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Jul 20, 2021

Using diet modelling to predict the dynamic effect of live yeast supplementation in ruminants

Jul 20, 2021


High output farming practices require a higher plane of nutrition, which typically includes increased levels of fermentable carbohydrates. This can put the animal at risk of developing metabolic disorders, in particular, challenges to rumen stability and sub-acute rumen acidosis (SARA). Traditionally, specific live yeasts have been used to overcome rumen challenges by increasing rumen pH to optimal levels in situations such as feed transition (weaning, grazing, step-up feeding programs) or during periods of stress (high temperatures and transportation). 

Recent research has demonstrated that specific live yeast can have a beneficial impact on fibrolytic microbial populations and digestibility of the fibre proportion of the diet. The live yeast is a valuable tool which allows maximisation of the diet, giving the farmer and nutritionist the possibility to either increase milk or meat revenue per kg of feed, or to optimise feed cost with similar revenue. Such technology can be particularly useful in maximising energy from the feed. Modelling the quantitative response of live yeast on rumen pH and fibre degradation in a feed formulation programme, can allow nutritionists and farmers to formulate for improved feed efficiency and income over feed cost (IOFC).  

An introduction to rumen modifiers

How can specific live yeast favourably modify rumen function? Could it be considered as a tool to optimise ruminant diet formulation? 

In monogastric diet formulation programmes several feed additives, for example enzymes, have been accepted for decades for improving the productive value of commercial feeds and allowing greater flexibility in feed formulation (least cost formulation). These technologies are supported by a positive documented response on the digestibility of feeds.

For ruminants, Dr C. Sniffen, from Cornell Institute, defines rumen modifiers as feed additives which alter ruminal fermentation and microbial growth, while having a positive impact on feed efficiency (Sniffen et al., 2010). Potential additives include ionophores, live yeasts, fermentation products, essential oils and enzymes. To be used in diet formulation models, rumen modifiers should be proven to have the capacity to modify some key steps of the biological process of rumen digestion. Furthermore, those mechanistic effects need to be validated by practical responses on feed efficiency and commercial production.

Key role of the rumen in digestion

  • A huge ferementer (up to 200L) with unique digestive capacity
  • Over 100 billion microbes/mL of rumen fluid
  • A complex ecosystem with anaerobic bacteria, ciliate protozoa, fungi and archaea
  • Up to 75% of the animal’s feed is digested in the rumen

Case study: live yeast as a rumen modifier

Rumen function optimisation is a key target for producers to improve overall animal production efficiency. Indeed, the rumen hosts a complex anaerobic microbiota responsible for degradation and fermentation of the main part of dietary components ingested by the animal. However, many factors can impair rumen function. In this context, microbial feed additives such as live yeasts, are an important tool to improve feed efficiency and overall performance.

Effects and modes of action of the live yeast strain Saccharomyces cerevisiae CNCM I-1077 (LEVUCELL SC, Lallemand Animal Nutrition) on rumen microbiota have been extensively studied. The main impacts attributable to this strain include; i) the stabilisation of ruminal pH, which is demonstrated to be a causal link to interactions with lactate-metabolising bacteria, ii) increase in fibre degradation and the subsequent improvement in digestibility due to interactions with plant-cell wall degrading microorganisms, and iii) improvement in rumen maturity which is demonstrated by S. cerevisiae CNCM I-1077’s action in favouring microbial establishment in young ruminants (Chaucheyras-Durand et al., 2008).

NDF degradation effect

In sacco trials demonstrate the positive effect of S. cerevisiae CNCM I-1077 on neutral detergent fibre (NDF) fraction degradability of more than 180 different forage samples, including: grass silage, maize silage, straw, rye grass hay, alfalfa hay, annual rye grass (pasture), meadow hay etc. Saccharomyces cerevisiae CNCM I-1077 is found to increase NDF digestibility by 3 to 8 units, depending on the type of forage and its own degradability (Guedes et al., 2008; Guedes et al., 2015; Chaucheyras-Durand et al, 2010, Ding et al, 2014).

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.


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 Saccharomyces cerevisiae CNCM I-1077 to stabilise ruminal pH is well-established.

The regulation of pH to non-acidotic levels also positively 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 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.

Figure 4: Rumen input prediction with 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.

The accuracy of prediction is further supported by the positive impact on ruminant zootechnical performance, practically measured for milk and meat type ruminants. Taking the example of dairy cows, in a meta-analysis considering multiple studies with dairy cows placed under conventional management, De Ondarza et al., (2010) concluded that S. cerevisiae CNCM I-1077 supplementation led to a significant average milk yield increase (P<0.001) (Figure 5). In addition, the sub-model indicated improved feed efficiency of the supplemented animals, further illustrating a better utilisation of dietary nutrients.

Figure 5: Example of effect of live S. cerevisiae CNCM I-1077 yeast supplementation on dairy cow feed efficiency: * under standard, non-stressful conditions (from de Ondarza meta-analysis); **under environmental stress (Marsola et al., 2010)

In conclusion, rumen specific live yeast represents a valuable tool which allows maximisation of the forage portion of the diet with higher levels of fermentable carbohydrates, and with limiting risk of acidosis and consequent metabolic disorders. More recent results confirm its beneficial impact on fibre microbial degradation and on promotion of an optimal rumen environment.

New opportunities can be considered with documented live yeasts within dynamic models to maximise milk and meat revenue per kilo of feed, or to optimise feed cost with a similar revenue.