Livestock yeasts have become a popular and effective additive in the feeding of ruminants. These live and bioactive additives have beneficial and significant effects in animals such as dairy cows, sheep, and goats. Yeasts, which are known as a type of probiotic, are often of the Saccharomyces cerevisiae type. They improve feed digestibility, reduce the effects of stressors, and prevent disorders such as acidosis by improving rumen conditions for the growth of beneficial bacteria and reducing the effects of bacteria with undesirable activity. Saccharomyces cerevisiae yeast in cattle nutrition leads to increased milk production and milk fat percentage, growth, and overall body health. In this article, we intend to review the mechanisms of action of yeasts and points related to their use in animal feed.
What is Saccharomyces cerevisiae Yeast?
Saccharomyces cerevisiae is the most important industrial yeast for biochemical processes in the food industry. These types of yeast are classified in the kingdom of Fungi, the phylum Ascomycota, and the subphylum Saccharomycotina. Generally, two types, Saccharomyces cerevisiae and Saccharomyces boulardii, are used in human, livestock, and poultry food industries.
Functions of Saccharomyces cerevisiae Yeast in the Rumen of Ruminants
The rumen is a highly active and dynamic microbial fermentation environment. However, like any other biological system, it requires its own optimal conditions for proper activity. Yeasts have long been used in animal feeding, particularly in dairy cows. Due to their noticeable performance, they have gained significant popularity and acceptance among farmers and nutrition specialists and have become a fixed part of animal rations. In general, yeasts in the rumen improve fiber digestion, reduce acidity, and promote better growth of microorganisms. Below, we will discuss the mechanisms of yeast action in the rumen based on scientific studies.
Creating Anaerobic Conditions in the Rumen
The feed fermentation process in the rumen is an anaerobic process. Therefore, the presence of oxygen and a high redox potential in the rumen causes a decline in bacterial performance. This is because most rumen bacteria are anaerobic, and the presence of oxygen seriously disrupts their function. Yeasts help create more anaerobic conditions by rapidly consuming oxygen and producing carbon dioxide. This is particularly important for fiber-degrading bacteria.
Reducing Lactic Acid Production
During the rapid fermentation of starch and sugars in the rumen, the pH decreases, and if this process is not interfered with, the rumen enters the cycle of acidosis. Under low pH conditions, lactate-producing bacteria such as Streptococcus bovis perform highly, and as a result of lactic acid accumulation, acidosis occurs. The reason for this is the low absorption of lactate from the rumen wall and its rapid production. Some scientific evidence suggests that livestock yeast Saccharomyces cerevisiae reduces the activity and population of lactic acid-producing bacteria through competitive mechanisms for nutrient consumption, thereby weakening the process of ruminal acidosis.
Increasing Lactic Acid Consumption
Previously, it was thought that yeasts themselves consume the lactic acid present in the rumen, but subsequent research showed that they often create conditions for its consumption by other microorganisms. Similar to lactic acid-producing bacteria, there are also lactic acid-consuming bacteria in the rumen. However, their activity is normally slower than that of the producing bacteria. Bacteria such as Megasphaera elsdenii and Selenomonas ruminantium are known as lactate-consuming bacteria. Lactate in the rumen is mainly converted to pyruvate and eventually absorbed by the animal’s body through the rumen wall in the form of propionate.
Increasing Fiber Digestion
As mentioned, yeasts improve the performance of fiber-digesting bacteria by creating anaerobic conditions in the rumen. In addition, microorganisms involved in fiber digestion, like any other living organism, require specific micronutrients such as vitamins, peptides, amino acids, branched-chain fatty acids, and other growth factors. Yeasts enhance their performance by providing these materials for fiber-digesting bacteria and fungi. Studies have shown that the performance of fiber-digesting bacteria improves in the presence of yeasts. Also, fungi, which play a fundamental role in breaking down the lignin in the cell wall, perform better with the addition of yeast. This leads to a fundamental change in improving fiber digestion.
Reducing the Rate of Starch Degradation
Studies have shown that yeasts reduce the rate of starch degradation by strengthening a specific population of protozoa (a type of microorganism in the rumen) that engulf starch and prevent its rapid digestion by bacteria. As a result, the process of lactic acid accumulation in the rumen slows down. According to some researchers, the reason for the increase in protozoa is the production of branched-chain volatile fatty acids by yeasts.
Strengthening and Stabilizing the Microbial Population
Yeasts improve rumen conditions and reduce the effects of stressors such as heat stress and dietary changes on rumen function by providing necessary micronutrients and improving general conditions for microorganisms. Findings show that using yeast in the diet of close-up and fresh cows significantly reduces digestive and metabolic disorders in early lactation. Also, in the diet of suckling calves, it has been observed that the presence of yeasts leads to faster formation of the microbial population in the gastrointestinal tract.
Physiological Effects of Yeasts on Animal Body Performance
As mentioned earlier, Saccharomyces cerevisiae yeast helps increase nutrient availability in the animal’s body by improving rumen function. Along with microbial activity, yeast contains numerous bioactive compounds that have beneficial roles in the animal’s digestive system and body.
Increasing Energy Supply for the Animal’s Body
It was mentioned earlier that Saccharomyces cerevisiae yeast in cows improves the digestion of the fibrous part. As a result, energy precursors such as propionate and milk fat producers like acetate are produced more. Therefore, yeasts in fresh cows reduce the consequences of negative energy balance.
Improving Feed Digestibility and Intake
In previous sections, it was mentioned that yeasts help digest fiber in the digestive system. Increasing the digestion of fiber or the NDF part of the diet reduces the ruminal accumulation of feed materials and increases feed intake. Also, yeasts improve the palatability of feed and increase appetite, leading to higher feed consumption. This generally offers significant advantages, especially for fresh cows facing energy supply challenges.
Increasing Milk Production and Milk Fat Percentage
Given the above, the effects of yeasts as effective enhancers of production and fat percentage in dairy cows have been observed by many specialists and breeders of these animals.
Increasing Growth in Young and Fattening Animals
The role of yeasts in increasing the growth of fattening animals is observable due to increased feed intake and better rumen function.
Antioxidant Properties
Saccharomyces cerevisiae yeast produces significant amounts of natural antioxidants. This helps animals have greater resistance during environmental stresses such as heat stress, diseases, parturition, negative energy balance, etc., when free radical levels increase. Therefore, Saccharomyces cerevisiae yeast is very helpful during times of stress.
Gut Health
The intestine is one of the vulnerable parts of the ruminant digestive system. However, it receives less attention compared to the rumen. Saccharomyces cerevisiae yeast contains beta-glucan and mannan oligosaccharide compounds in its cell wall, which, when released in the intestine, significantly enhance the health of epithelial cells and reduce intestinal health disorders.
A-Rumex as a Yeast Supplement
A-Rumex is a livestock yeast product produced by Sepehr Saman Fartak Company, composed of the highest quality strain of Saccharomyces cerevisiae yeast and supportive components such as autolyzed yeast and chelated minerals. It is an effective solution for reducing the effects of stresses and diseases and improving the performance of ruminants’ rumen.