Effects of Probiotics on Performance, Intestinal Morphologic and Gut Microbiota Responses in Local and Commercial Strain of Chickens.

Omani chickens represent local breeds of chickens that have long been established in the Sultanate of Oman. They are raised under the traditional system and are well known for their adaptation to harsh environmental conditions. In a series of our previous studies we demonstrated that local Omani chickens exhibited inferior growth performance compared to Cobb500 Broilers when these birds were maintained under closed housing management system. This inferior growth performance was demonstrated to be directly associated with delayed small intestinal villi development during the critical growth period at an early age. Furthermore, using ribosomal DNA based molecular techniques it was shown that the inferior villi development was associated with significantly different microbial populations in the small intestine during this same time period. Alterations in the gut microbiota can have adverse effects on feed efficiency, productivity, and health of chickens. It is well documented in the literature the benefits of probiotics utilization on productive indexes. In addition, administered probiotic in adequate amounts can confer a beneficial physiological effect on the host, improve intestinal structure and above mentioned improve growth performance. The use of probiotics could represent a major opportunity to achieve mutual benefit for both the industry and consumers. To our knowledge, there are no studies however available to evaluate the effects of probiotics on growth performance, intestinal development or microbial populations of various intestinal segments of slow-growing chickens such the local Omani birds. Analysis of chicken gut bacteria has usually been carried out using conventional culture techniques, but these techniques have been found to be inefficient in identifying and classifying certain groups of bacteria. Recent advances in ribosomal DNA based molecular techniques allow identification of different bacterial populations in environmental samples without cultivation. The objective of the current study will be to evaluate the effect of probiotics on growth performance, gut morphology and the biodiversity of the bacterial community in the gastrointestinal tract of two strain of chickens using 16S rDNA- based analysis. This will be the first study to evaluate the effect of dietary probiotics on Omani chicken bacteria populations using molecular techniques with 16S rDNA and the effect of these probiotics on the growth performance and intestinal development.

Omani chickens represent local breeds of chickens that have long been established in the Sultanate of Oman. They are raised under the traditional system and are well known for their adaptation to harsh environmental conditions. In a series of our previous studies we demonstrated that local Omani chickens exhibited inferior growth performance compared to Cobb500 Broilers when these birds were maintained under closed housing management system. This inferior growth performance was demonstrated to be directly associated with delayed small intestinal villi development during the critical growth period at an early age. Furthermore, using ribosomal DNA based molecular techniques it was shown that the inferior villi development was associated with significantly different microbial populations in the small intestine during this same time period. Alterations in the gut microbiota can have adverse effects on feed efficiency, productivity, and health of chickens. It is well documented in the literature the benefits of probiotics utilization on productive indexes. In addition, administered probiotic in adequate amounts can confer a beneficial physiological effect on the host, improve intestinal structure and above mentioned improve growth performance. The use of probiotics could represent a major opportunity to achieve mutual benefit for both the industry and consumers. To our knowledge, there are no studies however available to evaluate the effects of probiotics on growth performance, intestinal development or microbial populations of various intestinal segments of slow-growing chickens such the local Omani birds. Analysis of chicken gut bacteria has usually been carried out using conventional culture techniques, but these techniques have been found to be inefficient in identifying and classifying certain groups of bacteria. Recent advances in ribosomal DNA based molecular techniques allow identification of different bacterial populations in environmental samples without cultivation. The objective of the current study will be to evaluate the effect of probiotics on growth performance, gut morphology and the biodiversity of the bacterial community in the gastrointestinal tract of two strain of chickens using 16S rDNA- based analysis. This will be the first study to evaluate the effect of dietary probiotics on Omani chicken bacteria populations using molecular techniques with 16S rDNA and the effect of these probiotics on the growth performance and intestinal development.

Chicken intestinal tract is composed of duodenum, jejunum, ileum, cecum and colon, which are inhibited by various microbiota and different intestinal regions are distinguished from each other in the morphology and function (Xiao et al., 2017). The chicken gastrointestinal tract (GI) has a bacterial population present soon after hatching (Lumpkins et al., 2010). Chicken intestinal microbiota start to colonize between 2 and 4 days after hatching and are usually established in the small intestine by approximately 2 weeks post hatching, but might take longer time up to 30 days to be fully developed in the cecum (Amit-Romach et al., 2004). However, the composition of the intestinal microflora continues to change over time under the influence of different factors, such as bird age and dietary factors (Mackie et al., 1999; Xu et al., 2003). There is also significant diversity in bacterial populations among different parts of the digestive tract of the birds (Al-Marzooqi et al., 2019; Richards et al., 2005). Each region of the GI tract develops its own unique microbial profile, and the composition of the microflora becomes more complex and changes in relation to the age of the chickens, different dietary ingredients (Gong et al., 2002a,b; Van der Wielen et al., 2002; Amit-Romach et al., 2004), breed and geographic location (Al-Marzooqi et al., 2019; Apajalahti et al., 2001; Lu et al., 2003;). The development of the intestinal bacteria of different genetic lines of chickens has become a recent point of interest (Lumpkins et al., 2010). However, little is known about how the bacterial community varies among these different genetic strains of chickens, especially those with various growth rates such as the indigenous chickens. It is generally known that the diverse gut microbiota play an important role in host metabolism, nutrient digestion, growth performance and health of the host (Thacker, 2013). In poultry, managing gut health is important to ensure the best bird performance and health as unbalanced microbiota can prompt inflammation or other gut-related disorders (Tellez and Latorre, 2017). Stabilizing or restoring microbiota by the use of probiotics, for example, is well described by numerous published studies (Fuller 1989; Rolfe 2000; Choi et al., 2015). The main postulated health benefits associated with probiotics have been shown to reduce disease risk, possibly through a reduction in the proliferation of pathogenic species, maintaining microbiota balance in the gut and increasing resistance to infection (RamirezChavarin et al., 2013; Smug et al., 2014). In addition, probiotic application has been reported in the poultry industry with an emphasis on their influence on the growth performance of chickens and their carcass compositions (Sarangi et al., 2016). To our knowledge there are no studies that have comprehensively investigated the effects of probiotics on the production parameters or on the diversity of the gut microbiota of local Omani chickens. Although considerable amount of literature is available on genetic parameters of growth traits of commercial chicken strains, but same information may not be relevant in slow-growing native chickens. The improvement of local chicken?s productivity will be highly valuable in the relief of the socio-economic and nutritional status of the farmers. With the development of animal husbandry in Oman, local chicken production is becoming more widespread. To ensure effective production of local chicken it is critical to assess their growth performance and the diversity and succession of the intestinal bacterial community in different segments of the gastrointestinal tract. Availability of such information might form the basis for improving the productivity of local chicken production. Furthermore, from the literature it is apparent that considerable variation exists in the production traits of native chicken breeds and more investigations are required to establish baseline values for production parameters and characterize their general performance. Advances in ribosomal DNA-based molecular techniques have made it possible to obtain new information by identifying different bacterial populations in intestinal contents and mucosal samples as compared with routine culturing methods. These techniques are also helpful for monitoring the effects of dietary factors and other variables on the microbial communities of the chicken intestine under different management conditions (Apajalahti et al., 1998, 2001; Gong et al., 2002b; Knarreborg et al., 2002; Van der Wielen et al., 2002; Amit-Romach et al., 2004). Several studies have shown that sequence identification is useful for slow-growing, unusual, and fastidious bacteria, as well as for bacteria that are poorly differentiated by conventional methods (Patel, 2001). In addition, recent advances in ribosomal DNA based molecular technique make it possible to identify different bacterial populations in environmental samples without cultivation (Harmsen et al., 2000). There is great importance in examining and monitoring the intestinal microflora because many bacterial species with pathogenicity toward humans have been found in the gastrointestinal tract of chickens and can thus be introduced into the food chain (Reeves et al., 1989; Davies and Wray, 1996; Brandt et al., 1999; Moreno et al., 2001). An understanding of the development of the normal bacterial community will permit to identify disruption in the flora community and analyze the effects of food birds management changes. This information may make it possible to manipulate the intestinal flora with the intention of enhancing intestinal health and feed conversion as many factors can affect the composition of the avian bacterial community, such as diet Knarreborg et al., (2002), age (Knarreborg et al., 2002; Van der Wielen et al., 2002, Zhu et al., 2002) and various environments (Waite and Taylor, 2014).