The gastrointestinal microbiome and its association with the control of pathogens in broiler chicken production: A review

Abstract

The microbiome of the broiler chicken gastrointestinal tract (GIT) has been extensively studied, and it has been amply demonstrated that it plays an important role in the health of the host, as it has a positive impact on the immune system, the physiology of the GIT, and productivity. Also, the microbiota is involved in reducing and preventing colonization by enteric pathogens through the process of competitive exclusion and the production of bacteriostatic and bactericidal substances. The taxonomic composition of the microbiota is affected by different factors, such as the organ, the age of the animal, diet and the use of antimicrobials.Different kinds of additives that regulate the microbial community in feed include probiotics (live microorganisms that when administered in adequate amounts confer a health benefit on the host), prebiotics (ingredients that stimulate increased beneficial microbial activity in the digestive system in order to improve the health of the host) and phytobiotics (primary or secondary components of plants that contain bioactive compounds that exert a positive effect on the growth and health of animals). Phages may potentially provide an integrated solution to modulate the intestinal microbiome of chicken intestines, as they reduce specific pathogenic microbial populations, permitting the proliferation of beneficial microbiota. Studies have shown that the use of cocktails of phages, especially in high concentrations and with short lapses of time between exposure to the bacteria and treatment with phages, optimize the reduction of Salmonella in chickens. Each of these technologies has demonstrable positive effects on the health of the host and the reduction of the pathogen load in controlled assays.This paper presents a comprehensive summary of the role of the microbiota in the broiler chicken gastrointestinal tract, and discusses the usefulness of different strategies for its modulation to control pathogens, with a particular emphasis on bacteriophages.

Figure 1.

Gastrointestinal tract in chickens and function. The beak gathers food; the bifurcated tongue, located in the posterior part of the beak, is used to drink and to moisten the material that has been taken up. Subsequently, the food passes to the esophagus, which transports the food and water to the crop. The esophagus contains mucus glands that help to lubricate the passage of the food to the crop where it is stored temporarily. In its passage through the esophagus, the food is softened and undergoes pre-digestion by enzymes such as ptyalin, present in saliva, and enzymes from other organs, such as amylase-types from the duodenum and the proventriculus. The crop fills up when the chicken has eaten enough, and the food passes slowly to the proventriculus, or glandular stomach. Here, foodstuffs are bathed in gastric juices, hydrochloric acid, and digestive enzymes, beginning the process of nutrient breakdown and the construction of the food bolus, which then passes to the gizzard. The enzyme pepsin, which performs its proteolytic activities in the proventriculus, is also produced in the gizzard, as acid levels in the stomach are below the optimum levels required for it to function. The gizzard, also known as the masticatory organ in chickens, accumulates insoluble grains, which are ground by frequent and repeated contractions that exert enormous pressure, breaking the grains down into small particles and mixing them with juices from the proventriculus. From the gizzard, the food passes to the small intestine, an organ that is distinguished histologically by the presence of villi, which complete the digestion of proteins through the secretion of intestinal juices and digestive enzymes such as aminopeptidase, amylase, maltase, and invertase; another function is to absorb the nutrients in the digested foodstuffs so that they can enter the bloodstream; finally, the small intestine provides peristaltic action that passes undigested materials to the ceca. The small intestine has 3 sections: the duodenum, the jejunum, and the ileum. The pancreas is the organ that secretes juices enriched with amylases, trypsin, lipases and carboxypeptidases. The liver secretes bile into the duodenum, which helps break down fats; the bile, though produced in the liver, is stored in the gallbladder. The ileum opens into the ceca, a pair of tubes where undigested foodstuffs are fermented, and which is emptied every 24 h. The water and the foodstuffs that are not digested in the small intestine, such as non-starch polysaccharides, are absorbed in the large intestine, a section of the digestive tract that leads from the junction with the ceca, through the colon, and ends in the external opening of the cloaca (Noy and Sklan, ; Uni et al., ; Rebollar Serrano and Serrano, 2002).