Dietary Chitooligosaccharide Inclusion as an Alternative to Antibiotics Improves Intestinal Morphology, Barrier Function, Antioxidant Capacity, and Immunity of Broilers at Early Age

SIMPLE SUMMARY: At early an age, broilers are susceptible to exterior stressors and therefore have a higher disease incidence rate. Antibiotic growth promoters have been forbidden in animal production by the European Union and other countries since their usage has caused potentially adverse effects such as antibiotic residues in livestock, environmental pollution, and the generation of drug-resistant bacteria. The search for safe and environmentally friendly alternatives to antibiotics to prevent disease and promote growth has become necessary in poultry production. Chitooligosaccharide (COS), a natural alkaline polymer of glucosamine with a number of bioactive groups, is easily obtained by chemical and enzymatic hydrolysis of chitosan, which is the second most abundant carbohydrate polymer in nature. Our results indicated that dietary supplementation with chitooligosaccharide, at a dosage of 30 mg/kg, enhanced the feed conversion ratio, benefited the intestinal morphology and barrier function, and improved antioxidant capacity and immunity in broilers at 21 days of age. These effects were similar with those observed as a result of chlortetracycline inclusion. Therefore, dietary COS supplementation can be used as a potential alternative to antibiotics in broilers. ABSTRACT: This study aimed to investigate the effects of chitooligosaccharide (COS) inclusion as an alternative to antibiotics on growth performance, intestinal morphology, barrier function, antioxidant capacity, and immunity in broilers. In total, 144 one-day-old Arbor Acres broiler chicks were randomly assigned into 3 groups and fed a basal diet free from antibiotics (control group) or the same basal diet further supplemented with either chlortetracycline (antibiotic group) or COS, for 21 days. Compared with the control group, inclusion of COS reduced the feed to gain ratio, the jejunal crypt depth, the plasma diamine oxidase activity, and the endotoxin concentration, as well as jejunal and ileal malondialdehyde contents, whereas increased duodenal villus height, duodenal and jejunal ratio of villus height to crypt depth, intestinal immunoglobulin G, and jejunal immunoglobulin M (IgM) contents were observed, with the values of these parameters being similar or better to that of the antibiotic group. Additionally, supplementation with COS enhanced the superoxide dismutase activity and IgM content of the duodenum and up-regulated the mRNA level of claudin three in the jejunum and ileum, when compared with the control and antibiotic groups. In conclusion, dietary COS inclusion (30 mg/kg), as an alternative to antibiotics, exerts beneficial effects on growth performance, intestinal morphology, barrier function, antioxidant capacity, and immunity in broilers.