February 6, 2019 Critical Thinking

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. Studies have disclosed that use of antibiotics in feed to increase chicken performance, however their persistent use are linked to the appearance of resistant bacteria and build-up of residues in animal products. These anomalies have resulted in its prohibition in animal feed by the European Union (EU) in many countries. This stoppage has elicited interest on the use of yeast (Saccharomyces cerevisiae) as a growth enhancement agent in chicken nutrition. Yeast is highly proteineous (44%) but modest in other essential nutrients. Information exist that yeast supplementation enhance gut health and feed efficiency in chickens. This paper is an attempt to pool available data from studies that investigated the impact of yeast 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
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 improves yolk weight and shell thickness and decreased cholesterol content of the yolk (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 the production of smaller egg in layers fed YC supplemented ration contrary to the findings of other authors (Thayer et al. 1975; Liu and Yoon 2002; Tangendjaja and Yoon 2002; Yalc?n et al. 2008a; Yalcin et al. 2010). Nursoy et al. (2004) observed no effect of yeast supplementation on laying performance and feed to gain ratio 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 laying potential of hens fed yeast based rations 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 exist that support the positive action of yeast supplementation on feed conversion ratio (FCR; 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 (0.5 -1.5 g/kg feed) and 1.0 – 4.0 g/kg feed) had similar effect on feed consumption (FC), weight gain (WG) and FCR in laying birds. Additionally, Swain et al. (2011) disclosed similar FC and FCR in laying birds fed control diet (0% yeast) and treatment diets (0.5 – 2.0% yeast). This finding is in concordance with earlier results of Sehu et al. (1997) that up to 15% of inactivated brewer’s yeast can be added in laying hen diets without compromising FC and FCR in quails. Contrary to these results, others have observed that yeast supplementation at 0.2% (Liu and Yoon 2002) and 0.3 – 0.6% (Sanaa et al. 2013) decreased FC in quails. The disparity on the performance of hens fed yeast diets may be linked to the type of yeast used, supplementation rate, feeding duration, genetic up and environmental differences (Mahdavi et al. 2005).
Egg production and quality
Yousefi and Karkoodi (2007) investigated the influence of yeast levels on laying performance and observed comparable laying rates and quality at 0.5, 1.0 and 1.5g/kg feed supplementation levels. This result is in consonance with Yalcin et al. (2008 a, b) who reported comparable egg production data on hens on yeast. Chickens on yeast diets produce heavy egg with enlarged yolk (Swain et al. 2011); improved shell weight and thickness and reduced yolk cholesterol (Yousefi and Karkoodi 2007; Yalcin et al. 2008a; Swain et al. 2011). The prevalence of laying egg with abnormal and broken shells have recorded in chickens following yeast culture supplementation (Park et al. 2001). Other investigators have also observed enhanced egg number, size and yolk cholesterol content in Hyline brown laying aged 22 weeks fed rations containing 0.1-0.4% yeast autolysate (Yalcin et al. 2010). This is in harmony with to the reports of others (Kim et al. 2002; Shivani et al. 2003; Shareef and Al-Dabbagh 2009) who reported that yeast supplementation increases egg production in laying hens. This result is in harmony with Hassanein and Soliman (2010) who reported that yeast enhances egg production and quality (egg white, 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 enhanced egg quality and reduced production rate. 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 hens aged 46-55 weeks lowered egg size. 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).

Skeletal integrity
The issue of skeletal disorders is well reported in both laying 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 provide structural and mechanical support as well as a reservoir for calcium cum phosphorus among others during metabolism (Mutus et al. 2006). Several reports have disclosed that probiotics may improve skeletal quality in poultry. Mutus et al. (2006) have recorded the efficacy of probiotic in improving tibial bone quality in chickens. Plavnik and Scott (1980) reported that addition of 2.5% or 5.0% brewer’s yeast reduces the occurence of leg weakness in meat typed chickens. Enhanced bone mineral metabolism (calcium and phosphorus) in chickens fed diet supplemented with probiotics has been reported (Nahashon et al. 1994). Authors have observed the increased tibia bone quality, percentage ash, tibiotarsal index and phosphorus level that serves as index of bone strength has been witnessed in birds placed yeast supplemented diets (Mutus et al. 2006). Additionally, probiotic supplementation has been noticed to slightly increase the tibia yield stress and modulus of elasticity of birds that determines the strength of the bones.

Haematology and blood chemistry
Blood indices are used as an index of the health status of laying chickens and are influenced by diets. Studies by Yalcin et al. (2008b) have shown that dietary YC supplementation aid in the production of serum protein, lipids and aspect of serum 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 no negative impact 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 lower blood cholesterol (Mahdavi et al. 2005; Yalcin et al., 2008a, 2010, 2014; Hassanein and Soliman 2010) and triglycerides (Yalcin et al. 2014). The observed discrepancy in these studies may be attributed to the variety of the yeast forms or different experiment conditions (etc: environmental stress).

Immune response of laying hens
The gut and the microbes that lives on it plays an important part in protecting 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). Toms and Powrie (2001) and Cotter et al. (2002) have documented the immune stimulating ability of yeast in laying hens. Kabir et al. (2004) and Maziar et al. (2007) investigated the influence of yeast on the body defense system of chickens and reported rise in 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)
Generality of the studies reviewed revealed that introduction of yeast probiotic in laying hen diets improved feed utilization efficiency, egg number/weight, egg (external and internal) quality traits and health status, hence an indication that yeast probiotic can be used in place of antibiotics. Yeast can enhance performance in laying hens via one or combinations of the following modes of action: (i) increasing the number of important microbes in gut through selective removal as well as antagonism (Kabir et al. 2005; Schneitz 2005), (ii) inhibiting the production of toxins by pathogenic microbes (Musa et al. 2009), (iii) Alteration of gut metabolism to aid synthesis and release of endogenous digestive enzymes as opposed to the production bacterial enzyme activity and ammonia (Han et al. 1999; Yoon et al. 2004), (iv) direct nutritional effects or improving feed utilization (Kabir, 2004; Ezema 2007), (v) Stimulation 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 reports on the number of days’ yeast will be included in layer diets and optimum level to included. Therefore, it is suggested that more research be directed at determining the optimal yeast supplementation level that gives optimum egg production and quality be modeled in laying chickens using quadratic function. Furthermore, it is recommended that the inconsistent in the reports of different authors on the efficacy of yeast in enhancing laying performance and quality in layers should be resolved using meta-analysis.

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