Effects of Probiotics as Antibiotics Substitutes on Growth Performance, Serum Biochemical Parameters, Intestinal Morphology, and Barrier Function of Broilers

SIMPLE SUMMARY: The abuse of antibiotics in animals feed may cause antibiotic-resistant microbes and antibiotic residue in animal products. Probiotics (PB) have been used in the feed industry for several decades due to their beneficial effects on immunity and the growth of livestock and poultry. However, the efficiency of PB on animals varies due to the types and dose of PB. Therefore, investigating the effects of PB (Bacillus subtilis, Bacillus licheniformis, and Saccharomyces cerevisiae) as an antibiotic substitute on growth performance and intestinal health status in broilers is valuable and meaningful. ABSTRACT: The aim of this study was to investigate the effects of the combination of probiotics replacing antibiotics on growth performance, serum biochemical parameters, intestinal morphology, and expression of tight junction proteins in intestinal mucosa of broilers. A total of 168 Arbor Acres broilers (45.04 ± 0.92 g) were randomly divided into three treatments, with seven replicates per treatment, and eight broilers per replicate. The experiment included phases 1 (d 0 to 21) and 2 (d 21 to 42). The dietary treatments contained a corn soybean meal-based diet (control group; CON); an antibiotic group (basal diet + 75 mg/kg chlortetracycline; CTC), and a probiotics group (basal diet + probiotics (500 mg/kg in phase 1 and 300 mg/kg in phase 2; Bacillus subtilis 5 × 10(9) CFU/g, Bacillus licheniformis 2.5 × 10(10) CFU/g and Saccharomyces cerevisiae 1 × 10(9) CFU/g; PB). The results showed broilers fed PB had improved (p < 0.05) feed conversion ratio (FCR) in phase 1 and increased (p < 0.05) average daily gain (ADG) in phase 2, as well as improved (p < 0.05) ADG and FCR overall (d 0 to 42). The apparent total tract digestibility (ATTD) of dry matter, organic matter, gross energy, and crude protein was increased (p < 0.05) in broilers fed PB, while the ATTD of dry matter and organic matter was enhanced in broilers fed CTC compared with CON. Broilers fed PB showed increased (p < 0.05) serum total antioxidant capacity concentrations and tended to have higher (p = 0.06) level of serum immunoglobulin M in phase 1 compared with CON. These broilers also had increased (p < 0.05) level of serum immunoglobulin A in phase 2 in comparison with CON and CTC. Moreover, broilers fed CTC and PB showed increased (p = 0.05) villus height to crypt depth ratio in duodenum, as well as higher (p < 0.05) mRNA expression of zonula occludens-1 in jejunum compared with CON. In conclusion, dietary supplementation with PB as chlortetracycline substitute could improve the growth performance, nutrient digestibility, serum antioxidant capacity, jejunal mucosal barrier function, and intestinal morphology of broilers.