By Dr Chandra Kiran Sant, International Dairy management consultant, Mumbai.
Yeast is a unicellular fungi that does not reproduce via asexual spore production . The most commonly fed yeast in dairy diets is Saccharomyces cerevisiae (SC); a facultative anaerobic yeast often referred to as brewers or bakers yeast. The most common yeast products fed to ruminants are live cells or yeast culture mixtures. A yeast culture is a yeast-fermented product that contains live and dead yeast, the culture media the yeast cells were grown on, and the metabolic by-products produced by the yeast during fermentation. The process involves inoculation of a culture media (generally liquid and cereal grain raw ingredients) with live yeast cells, fermentation of the media, and drying of the fermented media. Live cell yeast products consist solely of live dried yeasts that are mixed with a carrier for feeding. Yeast is supplemented in dairy diets to improve animal performance and is considered a ‘natural’ alternative to using antibiotics. When fed to lactating dairy cows, improved milk production is the most consistent benefit reported, however increased dry matter intake (DMI) and milk fat percentage have been shown. Supplementing calves with yeast has been found to improve body weight gain and health. How yeast directly improves animal health and performance is not known although a variety of mechanisms have been suggested. These include changes in the rumen microbial population, rumen fermentation, intestinal nutrient flow, and diet digestibility. Dairy cattle research on feeding yeast has shown inconsistent responses. One explanation for this inconsistency is the wide variation in conditions across studies. This includes differences in inclusion level, type of diet fed, feed intake and the use of additional feed additives along with animal factors such as age, physiological stage, health and stress status; all of which may affect DFM efficacy.
The use of live micro-organisms as feed supplements for ruminants is not a new concept. Particularly, feeding large amounts of “beneficial” microbes to livestock under stress or confronted with a disease challenge.
Microbial products used in this manner were originally called “probiotics,” or products “for life.” However, the term “probiotic” implied a curative nature.
The feed industry, in conjunction with regulatory agencies, has accepted the more generic term of “direct-fed microbials” (DFM) to describe microbial-based feed additives. In addition, a list of accepted micro-organisms for use in animal feeds was developed.
Interest in the use of fungal direct-fed microbials in ruminant nutrition is considerable. The ban of antibiotic growth promoters in feed for production of animal foods in the European Union and some Asian countries like India has increased interest in evaluating the effect of yeast products on the gastrointestinal ecosystem, rumen microbial populations and overall animal performance.
Various feed additives are in widespread use in diets of ruminants to modulate rumen metabolism which ultimately may enhance nutrient utilization and animal performance. Yeast products such as Saccharomyces cerevisiae and Aspergillus oryzae are often utilized in ruminants to improve nutrient utilization, rumen fermentation characteristics, milk production and daily gain. Yeast additives may exert positive effects on digestibility especially fiber components, probably by stimulating the cellulolytic microbial populations in the rumen. Rumen fermentation characteristics such as increased total volatile fatty acids, stabilization of rumen pH and decreased lactate concentration might be observed due to yeast supplementation. The increase in feed utilization and improvement of rumen fermentation along with increased dry matter may also enhance milk production and animal performance. Although, the favourable responses of yeast inclusion are usually moderate in ruminant nutrition, these responses are not always observed. The discrepancies of responses of yeast inclusion as a feed additive in different experiments might be attributed to dose, type of diets, strains of yeast, physiological stage and feeding systems. Therefore, yeast products should be added in diets by taking consideration of various interaction factors to achieve the consistent beneficial responses of yeasts in ruminant nutrition.
Yeast supplementation in ruminants shows moderate beneficial effects on nutrient utilization, rumen fermentation characteristics, milk production and daily gain. Addition of some strains of yeasts in diets may also decrease methane production in ruminants. Yeasts influence positive effects on nutrient digestibility especially fiber components, probably by stimulating the cellulolytic microbial populations. Improvement of rumen fermentation characteristics such an increase in total volatile fatty acids, stabilization of rumen pH and a decrease in lactate concentration might be observed due to yeast supplementation. The improvement in feed utilization and rumen fermentation along with increased DM intake due to yeast addition may also result in increased milk yield and animal performance. But all these responses of yeasts in ruminant nutrition are always not observed. The discrepancies of responses of yeast inclusion as a feed additive in different experiments might be attributed to dose, type of diets, strains of yeast, physiological stage and feeding systems. Therefore, to obtain the consistent beneficial effects of yeasts in ruminant nutrition, yeasts should be added in diets by taking consideration of various interaction factors.
Do they really work?———-
It is clear from these research efforts that yeast product supplements can beneficially modify microbial activities, fermentative and digestive functions in the rumen.
The research has demonstrated that viable yeast product preparations can stimulate specific groups of beneficial bacteria in the rumen and has provided mechanistic models that can explain their effects on animal performance.
Fungal DFMs have been popular additions to ruminant diets for many years. In general, three types of fungal additives are available. First, some products contain live yeast (Saccharomyces cerevisiae) only or associated with their growth culture medium.
Second, other products contain S. cerevisiae and culture extracts but make no guarantee for live organisms. Third, there are fungal additives based on Aspergillus niger and Aspergillus oryzae fermentation end products that also make no claim for supplying live microbes.
The most common yeast species used in the feed industry is Saccharomyces cerevisiae. It is typically fed in dairy cattle rations to alter rumen fermentation in an attempt to improve nutrient digestion, N utilization, reduce the risk of rumen acidosis and improve animal performance.
Rumen pH regulation is a key determinant in the maintenance of an optimal rumen function. Stabilization of rumen pH in the presence of live yeast has been reported in literature.
The impact of live yeast on ruminal lactate concentration has been confirmed in several in-vivo studies. In sheep, during their adaptation to a high-concentrate diet, ruminal lactate concentration was significantly lower in live yeast-supplemented animals compared to control animals.
Consequently, rumen pH was maintained at values compatible with an efficient rumen function, as shown by higher fibrolytic activity. In dairy cows, reductions in rumen lactate concentrations have also been observed with live viable yeast.
Recent multi-study analyses performed both in dairy and beef cattle have shown significant benefits with live yeast (Saccharomyces cerevisiae I-1077) on milk yield and feed efficiency.
In ruminant animals, when forage is ingested, it is coated with a layer of air bubbles on the surface. Moreover, ruminants consuming a high-forage diet spend at least 12 hours per day eating and ruminating.
These two activities increase the amount of oxygen swallowed into the rumen. Live yeasts can utilize this oxygen for their metabolism – thus, decreasing the redox potential in the rumen, which is necessary for the survival of strict anaerobes: protozoa, fungi and bacteria.
Once the oxygen is removed, the rumen bacteria attach efficiently onto the fiber particles and digest the forage. The extent somewhat depends on the exact strain of the yeast, which are numerous. One live yeast strain (Saccharomyces cerevisiae I-1077) has been reported to increase fiber digestion.
Why should I use them?—————-
No animal – herbivore or omnivore – can digest unaided the principal structural carbohydrate of plants: cellulose.
The digestion of plant foods is always brought about by a symbiotic relationship between the herbivore animal, in this case the ruminant, and the microbiota contained in its digestive tract, and these microorganisms are the actual agents of cellulose digestion.
Moreover, modern livestock industry practices inevitably increase the risk of clinical and subclinical enteric diseases. This is mainly associated to higher stocking rates, high-energy-density diets and the possibility of horizontal transmission of diseases.
Thus, animals have become more vulnerable to harmful microorganisms. Traditional husbandry practices have relied on therapeutic drugs, i.e. antibiotics, to deal with these challenges.
Correct maintenance of the gut microbiota can be achieved by using direct-fed microbials, like yeasts, as an available alternative to reduce our dependence on traditional therapies, without sacrificing production efficiency. The concept of “probiotics,” or direct-fed microbials, is not new. It was originally used in human medicine in 1907.
How should I evaluate these products?———–
Since the early 1980s, feeding yeast products has increased in popularity, particularly in lactating dairy cows. Other common applications for these products have been to newborn calves (reducing enteric disorders), at weaning (reducing stress, improving intake) and for cows in transition (improving production efficiency).
A more recent survey indicates yeast products usage in rations for lactating cows is now around 38 percent.
Dr. Mike Hutjens, who recently retired from the University of Illinois, refers to the 4 R’s: response, return (What is the return on investment?), research and results (farm) when evaluating feed additives in a ration.
1. Response: A recent meta-analysis reported a 2.1 lbs per day milk response in lactating cows supplemented with live yeasts.
2. Return: Based on the results from the meta-analysis, and considering current milk prices and commodity prices, a minimum response of 0.25 lbs per day is required to obtain a 2:1 return on investment (ROI).
3. Research: More than 40 peer-reviewed research papers have been published in scientific literature to support the use of live yeasts in rations for lactating dairy cows.
4. What kind of a response do I expect on my farm? Two factors known to have an effect on the magnitude of the response are fiber digestibility (NDFD) and starch content of the ration. Generally speaking, a greater response is observed when the quality of the forages is compromised.
Also, live yeasts have a positive effect on rumen function because they limit acidosis in high-energy diets. Recent reports showed improved fiber digestibility, even when acidosis is not a threat.
How much do I have to feed (dose, level of inclusion)?—————
There has also been some debate on exactly how much of a given yeast product needs to be fed by the producer.
Some products on the market guarantee high numbers of live yeast cells (e.g., 10×109 CFU per g) with low recommended feeding rates (0.5-1.0 g per day), while other products are less concentrated and fed at higher levels of inclusion (more than 10.0 g per day) and suggest that live organisms are not required for beneficial effects because the end products of fermentation (metabolites produced by the yeast cells) are considered as the “active” ingredients.
Some products are concentrated and can be added to a premix, or further diluted to be top-dressed or mixed into the total mixed ration.
Most recommended doses are based on dose response studies and are yeast strain-specific. Look carefully at the label recommendations and the research data behind the product.
The effects of yeast products on animal productivity are strain-dependent. So, all yeast product preparations are not bio-equivalent in efficacy. This aspect opens a new field of research for new strains, each being more specialized in its use.
The goal of many of these research activities has been to define the application and production strategies that can optimize animal responses to yeast supplements.
Live products————
There is often confusion about the differences and similarities of Saccharomyces cerevisiae fermentation products and live Saccharomyces cerevisiae products, as both are often grouped together in reviews as yeast products and yeast. Saccharomyces cerevisiae fermentation products are different in function, responses and results to live Saccharomyces cerevisiae products.
Live Saccharomyces cerevisiae products contain live Saccharomyces cerevisiae, which can modify ruminal fermentation after colonization in the rumen. The potential effects include scavenging of oxygen, utilization of lactate, release of growth factors and competitive exclusion of pathogens.
So the responses to live Saccharomyces cerevisiae products depend on if and how well the live Saccharomyces cerevisiae can colonize in the rumen.
Another challenge with live Saccharomyces cerevisiae products is their stability, as storage length and conditions and the premix composition can alter Saccharomyces cerevisiae viability.,. As a consequence, the response to the same live Saccharomyces cerevisiae product may vary considerably.
Dried fermentation products—————-
In contrast, Saccharomyces cerevisiae fermentation products are dried end products of Saccharomyces cerevisiae fermentation grown on culture media under standardized conditions. Saccharomyces cerevisiae fermentation products are a mixture of hundreds of compounds. These compounds provide nutrients to beneficial rumen microbes and thereby promote feed utilization, feed intake and prevent pH fluctuation.
In addition, Saccharomyces cerevisiae fermentation products are rich in B vitamins, amino acids, peptides, nucleotides, yeast cell wall products, phenolic compounds and phytosterols that alone or in combination can act as antioxidants, appetite stimulants, growth promoters, inhibitors of pathogen colonization or growth and immunonutrients.
Saccharomyces cerevisiae fermentation products, however, are also not created equal. Product quality and consistency depends on the type and standardization of culture media, growing conditions and drying conditions.
Therefore, it is important to focus on the results of specific Saccharomyces cerevisiae fermentation products and how consistently they work across several studies when considering which Saccharomyces cerevisiae fermentation product to use.
The proper management strategies for dairy cattle are designed to prepare the cow for lactation and to minimize the incidence of metabolic diseases in the time of calving. To ensure a high milk production, numerous problems associated with the dry period have to be coped with. In order to overcome these problems it is recommended to use some feed additives which are a group of feed ingredients that can cause a desired animal response in a non-nutrient role such as rumen pH shift, growth, or metabolic modifier. Currently there has been a great interest in the use of probiotics for the livestock industry. Probiotic foods are a group of functional foods with growing market shares and a large commercial interest (A r v a n i t o y a n n i s et al., 2005). Probiotics, with regard to animal applications, were defined as live microbial feed supplements beneficially improving the intestinal microbial balance in host animal (I b r a h i m et al., 2010). Moreover, they have been approved to provide many benefits to the host animal and animal products. They are used as animal feed to improve the animal health and to improve food safety (S o n g et al., 2012). Among probiotics, Saccharomyces cerevisiae can optimize rumen function by enhancing food components and consequently improve the milk production performance while ensuring digestive comfort and health of the animal. The objective of this test is to determine the effect of the use of Saccharomyces cerevisiae on production of milk and its composition.
In summary, adding Saccharomyces cerevisiae fermentation product to dairy rations may improve feed intake and utilization in dairy cows, resulting in higher milk production and profitability. Further studies are needed to fully understand the optimal dosage for supplementation.
Reference:On request.
