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Yeast Supplements

Promote rumen function with the right type of Saccharomyces cerevisiae product.

The history between humans and yeasts goes back to our earliest records of civilization. Saccharomyces cerevisiae, used since the dawn of time to ferment grains for alcoholic beverages and to generate the carbon dioxide that gives bread its lift, is now established as one of the key feed additives routinely supplemented in cattle.  

Digest forage 

What makes this yeast so effective in ruminant production relates to the animal’s ability to digest forage. Cattle itself does not digest the cellulose nor the fiber in forage. Animals do not possess the required enzymes themselves to break into this raw form of carbohydrate energy. To see the organisms responsible for the digestion of forage, we need to use a microscope.  

Microbial community 

The vast community of rumen microbiota surround, adhere to and invade forage particles leaking a suite of enzymes that unlock the potential of forage. The host ruminant in turn feeds off the products released by fiber- and cellulose-digesting bacteria or are made available when the bacteria are themselves consumed by other microorganisms. 

How yeast promotes rumen function 

Yeast cattle feed supplements work by aiding the work of these digestive bacteria. They can do this in a variety of ways. One way that is often claimed for live yeast supplements is the scavenging of oxygen which might help promote an anaerobic condition in the rumen that would aid the growth and activity of the beneficial rumen bacteria driving forage digestion.  

A drawback to this mechanism is that yeast activity in the rumen may be limited under lower rumen pH conditions and that there can be a wide variety of rumen organisms that can also scavenge oxygen. 

Another yeast supplement mechanism is to stimulate the growth and activity of forage digesting microbiota through prebiotic bioactives. A prebiotic approach differs from a live probiotic approach to supplementation. It can be more convenient because storage, incorporation into feed and processing with heat such as pelleting or extrusion is not a problem.  

The stimulatory effect on rumen microbiota is not related to oxygen scavenging by the yeast itself but rather the triggering of enhanced bacterial activity through the bioactives such as ß-glucans and mannan-oligosaccharaides. These well-established prebiotics come from the cell wall of yeasts. There is also evidence that these same bioactives can also reduce pathogen binding onto the gut epithelium and perhaps reduce inflammatory responses in ruminants. 

Types of Yeast Supplement 

One of the main differences between yeast supplements available in the market is simply whether the yeast is alive or not. Within the non-live yeasts however, there is also a variety of methods of the yeast being degraded and, in some cases, the yeast cell wall materials (the prebiotic bioactives) being made more available.  

Cell walls can be hydrolysed by acids or even strong alkaline conditions, or the yeast could be heat inactivated or put under such pressure that the cells might burst. A particularly effective method is autolysis in which the yeasts own enzymes break down the cell walls. The conditions for autolysis can be optimized to increase the extent to which the cell walls are “lysed” or broken down. 

Autolysis 

A standardized autolytic degradation of the yeast cell content provides functional components such as the ß-glucans and mannan-oligosaccharide cell wall compounds, ribonucleic acid (RNA), nucleotides, amino acids and peptides (amino acid chains) in a pre-digested form. These bioactive components serve as nutritional sources for beneficial anaerobic rumen microbes such as fiber- and cellulose digesting bacteria that digest the forage driving ruminant nutrition as well as stimulating lactate-utilizing bacteria thus helping avoid acidic rumen conditions such as sub-acute rumen acidosis (SARA). 

Benefits of yeast products for cows 

The stimulation of these beneficial bacteria as well as the avoidance of overly acidic conditions that limit the activity and survival of fiber- and cellulose-digesting bacteria can improve feed intake, and the availability of energy, protein and other nutrients from that feed. The animal health and performance benefits from a good rumen fermentation and condition are multiple. 

The production of volatile fatty acids drive growth in beef cattle and milk production in dairy cows. Acetate, propionic acid and butyrate are all required as the main energy sources in ruminants. The microbial cells and fragments that pass through the rumen from a healthy rumen microbiota also provide a substantial proportion (more than half) of the amino acid nutrition that cattle require to build protein. 

Good fiber-digesting bacterial activity can aid the breakdown of natural toxins including some mycotoxins in the feed. Furthermore, butyric acid is produced in the rumen by some of the fiber-digesting (e.g. the aptly named Butyrovibrio fibrisolvens – roughly translates as fiber-dissolving, butyric-acid-producing vibrating bacteria) and lactate-utilizing (e.g. Megasphaera elsdenii) bacteria, and this stimulates rumen papillae that in turn aid the uptake of volatile fatty acids into the ruminant’s bloodstream. This both provides nutrition to a cattle and moderates the rumen pH. 

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