procedure of SAS (1996) the model is GP=B*[1-exp (-c*(t-lag))].
The differences in pH, total and individual volatile fatty acids, lactate, NH 3 -N production as well as dry matter digestibility (DMD) and other parameters were analysed by analysis of variance using GLM procedure of SAS (1996).

RESULTS AND DISCUSSION
The dynamic change of cumulative gas production of different additives was shown in Figure 1.EPQ signifi cantly decreased (P<0.05) the rate of the gas production and increased (P<0.05) the lag time (Table 1).This might be due to the EPQ could depress the activity of ruminal microorganisms and infl uenced the fermentation, which resulting in the decreased rate of gas production.Monensin signifi cantly decreased (P<0.05) the amount of gas production and the yeast culture decreased (P<0.05) the lag time of the fermentation.The effect of different additives on ruminal fermentation characteristics in vitro was shown in Table 2. Compared with the control, EPQ and yeast culture increased the fi nal pH, and EPQ had the highest value.Some studies showed that yeast culture increased the pH during the ruminal fermentation in vitro, but there were not consistent results between in vivo and in vitro (Martin and Nisbet, 1992).EPQ decreased (P<0.05) the DMD after 24 h fermentation.This result showed that the plant extract of Picrasma quassioides decreased the activity of the ruminal microbes and then decreased the feed digestibility.The concentration of NH 3 -N was increased (P<0.05) by addition of EPQ and monensin, the greater value corresponding to the EPQ.Monensin decreased the molar ratios of acetate to propionate (P<0.05).It was in agreement with the result described by Russell and Strobel (1989).Yeast culture almost had no effect on the production of VFA.However, EPQ could signifi cantly decrease the total VFA production (P<0.05), and increased the molar ratio of acetate and propionate.Because little lactate (<1 mmol/l) was detected in the present study, the increased fi nal pH of the EPQ treatment might be due to the decreased total VFA production.

CONCLUSIONS
Addition of extract from Picrasma quassioides (EPQ) decreased ruminal fermentation rate and 24 h DMD in vitro.This plant extract showed a function in prevention of the rumen pH decline, suggesting a potential use as a rumen fermentation modulator.A deceased 24 h in vitro DM digestibility and less production of total VFA due to addition of the plant extract from EPQ indicated an alteration of rumen digestion site or extent resulting from such EPQ addition.EPQ also changed the molar proportion of individual VFA, suggesting an alteration occurring in the ruminal fermentation pattern.Further studies are needed to investigate the response of animal performance to the addition of this plant extract and its responding mechanisms.

Figure 1 .
Figure 1.The dynamic change of cumulative gas production of wheat starch added different additives

Table 1 .
The effect of different additives on dynamic traits of in vitro gas production of wheat starch means with different superscript letter within the same line differ signifi cantly (P<0.05

Table 2 .
The effect of different additives on rumen fermentation characteristics in vitro