influences the fibrolytic flora and digestibility performance of multiple raw materials. Indeed, lower rumen pH decreases NDF digestibility (P. Noziere et al., 2010, D. Sauvant (personal communication, synthesis of literature data) (Figure 3).
Figure 1: Overview of Saccharomyces cerevisiae CNCM I-1077 documented effects in the rumen (over 100 scientific communications on this yeast strain).
The mechanism of action of Saccharomyces cerevisiae CNCM
I-1077 on fibre degrading activities is based on stimulating and encouraging the colonisation of specific rumen bacteria and fungi, promoting substrate access. A huge portion of the rumen cellulolytic flora is considered as strictly anaerobic. Oxygen scavenging by live yeast in the rumen is an advanced mode of action for higher fibrolytic activity (Figure 2).
Figure 3 : Impact of the rumen pH on the NDF digestion rate of a raw material (from Fox et al., 2003).
Diet Modelling Significant progress has been made in model refinements over the past years, through the inclusion of biological and dynamic pathways for ruminant digestion. These non-linear refined models provide a path for innovative formulation systems, which offer opportunities to fine- tune the prediction of the nutritional values of diets, including potential sub-models for a rumen modifier. In the case of Saccharomyces cerevisiae CNCM I-1077, prediction
of nutrient digestibility can be made through rumen input (coupling effect of pH and NDF digestibility). The response will vary with forage types (NDFd effect) and rapidly fermentable carbohydrate concentration (rumen pH effect) (Figure 4). As an example, on a TMR maize silage based dairy diet, innovative biological sub-model Cornell Net Carbohydrate and Protein System (CNCPS) can predict an increase of milk production, and of milk per kilo of dry matter intake (DMI), of up to 4% with S. cerevisiae CNCM I-1077.
Figure 2: A proposed scheme for mode of action of S. cerevisiae CNCM I-1077 on fibre degrading communities (Chaucheyras- Durand et al, 2016).
Rumen pH effect Rumen pH is correlated to the level of fermentable carbohydrate content of the diet. Saccharomyces cerevisiae CNCM I-1077 has a well-documented effect on rumen pH, which has been recorded in a dataset composed of multiple diets containing different forage types. Results show treated cows maintained higher ruminal pH compared to the control. The capacity of live yeast Saccharomyces cerevisiae CNCM I-1077 to stabilise ruminal pH is well-established. The regulation of pH to non-acidotic levels also positively
Figure 4: Rumen input prediction with a rumen modifier. FEED COMPOUNDER JULY/AUGUST 2021 PAGE 33
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