Main page > News archive > Progut Info Letter 2/2008

25.04.2008

1.      Objective

The aim of the study was to investigate the effect of hydrolysed brewery yeast Progut™ on rumen microbial fermentation and microbial community structure with different silage-to–compound feed ratios. Different silage-to- compound feed mixtures were used to simulate the feeding during the whole lactation period.

2.      Materials and methods

The effect of Progut™ on rumen microbial fermentation was investigated in a rumen simulation study by Alimetrics Ltd. in Finland in 2007. An in vitro model imitating the rumen fermentation processes as closely as possible was used. Total gas production, pH, short chain fatty acid production (SCFA) and volatile fatty acid (VFA) production were measured and the total number of microbes was determined by flow cytometry. The microbial community structure was analysed by sequencing of the 16S rDNA gene. There were three different basic diets in the trial.

1)      75 % compound feed and 25 % grass silage

2)      50 % compound feed and 50 % grass silage

3)      25 % compound feed and 75 % grass silage

3.      Results

3.1.           The effect of Progut™ on rumen microbial fermentation

Addition of the hydrolysed brewery yeast (Progut™) increased rumen fermentation rate with all three silage-to-compound feed ratios (figure 1). The highest enhancement was seen during 2 to 8 hours of fermentation. In later stages the fermentation was slower and Progut™ had less effect. Therefore, it can be considered that Progut™ specifically stimulates the highest metabolic activity stage of rumen fermentation.

Similarly, Progut™ increased the production of microbial biomass with all three diets (figure 2) during the first six hours of the simulation. At 12 hours it had an effect on microbial biomass only with the highest silage diet. In the end of the simulation (24 h) Progut™ increased microbial biomass with all basic diets but the difference to control was statistically significant only with the highest compound feed diet (figure 3). The results from the microbial community structure analysis presented in 3.2. show that the increase in the microbial biomass in different stages of fermentation was caused by different microbial groups.   

Figure 1. Cumulative gas production

Figure 2. The total number of microbes at 6 hours of simulation

Figure 3. The total number of microbes at 24 hours of simulation

First six hours of the simulation was dominated by lactic acid production and only small amount of longer chain VFA’s were produced during that period. Later on, lactic acid to VFA ratio decreased in a manner that closely matches with the increase in propionate production. Thus, it seems likely that lactic acid is to large part converted to propionate. The increase in the compound feed-to-silage ratio increased lactic acid production, like expected, and thereby also propionic acid concentration in the end of the fermentation (results not shown here). 

Progut™ significantly increased SCFA production after 6 hours of simulation with the two highest compound feed ratios (table 1). There was a non-significant tendency for higher lactic acid production with Progut™ addition. However, it didn’t have any major effect on the rumen pH. At 24 hours it significantly increased SCFA and VFA production with all three diets. Increase in the VFA production at later stage of fermentation was mainly due to increased propionate production. Acetic acid and butyric acid production were less affected by Progut™ addition. Lactic acid is the main SCFA at early stage of rumen fermentation and it’s later converted to propionate by normal rumen microbes. Results from this study indicate that Progut™ improved the conversion of lactic acid to propionate. 

In the present study Progut™ increased both the production of energy and protein by increasing the short chain fatty acid production and by increasing the number of rumen microbes during the simulation process with all three basic diets (figure 4). Thus, it remarkably decreased the amount of undegraded feed.

Table 1. The effect of Progut™ on the production of SCFA with different basic diets

+    increase by 0-5 %                                           *        0.05 > p- value > 0.01

++   increase by 5-10 %                                        **     0.01 > p.value > 0.001

+++ increase by > 10 %                                        ***    0.001 > p-value > 0.0001

                                                                       ****   p-value < 0.0001 

Figure 4. The effect of Progut™ on rumen fermentation parameters

3.2.           Progut™ stimulated metabolically active microbes in rumen

To summarize the structure and function of microbial community at the three time points, starch degradation and consequent lactic acid production by the Streptococcus bovis group was the dominant process during the first six hours of simulation (figure 5) which is in line with the observed high lactic acid concentration at the 6 hour time point (3.1.). As the simulation proceeded further, also fiber degradation started to take place and microbes with cellulolytic activity, Butyrivibrio fibrisolvens and Prevotella spp., increased in proportion. The proportion of lactic acid degraders, Selenomonas spp., increased over time, in line with the concomitant decrease in lactic acid concentration and increase in propionate concentration.

When assessing the effects of Progut™ on the microbial community structure, one should keep in mind the highly dynamic nature of the simulation: the proportions of microbial groups change with the feed ratio and along the simulation time. The microbial samples taken at a certain time point integrate the history of the microbial community until that time point; however in a matter where changes in the community structure close to the sampling time affect the results more than changes with longer temporal distance to the sampling time. Progut™ had clearest effect on the number of lactate degrading Selenomonas spp. group bacteria. It tended to increase the amount of this bacteria group at 12 hours with the two highest compound feed diets and significantly increased its amount at 24 hours with the high silage diet (figure 6).

Figure 5. Relative proportions of the main microbial groups along the simulation

Figure 6. The effect of Progut™ on lactate degrading Selenomonas spp..

The stimulatory effect of Progut™ on the cellulolytic + amylolytic microbes was statistically significantly detected for the high silage treatment at 24 hour time point (p = 0.004). At this time point Progut™ increased the proportion of cellulolytic + amylolytic bacteria from < 20 % up to > 45 % with the high silage diet but didn’t have an effect with the other diets (figure 7). Overall, the results suggest that Progut™ always stimulates those microbes that are metabolically most active.  

Figure 7. The effect of Progut™ on cellulolytic+amylolytic microbial groups

4.      Conclusions

-          Progut™ significantly increased the rumen fermentation rate and the production of microbial biomass with all three silage-to-compound feed ratios during early stages of the simulation

-          It also significantly increased SCFA and VFA production with all three basic diets, affecting most on the production of propionate

-          By increasing the number of rumen microbes and by increasing the production of SCFA Progut™ improved the production of protein and energy and decreased the amount of undegraded feed. The improvement was similar with all three silage-to-compound feed ratios indicating that its effect is equal in different lactation phases. 

-          In later stages of the simulation Progut™ enhanced cellulolytic microbes and lactic acid degraders, especially with the high silage diet which was in line with the observed improvement in propionate production. Overall it seemed to favour those microbes that were metabolically most active.