Effect of Autolyzed Yeast on Performance, Egg Quality, Microbial Population and Intestinal Morphology of Laying Hens

Antibiotics have been routinely supplemented in diets of poultry to maintain their health, reduce stress, and enhance productivity. However, due to the development of resistance of bacteria to antibiotics and the possibility of these pathogens to be zoonotic, the use of various antibiotic products in livestock and poultry production is gradually being banned around the world. With the possibility of further ban in more regions of the world, research interest into alternatives to in-feed antibiotics has increased. One alternative to in-feed antibiotics that has gained research interest for use in poultry is yeast (Saccharomyces cerevisiae). Yeast in both probiotic (live) and prebiotic (dead) forms has been reported to provide several benefits to both healthy of animals, including poultry. The ability of yeast and its components to act as growth promoter could be associated with different mechanisms that it exhibits individually or synergistically. For instance, yeasts have been reported to favor the proliferation of beneficial microbes by serving as substrates for these microbes in the gut. These beneficial microbes, such as Lactobacillus, have been reported to improve gut health as well as exhibit growth-promoting effects in broiler chickens. Specifically, yeast cell wall that is extracted from whole yeast consists mainly of α-mannans and β-1–3-glucans, which are reported to prevent or eliminate bacterial infections. In order to study various levels of autolyzed yeast (Privita) on performance, quality characteristics of egg, cecal microbiology and intestinal histomorphology of laying hens (Hy-line W-36) (64 weeks), an experiment was done with 192 birds for 10 weeks. Treatments were various levels of autolyzed yeast (control, 250 ml/1000l, 500 ml/1000l, and 750 ml/1000l) that conducted in completely randomized design with 8 replications. Egg production (EP) and egg weight (EW) were recorded daily and feed intake (FI) and feed conversion ratio (FCR) were evaluated weekly. Quality characteristics of eggs were evaluated 2 times per period. Iintestinal histomorphology was determined at the end of experiment. At the end of the study, one birds per replicate were killed by cervical dislocation and blood was drawn from the jugular vein. Serum was separated after centrifugation at 4500 g and 4°C for 10 min, and frozen at −20°C until further analysis was conducted for blood biochemical parameters. Serum samples were analysed for concentrations of low-density lipoprotein (LDL), cholesterol, and triglycerides using standard kits (Zist Shimi, Tehran, Iran) with an autoanalyser (Autolab PM 4000; Medical System, Rome, Italy). Then, caecal digesta (1 g) from each bird were aseptically transferred into 9 ml of sterile saline solution and serially diluted. Lactobacilli, Coliforms, and E.Coli were grown on Rogosa–Sharpe agar, MacConkey Agar, and Eosin Methylene Blue Agar, respectively. Plates for Lactobacillus were incubated anaerobically for 48 h at 37 °C. Microbial populations for E. coli and Coliforms were counted after aerobic incubation at 37°C for 24 hours. All samples were plated in duplicate. This study results showed that addition of autolyzed yeast could not change performance parameters. Yolk color was highest at 250 ml/1000l which had a significant difference with 750 ml/1000l (P <0.05). Addition of autolyzes yeast at levels of 500 and 750 ml/1000l significantly increased cecal Lactobacillus and decreased Coliforms of cecum (P < 0.05). Addition of autolyzed yeast at level of 750 ml/1000l significantly decreased cecal Ecoli compared to the other treatments (P < 0.05). The possible reason for the observed response could be the ability of the yeast to maintenance of normal gut microflora as well as preventing the proliferation of pathogenic microbes. This action may partly contribute to increased nutrient digestibility, reduced competition for nutrients, increased nutrient utilization as well as absorption. Villus height of the e duodenum increased in layers fed on 750 ml/1000l compared to the birds fed 250 ml/1000l (P < 0.05). While crypt depth and villus height-to-crypt depth ratios of the duodenum in birds fed 750 ml/1000l compared to the birds 250 ml/1000l decreased and increased, respectively. Crypt depth of jejunum significantly decreased in birds fed highest level of autolyzed yeast compared to the other treatments. Results of this experiment showed that supplementation of autholyzed yeast could not significant change in qualitative and quantitative parameters. But, levels of 500 and 750 ml/1000l autholyzed yeast increased cecal microbial of Lactobacillus and decreased Coliform and the level of 750 ml/1000l decreased Ecoli of cecum and increased villus height and villus height-to-crypt depth ratios of the duodenum.