Evaluation of Liquid Organic Acids on the Performance, Chyme pH, Nutrient Utilization, and Gut Microbiota in Broilers under High Stocking Density

SIMPLE SUMMARY: Organic acids (OAs) are proposed as suitable alternatives in animal production. The released protons of OAs can reduce the pH in the gastrointestinal tract, then, nutrient digestion is stimulated by boosting the secretion of endogenous enzymes. In addition, lower intestinal pH suppresses pathogenic bacterial growth and encourages beneficial bacterial growth. In the starter phase, broilers are young, and their digestive tract is not well developed; thus, the first purpose of this study is to evaluate the efficacy of liquid OAs on the growth performance, serum metabolism lipid profiles, chyme pH, and duodenal enzymes activity in broilers during the starter phase. In addition, since a high stocking density (HSD) usually occurs in grower broilers and can lead to some disadvantages, whether supplemental OAs could alleviate the HSD stress condition in grower broilers is the second study aim of this study. Hence, the objective of the current study was to investigate whether the supplementation of liquid OAs in an entire period could alleviate the grower broilers’ stress status under an HSD. We found that OAs decreased the chyme pH in the upper digestive tracts and increased the activity of digestive enzymes in broilers during starter and grower phases. In addition, an HSD decreased the growth performance, while OAs showed no efficacy in the growth performance but improved the nutrient utilization in grower broilers. The alterations of gut microbiota were observed in grower broilers supplemented with OAs. In addition, the mechanisms of OAs in regulating the lipid metabolism and gut bacteria need further investigations. ABSTRACT: This study aimed to evaluate the efficacy of organic acids (OAs) in starter broilers and to investigate whether supplemental OAs could alleviate the high stocking density (HSD) stress condition in grower broilers. A total of 408 1-day-old Arbor Acres broilers were assigned into two groups without or with liquid OAs in the starter phase. In the grower phase, each group in the starter phase was divided into a normal stocking density and an HSD. The OA dose was 0.16% at the starter and grower phases. The results showed that at the starter phase, OAs decreased the chyme pH in gizzard and duodenum and increased the activities of chymotrypsin and α-amylase in the duodenal chyme (p < 0.05). In the grower phase, an HSD decreased the growth performance and the ether extract digestibility (p < 0.01). The supplementation of OAs decreased the chyme pH in the gizzard, proventriculus, and duodenum and increased the lipase and α-amylase activities (p < 0.05). The supplemental OAs increased the dry matter and total phosphorous digestibility and the contents of acetic acids, butyric acids, isovaleric acids, and valeric acids (p < 0.05). For cecal microbial compositions at the genus level, an HSD decreased the relative abundance of Blautia, Norank_f__norank_o__RF39, and Alistipes, while supplemental OAs increased the relative abundance of Norank_f__norank_o__RF39 (p < 0.05). In conclusion, although there were no interaction effects between OAs and stocking densities in the present study, it was clear that the supplementation of OAs has beneficial effects on the chyme pH, enzymes activities, and nutrient digestibility in broilers, while an HSD existed adverse effects on the growth performance, nutrient digestibility, and gut microbiota balance in grower broilers.