The effects of various probiotic yeast strains on ruminant performance.
The main purpose of yeast supplementation is to treat rumen microbial dysbiosis which may enhance the nutrient utilization leading to enhanced animal growth and productivity. Yeast improves rumen ecosystem by two ways: by direct production of digestive enzymes and growth stimulator and by promoting the growth and function of beneficial microbiota. Yeasts have potential to produce metabolites, which stimulate the growth, like rumen acetogens and antimicrobial compounds which inhibit potential pathogens. The yeast probiotic impact on animals depend on different interacting factors including animal breed, supplemented dose, type, diet, strain, physiological stage and feeding system. In the situation of a high feed cost all over the world, probiotic yeast gives a useful nutritional strategy which allows increasing diet digestibility and consequently enhances the performance in ruminants in cost-effective manner. Many yeast culture-based products are commercially available worldwide, but their effectiveness as probiotic dietary supplement in a particular breed is mostly questionable. Therefore, exploration of the new indigenous probiotic strain is of great interest in this context. The probiotic strains of same ecological origin may be more compatible with rumen microbiome giving maximum outputs. Moreover, the breed specific probiotic yeast is an economical and viable option for farmers to overcome the effects of malnutrition.
- indigenous probiotics
- gastrointestinal tract
- rumen microbiota
Ruminants can eat different types of feed that are digested by microbial biomass resulting in better metabolism, which ultimately impacts the dairy animal productivity. The microbial flora in the gastrointestinal tract (GIT) has a major impact on the productive efficiency, health status, and well-being of the dairy animals [1–3]. The diversity and function of ruminal GIT microbes are very important in feed digestion. The way the nutrients are digested in GIT in ruminants have a crucial impact on growth, health, and productivity . The GIT inhabits multifarious microbial diversity that helps in generating impassive response regarding nutritious health, physiology, and productivity of animals . The existing gut microbiota regulates food safety through the shedding of pathogens, interaction with organisms and resource competition in the GIT . Gastrointestinal tract microflora aids in stimulation of the immune system that acts as a barrier against infectious pathogens. It also restrains the injurious and pathogenic bacteria in gut colonization . Different strategies have been used to enhance the microbiota of gastrointestinal tract, which ultimately affect the production potential and growth efficiency of dairy animals. Nowadays, the improvement of microbiota of the gastrointestinal tract by using probiotic has become a useful and economical method to enhance the health and productive performance of animals. A live microorganism which beneficially influences the host by improving microbial flora of its intestine is called probiotic . Numerous microorganisms have been sanctioned as probiotics that are used in diet of ruminants to upgrade nutrient utilization and animal performance . Bacterial probiotics give better results in young calves, chickens, and pigs, whereas yeast/fungal probiotics are effective in adult ruminants . During the last decades,
2. Probiotic yeast
Yeasts are eukaryotic microorganisms and are different from bacteria from the structure and functional aspects . Yeasts are facultative anaerobes and differ in terms of their location, shape, reproducing activities, subtracts they utilize and are highly resistant to different antibiotics, such as sulfamides and other antibacterial substrates . The resistance capability of the yeast cells is natural and genetically encoded. This resistance cannot be changed or transmitted to other microbial species. The size of the yeast cell (5 × 10 μm) is also higher than bacteria (0.5 × 5 μm). The study of antagonistic yeast to block bacterial pathogenicity in the early stage of development is mainly due to following steps; (1) competition for nutrients, (2) pH changes in the medium, (3) high concentrations of ethanol production, (4) secretion of antibacterial compounds and release of antimicrobial compounds (toxins or “mycocins”). However, the effectiveness of probiotic organism is viewed as population-specific due to variation in gastrointestinal microbial flora, feeding habits, and precise interaction between host animal and microbes. As most of the probiotic yeast strains accessible in the market are of Western or European origin, hence, there is a dire need to explore new indigenous probiotic strains. Yeast cells produce many important fermentation metabolites and different types of important minerals and enzymes that make it useful and highly nutritive feed supplement for ruminants [25–27]. It also provides improved production, reduced digestive problem, and better health in cost-effective manners.
3. Understating the ruminal gut microbiology for development of new target-specific probiotic strain
Uses of molecular techniques have changed the study of the rumen ecosystem . A better understanding of the rumen microbiology is an important step to select and prepare a new yeast strain affecting on functional-specific microbes. Ruminants’ stomach consists of reticulum, rumen, omasum, and abomasums . The rumen is an anaerobic chamber that harbors an immense diversity of microbial community including bacteria, archaea, fungi, and single-celled ciliated protozoa (Figure 1) .
This microbial ecosystem has been used for better feed digestion. Bacteria are numerous microbes in rumen . Mostly bacteria are associated with feed; some are free living, attached with mucous membrane and associated with fungi and protozoa. The shape of rumen bacteria are mostly cocci, rod spirochete budding, and filamentous. Rumen bacteria are 1–2 μm in size. The majority of the rumen bacterial species are Gram-negative. The structure of this microbial community is influenced by many factors, including host species, age, seasons , type of feed, geographical location, and whether the animal has received any treatment . The balance in rumen microbial flora plays a crucial role in feed utilization and could result in better productivity . The rumen microbial profile directly depends on the type of feed . Ruminants can eat from different types of feed sources that are digested by microbial biomass, which helps in better metabolism . This ultimately impacts the productivity of dairy animals. The feed microbial flora could be managed by using beneficial microbial supplementation. The management and modification of ruminal fermentation to improve animal performance have been the main objective of several studies on ruminant species. From this line of research, we will use method to manipulate the rumen fermentation for improving nutrient utilization and productivity of animals. The banning of the use of antibiotics as animal growth promoters in the European Union in 2006 has increased the demand from producers for alternative feed additives that can be used to manipulate the ruminal fermentation and improve animal production [31, 35, 36]. The modulation in the rumen population for better nutrients metabolism can be achieved made by manipulating the feed, antibiotic and some microbial inoculants. The diet-shift effect such as high-forage diet, increases the rumen pH and consequently improves the stability and viability of cellulolytic and hemicellulolytic bacteria and protozoa. On the other hand, high-concentrate diet that decreases the rumen pH, resultantly decreases the cellulolytic and hemicellulolytic bacteria and increases the amylolytic bacteria and lowers the rumen protozoa. Microbial inoculants may alter the stability and viability of microbial population of the rumen and hindgut in a better way.
4. Role of probiotic yeast in ruminant nutrition
The balance in rumen microbial flora plays a crucial role in feed utilization and could result in better animal productivity . Several hypotheses concerning the mode of action of probiotic yeast in animal nutrition have been proposed; however, a majority of them emphasize positive effects by modifying rumen microbial population. The first and most widely supported mode of action is that the yeast stimulates the growth of bacteria (cellulolytic, amylolytic, and proteolytic) and protozoa [38, 39]. The rumen dissolved oxygen (O2) can be measured in situ . Loesche  found that a majority of rumen microbial flora are highly sensitive to O2. Probiotic yeasts remove oxygen from rumen and provide a better anaerobic environment for bacterial growth . Sixteen liters of oxygen can enter inside rumen daily, by the mean of feeding, rumination, and salivation . Inside rumen, yeast cells use oxygen for their metabolic process. Freshly ingested feed particles have sugars and small oligosaccharides. Probiotic yeast metabolizes these small particles and produces peptides, polypeptides, and amino acids. This respiratory activity of probiotic yeast lowers the oxidation-reduction potential inside rumen . A negative change in the redox potential (−20 mV) has been observed in rumen with probiotic yeast addition . This change gives a better anaerobic condition inside rumen . Aforementioned environment helps in the protection of rumen bacteria from damage by oxygen and stimulation of growth of cellulose degrading bacteria [45, 46]. These conditions will also be helpful in the cellulose degrading process (cellulose digestion). Respiratory-deficient mutants of probiotic yeast cannot stimulate bacterial growth. As we mention earlier that O2 scavenging property of yeasts is very important for growth of rumen microbial biomass, hence, this O2 scavenging property should be considered when probiotic yeast is selected for ruminants (Figure 2).
Probiotic yeasts have beneficial effects on the lactate-metabolizing bacterial species.
4.1. Role of probiotics in the establishment of rumen and hindgut micro-flora establishment
The key of the rumen development is to provide supporting conditions to the microbiota to ensure its optimal establishment. It has been well studied that live yeast can help in establishing different types of micro-flora in neonate by positively modulating rumen colonization, by important functional microbial population. A newborn ruminant digestive system is sterile but with passage of time when they contact with their mother and other animals, they get microbes from their saliva and feces . In contrary, the mother and her young connection are more common in small-scale farming systems. On the other hand, in intensive dairy farming systems, the neonate is alienated from the mother and is fed on solid feeding that provides a negative situation in the development of rumen microflora . The early maternal separation has a negative effect on the rumen colonization by important microbial species. This negative situation leads to poor rumen microbial development making the neonate to suffer from different digestive diseases like diarrhea. Different diseases of digestive system are most important factors of low income heifers rearing. It has been well studied that live yeast culture can help the establishment of key microbial communities (
4.2. Effect of yeast and yeast cultures on rumen fiber digestion
Fiber is non-digestible polysaccharides (a complex form of carbohydrate) . In nutrition, the term fiber defines as a component of plant that is not digestible by mammalian enzyme . Cellulose, hemicellulose, and lignin are the primary components of fiber. Cellulose and hemicelluloses constitute 15–70% of most ruminant diet . Cellulose is the most abundant carbohydrate in plant cell wall. Chemically, cellulose is made up of linear chains of sugar molecules. In cellulose, glucose molecules are linked together in a β-1,4 links, and this linkage can only be digested by microbial cellulolytic enzymes (Table 1).
|Strain||Diet type and dose||Animal type||Effect||References|
|3 kg concentrate feed, 8 kg silage and 20 kg fodder|
3.13 × 1007 (CFU/g) yeast
|Lactating cows||1. Increase fiber digestibility and improve milk and its fat contents|
2. Improve gastrointestinal tract microbial balance
|1 g/kg as fed|
High concentration or low concentration diets
2.5 × 109 (CFU/g)
|Dairy Holstein heifers||1. Improved feed efficiency of HC-fed heifers.|
2. Yeast culture increased dry matter digestibility in HC- and LC-fed heifers
|1 × 1010 CFU/head/day|
Total mixed ration (TMR)
|Non-lactating dairy Holstein cows||1. Enhanced rumen fermentation|
2. Lower CH4 emissions
|4.5 × 109 CFU|
High starch low starch diet
|Holstein heifers||1. Positive effect on DM, NDF, ADF, and hemicellulose digestibility|||
|Dry yeast (CNCM-1077, Levucell Sc 20. Sc, Lallemand, animal nutrition)||0.5 g/hd/day|
basal diet consisting
|Holstein dairy cows in late lactation||1. Decreased time spent in subacute rumen acidosis|||
|Levucell SC 10 ME||Maize silage, 1 × 1010 CFU/g yeast||Holstein dairy cows in Non-lactation||1. Lower the risk of rumen acidosis|
2. Increased fiber degradation of low quality maize silages
|Balanced TMR or pasture|
2.5 × 109 CFU/g yeast
|Multiparous dairy cows||1. Improve the metabolic status|||
Cellulose makes up about 40% of plant cell walls. Hemicellulose also can only be digested by microbial enzymes because it also has β-1,4 linkages. Hemicellulose has a strong negative effect on fiber degradation because of close association with lignin . The rumen is an important part of the ruminant’s stomach because cellulose is broken down into simple sugar that can be used by the animal body inside rumen. The rumen represents a mobile, self-sustaining fermentation system for plant material [67, 68]. It is a complex microbial ecosystem that contain many types of microorganisms such as, bacteria (1010–1011 cells per ml), protozoa (104–106 per ml) and fungi species (103–105 zoospores per ml) [69, 70].
4.2.1. Rumen fibrolytic bacteria
Rumen bacteria (1011 viable cells per ml) dominate the fermentation, both in terms of numbers and metabolic processes. The rumen bacteria are 99.5% obligatory anaerobic. In rumen, 200 species with many subspecies of bacteria are present. There are different kinds of bacteria in the rumen, which aid in fermentation process .
4.2.2. Rumen fibrolytic fungi
Ruminal anaerobic fungi, an emerging group of animal probiotics, account for approximately 8% of the total rumen microbial biomass in ruminants . Rumen fungi have a crucial role in the degradation of fiber material [77–80]. The fungi have an important role in fiber digestion because of the vegetative thallus rhizoids. The rhizoids have a more penetrating capability to plant cell wall as compared to the bacteria and protozoa. Degradation of lignin of the plant cell wall is a main characteristic of rumen fungi [81, 82]. Fungi degraded 37–50% of barley straw. The fungi fibrolytic activity enhanced by hydrogen-utilizing methanogens decreases the cruel effect of hydrogen [76, 83]. Fungi play an active and significant role in fiber digestion of low quality roughages by breaking the beta-1,4 linkages between lignin and hemicelluloses inside the plant cell . Fungi have a positive role in fiber degradation as evidenced by producing a wide array of potential hydrolytic enzymes [79, 85, 86].
4.2.3. Rumen protozoa
In vitro studies have suggested that 19–28% of the total cellulosic activity in fiber digestion can be attributed to protozoa . However, digestion seems to be limited to very susceptible tissue, for instance, mesophyll cells . Studies have demonstrated that defaunation (removal of protozoa) reduces the rate of fiber/cell wall degradation digestion [89, 90]. However, in the absence of protozoa, there is an increased requirement for non-protein nitrogen (NPN) because of an increased bacterial population. A reduction of N may therefore result in the reduction in fiber digestion .
4.3. Mode of action of probiotic yeast in the post-ruminal GIT
The GIT inhabits multifarious microbial diversity that helps in generating impactive response regarding nutritious, health, physiology, and productivity of animals . The existing gut microbiota regulates food safety through shedding of pathogens, interaction with organisms, and resource competition in the GIT . The physiological, anatomical, and immunological status of the host is strongly dependent upon microbiota of GIT which facilitates essential functions to host. GIT microflora aids in the stimulation of immune system that acts as a barrier against infectious pathogens. It also restrains the injurious and pathogenic bacteria gut colonization . The microflora that resides in GIT mostly belongs to
5. Experimental proofs
5.1. Experiment 1: effect of probiotic yeast on the growth performance and fecal biomarkers of dairy heifers
Poor growth performance in growing animals is associated with imbalanced nutrition. The use of probiotic yeast would minimize the expenditure of replacement heifers with optimum growth rate. In our experiment, young animals fed on the diet supplemented with yeast culture gain more weight than non-supplemented animals. In this experimental study, eight dairy heifers (87 ± 5 kg and 6–7 months) were divided into two equal groups of four animals each (control and probiotic) following completely randomized design . During the trial, heifers in control group were offered control diet (NRC recommended diet), while in the probiotic group fed with control diet plus commercial available probiotic yeast (Yea-Sac1026; 5 g/animal) for a period of 120 days. Results reveal that dairy heifers fed on the probiotic feed gained significantly (P < 0.05) higher average weights than dairy heifers fed on control feed (Figures 5 and 6) .
5.2. Experiment 2: development of indigenous probiotic yeast for local breed
From the aforementioned discussion, we found that an important step to establish a breed probiotic strain is that the origin of the isolated strain should be animal based for their better adhesion and colonization in the animal GIT. We hypothesize that, breed-specific probiotic yeast gives better results in terms of milk production. From this line of research, we conduct an experimental study to develop the indigenous probiotic yeast for local breed and to evaluate its effect on the lactating animals. A
5.3. Experiment 3: impact of indigenously isolated
Saccharomyces cerevisiaeprobiotics on milk production and gut microbial species of lactating cows
Nine lactating dairy cattle of mix breed (
We assumed that improved performance is might be due to cellulolytic activity of the
6. Challenges in preparation of suitable probiotics yeast
Traditionally, as ruminates live in different parts of the world, hence, different yeast strains may exhibit different effects upon the ruminal fermentation depending on their location. Therefore, we should identify new yeast strains for getting best results for the rumen fermentation in their own living condition. For getting positive results in the ruminants, probiotic strains should be breed specific. Latest knowledge related to modes of action of probiotic yeast and its beneficial effects on rumen fermentation, may aid in selection of new breed-specific strains which act on specific key target microorganisms (Cellulolytic, hemicellulolytic bacteria and fungi) and areas of rumen fermentation. Inside the rumen fluid, certain probiotic yeast candidate cannot remain active for longer periods of time. On the other hand, probiotic strains viability and stability are the more advanced technological challenges faced by the livestock industry holders. There is a strong interaction between the host animal and microbial population. To overcome these challenges, further empirical studies are needed on the study of probiotic candidates as well as the ruminal gut microbiota activities to enhance the information of the host-specific interactions. Then the goal is to apply the knowledge of ruminal gut health normal microbial species composition in comparison with microbiota present during disease to select the right breed-specific probiotic strain (Figure 10).
7. Conclusions and future research
Probiotic supplemented animal feed has promising effects on the remains to a bright livestock industry future. However, formulating the cost-effective bioactive feed for the dairy animals is remaining as the main challenge faced by the rumen microbiologist. In this regards, search for novel probiotic strains will be the key research and development spot for future livestock markets all over the world. The target oriented applications of specific strains may have huge potential application in treating many chronic disorders in animals. This would lead to have more economical and biological farming. The probiotic strains of same ecological origin may be more compatible with rumen micro-biome fielding maximum outputs. Therefore, the future feed supplementation may be of breed specific. Recently, consumer’s demand about safe and healthy food products has been increased worldwide. Hence, the advantage of using probiotics is not only to enhance the productive performance but also to (contribute to) lower the risk of ruminant GIT carriage of human pathogen and to reduce excretion of polluting outputs such as nitrogen-based compounds and methane. The
The recommendations are outlined as follows:
Isolation of new indigenous bacterial and yeast strains.
Study the probiotic characterization and genetic potential of the probiotic strains.
Complete nutritional profile of the probiotic strains for preparation of probiotic feed.
Application of probiotic strains for more milk and meat production of local breed animals.
Amino acid profile of the milk of dairy animals fed on the probiotic feed.