ActiSaf^® in High Producing Dairy Cow Diets

Digestion of feedstuffs of ruminants occurs predominantly in the rumen, through fermentation by microbes rather than digestion by the animal itself. The rumen contains approximately 150 billion microorganisms per teaspoon. They consist of more than 500 species of bacteria, 40 species of protozoa, 30 species of fungi, and around six species of methanogenic archaea (single-celled prokaryote microorganisms). Those microorganisms digest around 70-80% of the feed through fermentation and transform it into microbial protein and volatile fatty acids (VFA). Microbial protein is the major source of protein for the cattle and contributes up to 75% of the total protein supply while the VFA are the main energy source for the ruminants. In order for the rumen to be properly functioning it needs to maintain a stable environment for its microbiota with strictly defined parameters. Ideal rumen parameters include a temperature range of 100.4 - 104° F, pH 6-7 and anaerobic environment (no oxygen).
Rumen pH is one of the most critical determinants of rumen function particularly for the rumen cellulolytic bacteria that fail to grow at pH 6.0 and below. Rumen pH falls as a result of enhanced fermentation due to increasing concentrate in the diet. The drop in pH inhibits degradation of the fibrous components of the diet and this is the cause in part of the negative associative effects between forages and concentrates. Controlling the rumen pH is very important for maintaining a proper balance between the rumen microbes. Controlling only the pH in the optimum range of pH 6 -7 is not enough maintain cellulolytic microbial activity.
Redox Potential (Eh) is another, more complex indicator that is directly linked to microbial growth and activity. Microorganisms gain chemical energy for growth and sustenance through electron-transfer reaction such as respiration, photosynthesis, and fermentation. Redox potential (Eh) is characterized by the electrons transfer between species in a liquid medium. Each bacterial species has optimal growth in certain Eh range, which allows us to monitor the shift of bacterial activity in a medium with mixed bacterial population. When oxygen dissolves in a medium, like the rumen, the organic compounds present become more oxidized and the medium exhibits a positive redox potential. Just as the transfer of hydrogen ions between chemical species determines the pH of an aqueous solution, the transfer of electrons between chemical species determines the reduction potential of an aqueous solution. The presence of oxygen disturbs this process greatly by oxidizing the environment. In the rumen the microbial growth consumes the oxygen and the medium moves towards a more negative redox potential.
The strict anaerobes like the fiber digesting and lactate fermenting bacteria in the rumen require the medium to be kept at a very low (negative) potential (around -180mV) for their optimal growth. There is close relation between rumen pH and Eh and the changes in one of those parameters leads to a change in the other. This is due to the fact that Eh depends on the type of the most active bacteria in a given moment, and the pH depends on the final metabolites of those bacteria (VFA, Lactate…). Both parameters show, in a different way, the rumen microbial activity and growth. A change in the diet can impact the rumen ecosystem balance, leading to a shift in the rumen fermentation and bacterial populations.
ActiSaf, as a dietary feed additive, can be used as a tool to enhance ruminal reducing conditions (Eh or Redox Potential). This ability enables ActiSaf to be a potent modulator of ruminal Eh and differentiate itself from buffers such as sodium bicarbonate. Sodium bicarbonate added to diets of high yielding dairy cows has been shown to increase rumen pH (see graphc 2). However unlike ActiSaf the buffer has limited effects on lactic acid levels in the rumen and is much less effective at improving ruminal reducing status (see graph 3)

The Bottom Line
The rumen is the site of degradation, digestion and microbial fermentation. The most important function of the rumen is the ability to ferment fiber which is dependent on the presence and growth of certain types of bacteria. Rumen bacteria involved in the digestion of fiber require an optimal pH range of 6.0 to 7.0. This pH range is where the fiber degrading bacteria thrive, and degrade the fibers to volatile fatty acids used by the animal as the main energy source for maintenance and production. At a pH of 6.4 the rumen bacteria degrade about 55% of the fiber; whereas, at a pH of 5.6 this falls to around 35%.
Dairy producers and nutritionists commonly use feeding strategies to reduce the occurrence of subacute ruminal acidosis (SARA). Sodium bicarbonate and ActiSaf (live yeast) are two such feeding strategies that can be implemented to help stabilize ruminal pH; however, their mode of actions are quite different. Sodium bicarbonate seems to act only as an exogenous buffer. ActiSaf acts to reduce the accumulation of lactate, increases ruminal pH and enhances fiber digesting bacterial numbers by inducing a lower ruminal redox potential.

Reference Pinloche et al.,2010. Use of 454 Life Science sequencing technology to assess the effect of yeast versus sodium bicarbonate on the rumen microbiota. Rowett-INRA Gut Microbiology Conference. June 23-25, 2010. Aberdeen, Scotland.
Marden, J.P., Julien, C. Montells., Auclair, E., Moncoulon, R., and Bayourthe, C. (2008). How does live yeast differ from sodium bicarbonate to stabilize ruminal pH in high-yielding dairy cows? J. Dairy Sci. 91, 3528-3535