YEAST (SACCHAROMYCES CEREVISIAE) AS PROBIOTICS OF CHOICE
FOR LAYING CHICKENS
I.P. Ogbuewu and C.A. Mbajiorgu
Department of Agriculture and Animal Health, University of South Africa,
Florida Science Campus, Johannesburg, South Africa
Corresponding author’s e-mail: [email protected]
Antibiotics is included in minute level in chicken ration to promote productivity and physiological well-being. But studies have revealed that incorporation of antibiotics in feed to increase chicken performance causes the emergence of resistant bacteria. Their use in poultry feed lead to accumulation of significant amount of residues in animal products. These normally have led to the stoppage on the use of antibiotics in animal feed by the European Union (EU) in several parts of the world. This stoppage has elicited interest on the use of Yeast (Saccharomyces cerevisiae) as a replacement for antibiotics in chicken nutrition. Yeast is abundant in protein (44%) and moderate in other essential nutrients. Information exist that yeast supplementation enhance gut health and feed efficiency in chickens. This paper is an attempt to document all the information on the effect of yeast supplementation on health status, egg production and egg quality in laying chickens as to identify knowledge gap for future research.
Keywords: Probiotics, yeast supplementation, chickens, laying performance, egg quality
Introduction
The prolonged use of a small dose of antibiotics in livestock and poultry feed has implicated in the host and cross drug resistance (Jones and Ricke 2003). In view of the public health implication of using sub-dose of therapeutic antibiotics in feed calls the search for alternative natural growth stimulants such as yeast (Patterson and Burkholder 2003; Khan and Naz 2013). Studies by Reed and Naodawithana (1999) and McDonald et al. (1988) have shown that yeast is rich in protein and moderate in B-vitamins and trace mineral elements (Table 1). In addition, studies (Haiman and Frank 1994; Yalcin et al. 2014) showed that yeast contains all the essential amino acids needed by chickens for growth and egg production (Table 2). Furthermore, Samanta and Mondal (1988) revealed that dried yeast cell is very high in methionine (2.46%), threonine (3.98%) and tryptophan (0.77%). Results of proximate analysis of yeast showed dried yeast had 95.7% dry matter (DM), 10.7% ash, 48.7% protein, 0.55% crude fat, 0.5% fibre, 35.5% carbohydrates, 5.50% phosphorus, 2.0% potassium and 0.03% chloride (Hamad, 1986). Studies have revealed that S. cerevisiae stimulates appetite (Nahashon et al. 1992) and improve immunity (Toms and Powrie, 2001; Cotter et al., 2002) on layers. In the gut, yeast has been established to reduce the population of pathogenic micro-organisms and decrease pH (Fuller, 1989). Several investigators reported that feeding yeast mannan oligosaccharide (MOS) results to improve immune response in chickens (Raju and Devegowda, 2002; Cotter et al., 2002; Shashidhara and Devegowda 2003) while, yeast culture (YC) inclusion at 0.5 – 1.5 g/kg diet increases shell thickness, yolk weight and reduced egg yolk cholesterol content chickens (Yousefi and Karkoodi 2007). Similar results were obtained by other scientists who reported that YC supplementation increases egg production and weight (Thayer et al. 1975; Liu and Yoon 2002; Tangendjaja and Yoon 2002Yalc?n et al., 2008a; Yalcin et al. 2010), improve feed efficiency (Liu and Yoon, 2002; Tangendjaja and Yoon 2002; Dizaji and Pirmohammadi 2009) and reduced egg yolk cholesterol (Yalcin et al. 2008a) and serum cholesterol cum triglycerides concentration (Jin et al. 1998; Yalcin et al. 2010). Dizaji and Pirmohammadi (2009) noticed reduced egg weights on layers on YC supplementation contrary to the results of other authors (Thayer et al. 1975; Liu and Yoon 2002; Tangendjaja and Yoon 2002; Yalc?n et al. 2008a; Yalcin et al. 2010), while Nursoy et al. (2004) observed no statistical effect of yeast supplementation on egg production, egg weight, and feed efficiency in laying chickens. The growing benefits of S. cerevisiae on egg production in chickens are linked to either its direct nutritional effect or its potential to reduce the population of pathogenic microbes in the gut and strengthen the host’s natural body defense (Fuller 1977; Fuller 2001).

The objective of this review was to aggregate all the available information on egg production performance of laying hens fed yeast diets in a single document for easy access by researchers and research end-users as well as to identify knowledge gap for future research.
Table 1 Proximate biochemical and mineral composition of yeast cell wall
Parameters Yalcin et al. (2014) Osman (2010) %
Proximate Dry matter (g/kg) 935.5 98.20%
ME (MJ/kg) 5.17 3276.26 (Kcal/kg)
Crude protein (g/kg) 227.2 38.90
Ether extract (g/kg) 37.4 1.60
Crude fibre (g/kg) 4.3 0.4
Crude ash (g/kg) 64.0 4.87%
Minerals (mg/kg) Calcium 7390 1.0
Phosphorus 5906 0.05
Magnesium 1230 0.4
Sodium 15750 –
Potassium 5829 3.84
Zinc 130 –
Manganese 36 –
Table 2 Amino acid profiles of yeast cell wall
Parameters Free amino acids (g/kg) Total amino acids (g/kg)
Aspartic acid 0.05 16.10
Glutamic acid 1.54 24.40
Serine 0.07 7.04
Histidine 0.02 4.76
Glycine 0.15 11.18
Threonine 0.02 5.31
Arginine 0.07 6.22
Alanine 0.67 13.01
Tyrosine 0.06 7.77
Valine 0.05 12.32
Methionine 0.01 3.96
Phenylalanine 0.06 12.96
Isoleucine 0.02 11.72
Ornithine <0.03 5.76
Leucine 0.03 19.04
lysine 0.02 15.69
Hydroxyproline0.3 8.05
Proline 1.00 14.91
Adapted from Yalcin et al. (2014)
Feed intake and nutrient utilization
Studies abound that show the benefit of yeast supplementation on feed conversion ratio (kg feed/kg egg) in layers (Maziar et al. 2007; Songsak et al. 2009; Hassanein and Soliman 2010), weight gain (Sharmah et al. 2001; Yalcin et al. 2008a), energy utilization (Bradley and Savag 1995) and digestion coefficient of crude protein (Soliman 2003). In contrast, Yousefi and Karkoodi (2007) and Yalcin et al. (2014), respectively found that yeast supplementation (0.5 -1.5 g/kg feed) and 1.0 – 4.0 g/kg feed) had similar effect on feed intake, body weight and feed conversion ratio (FCR) in laying birds. Additionally, Swain et al. (2011) showed that of yeast (0.5 – 2.0%) did not affect feed intake in laying birds which also confirmed the earlier statement of Sehu et al. (1997) that up to 15% of inactivated brewer’s yeast can be added in laying hen diets without adverse effect on feed intake and FCR in quails. Contrary to these results, others have observed noticed that yeast supplementation at 0.2% (Liu and Yoon (2002) and 0.3 -0.6% (Sanaa et al. 2013) reduced feed intake in quails. The disparity on the response of laying birds to varying levels of yeast diets may be linked to yeast type, supplementation rate, duration of feeding, genetic up and environmental differences (Mahdavi et al. 2005).
Egg production and quality
Yousefi and Karkoodi (2007) investigated the dose-related effect of yeast on laying performance traits and observed similar egg production indices and quality at 0.05%, 0.1%, and 0.15% supplementation levels. This result is in consonance with Yalcin et al. (2008 a, b) who reported similar egg production data in birds on yeast. Chickens fed probiotic yeast supplemented diets have been noticed to produce large egg and yolk (Swain et al. 2011); heavier shell weight, increase shell thickness and reduced yolk cholesterol (Yousefi and Karkoodi 2007; Yalcin et al. 2008a; Swain et al. 2011). The incidences of laying soft shell and broken eggs have recorded in chickens following yeast culture supplementation (Park et al. 2001). Other investigators have also observed increased egg production and egg weight and decreased the concentration of egg yolk in Hyline brown laying aged 22 weeks fed diets containing 0.1-0.4% yeast autolysate (Yalcin et al. 2010). This is similar to the findings of others (Kim et al. 2002; Shivani et al. 2003; Shareef and Al-Dabbagh 2009) who reported that yeast supplementation improves egg production in laying hens. This result is in harmony with Hassanein and Soliman (2010) who reported that yeast improves egg production and quality (egg albumen, egg yolk, and eggshell thickness) in white leghorn layers fed live yeast culture at 0.4% and 0.8%. Similar findings were obtained in egg typed chicken fed yeast diet (Sharmah et al. (2001). Sanaa (2013) evaluated the dose-related effect of yeast supplementation on layers and observed that the group in 0.3% yeast had 4.67% increase in shell thickness and 2.59% reduction in albumen weight. Similarly, Nursoy et al. (2004) recorded an increase in eggshell thickness in laying birds fed S. cerevisiae based diet at 0.8%, while Songsak et al. (2009) observed that addition of cassava yeast probiotic at 1×106, 1×107 and 1×108 microorganism/kg in layer diet for 8 weeks increased egg weight and eggshell thickness and reduced hen day production. However, the observed increase in eggshell thickness of birds fed yeast diet may be due to the ability to enhance calcium (Bradley and Savage 1995) and phosphorus availability (Reed and Naodawithana 1999). In contrast, Sanaa (2013) reported that yeast supplementation at 0.3 and 0.6% in layer diets reduced hen-day production and egg number. Similar results were also recorded by Dizaji and Pirmohammadi (2009) who found that adding yeast inclusion at 0, 200, 300, 400g/ton of diet) for 10 weeks in laying hens aged 46-55 weeks reduced egg weight. The discrepant variations in these studies may be fully explained but can be partly attributed to the strains of birds used, yeast type as well as the rearing environment (Mahdavi et al. 2005).

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Skeletal integrity
The problems of skeletal disorders have been well reported in both egg and meat typed chickens reared in a confined setting due to their fast growth and high egg production ability. In both in mammals and avian, bones have been well reported to provide structural and mechanical support as well as a storehouse for calcium and phosphorus among others during metabolism (Mutus et al. 2006). Several investigators suggest that probiotics may enhance bone strength and development in poultry. Mutus et al. (2006) reported the positive effect of probiotic supplementation on properties of the tibial bone in chickens. Plavnik and Scott (1980) reported that addition of 2.5% or 5.0% brewer’s yeast reduces the incidences of leg weakness in meat typed chickens. Better calcium and phosphorus retention and increased bone mineral deposit in the skeleton of chickens fed diet supplemented with probiotics has been reported (Nahashon et al. 1994). Authors have reported the increased thickness of the medial and lateral wall of the tibia, percentage ash, tibiotarsal index and phosphorus content, which are used as an index of bone strength has been reported in birds placed yeast supplemented diets (Mutus et al. 2006). Additionally, probiotic supplementation has been observed to slightly improve the tibia yield stress and modulus of elasticity of birds, which are used to the rigidity of the bones.

Haematology and blood chemistry
Blood indices are used as an index of the health status of laying birds and they are influenced by dietary factors. Studies by Yalcin et al. (2008b) have found that dietary YC supplementation supports serum protein, lipids and aspect of liver enzymes in layers. Similar findings were also reported by Sanaa (2013) and Yalcin et al. (2014) who reported that addition of 0.3% and 0.6% dried yeast in chickens support the production of serum protein, lipids, and aspect of liver enzymes. In similar studies, Wakwak et al. (2003) and Maziar et al. (2007) observed no significant effect of yeast on serum proteins and cholesterol, respectively while inclusion of 0.2% of YC in laying hens ration containing either soybean meal or sunflower meal had comparable serum aspartate transaminase (AST) and alanine transaminase (ALT) (Yalcin et al. 2008a), and this implies that there was no deamination of amino acids. This result corroborated Hewida et al. (2011), who reported that YC had a similar influence on serum proteins and serum creatinine. Others studies have noticed the nonsignificant effect of yeast on blood cholesterol in laying hens (Stanley et al. 2004; Bageridizaj et al. 2006; Pinar et al. 2013). A similar study in quails fed with 1 or 2% yeast supplementation, Ghally and Abd El-Latif (2007) recorded improved blood constituents (serum proteins, AST and ALT). Contrary to these findings, some investigators have shown that addition of yeast on hen diets significantly reduce the concentrations of serum cholesterol (Mahdavi et al. 2005; Yalcin et al., 2008a, 2010, 2014; Hassanein and Soliman 2010) and serum triglycerides (Yalcin et al. 2014). The observed variations in these studies may be attributed to the variety of the yeast forms or different experiment conditions (etc: environmental stress).

Immune status of laying chickens
The gut and its inhabiting microorganisms play a vital role in shaping the body defense system in poultry (Diarra et al. 2011). Yeast cell wall products (chitin, mannan, and glucan) are known to stimulate the gut defense systems, increase immunoglobulin levels (Abaza et al. 2008), and white blood cell count (Abdollahi et al. 2002). The immune (Toms and Powrie, 2001; Cotter et al., 2002) stimulation potential of yeast products in breeders and laying hens have been reported. Kabir et al. (2004) and Maziar et al. (2007) investigated the influence of yeast on the body defense system of chickens and observed increased antibody production (p<0.01) in treated birds compared to the control birds. Likewise, Haghighi et al. (2006) reported increased serum and intestinal natural antibodies to several foreign antigens in chickens. Ezema (2012) reported a significant increase in absolute lymphocyte count in experimental birds fed S. cerevisiae supplemented diets compared to the control birds. MOS has been documented to improve antibody responses in broiler and layers (Raju and Devegowda 2002; Cotter et al., 2002). In contrast to the findings of others (Raju and Devegowda 2002; Cotter et al., 2002), Pinar et al. (2013) have reported non significant increase in weekly serum antibody titer in brown lay hens (aged 22 weeks) fed inactivated yeast supplemented diets for 14 days (Figure 1) whereas, Yalcin et al. (2014) obtained a significantly higher antibody titer in laying brown hens (aged 29 weeks) fed yeast cell wall based diets for 26 weeks compared to the control group (Figure 2). The observed variations in the two studies (Pinar et al. 2013; Yalcin et al. 2014) may be attributed to the duration of feedings, yeast form and age differences.

Figure 1: Serum antibody titer of laying hens to yeast diets

Figure 2: Serum antibody titer of laying hens to yeast diets
a, bBars with different superscripts differed significantly (p<0.05)
Conclusion
Majority of the primary studies reviewed showed that addition of yeast probiotic in laying hen diets improved feed utilization efficiency, egg number/weight, egg (external and internal) quality traits and health status, thus an indication that yeast probiotic can serve as an alternative to in-feed antibiotics. Yeast may have achieved via one or combinations of the following modes of action: (i) increasing the number of good microbes in gut through selective exclusion and antagonism (Kabir et al. 2005; Schneitz 2005), (ii) inhibiting the production of toxins by pathogenic microbes (Musa et al. 2009), (iii) Alteration of gut metabolic processes in favour of production and release of endogenous digestive enzymes as against the production bacterial enzyme activity and ammonia (Han et al. 1999; Yoon et al. 2004), (iv) direct nutritional effects or improving feed intake, digestion and nutrient utilization (Kabir, 2004; Ezema 2007), (v) Activation of gut defense system (Haghighi et al. 2006; Apata 2008), and (vi) Decreasing gut pH via increased volatile fatty acids production (Chichlowski et al. 2007; Choudhari et al. 2008). Furthermore, there were no consensus results on the duration of feeding and optimum inclusion level with the best production response. Therefore, it is suggested that future research should be directed at determining the dose-related response on egg production and quality to dietary supplementation be modeled in laying chicken using quadratic equation quadratic.

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