Evaluation of soybean meal bioactive peptides and Spirulina powder as antibiotic alternatives on growth performance, physiological responses, and intestinal gene expression in broilers.

This study aimed to evaluate the effects of dietary soybean-derived bioactive peptides (SBP) and Spirulina powder (SP) as antibiotic alternatives on performance, amino acid digestibility, antioxidant status, and intestinal health-related gene expression in broiler chickens. A total of 250 male and female Ross 308 one-day-old chicks were used in a completely randomized design with 5 treatments, 5 replicates, and 10 chicks per replicate. The experimental treatments included: (1) a control diet consisting of the standard basal diet without any additive (CON); (2) a basal diet supplemented with avilamycin at 100 g/ton of feed (ANT); (3) a basal diet supplemented with SBP at 2 g/kg of feed (SBP); (4) a basal diet supplemented with SP at 2 g/kg of feed (SP); and (5) a basal diet supplemented with a combination of 1 g/kg SBP and 1 g/kg SP (SBP-SP). Body weight gain and feed intake during the starter and grower phases, as well as over the entire experimental period (1-42 d), was significantly greater in birds fed the SBP-SP diet compared with the CON and SP groups (P < 0.05). Broilers fed the SBP-SP, ANT, and SBP diets exhibited higher apparent ileal digestibility of Methionine, Isoleucine, Threonine, Aspartic acid and Glutamic acid compared with those fed the CON and SP diets (P < 0.05). Dietary inclusion of SBP-SP and ANT led to a substantial increase in both villus height, villus surface area, and the villus height to crypt depth ratio when compared to the CON group. Dietary supplementation with SP and SBP-SP significantly boosted the IBV antibody titers at both 21 d (P = 0.006) and 42 d (P = 0.017) compared to the CON, ANT, and SBP groups. The relative weight of the Bursa of Fabricius and Thymus was markedly increased in birds supplemented with SBP-SP and SP compared to those in the CON and SBP groups (P = 0.015). Broilers receiving the SBP-SP and SP treatments exhibited significantly higher levels of TAC, SOD, GPx, and CAT compared with the CON and ANT groups. The mRNA levels of IL-1β and TNF-α were markedly downregulated in birds receiving the SBP-SP diet compared to all other experimental groups (P < 0.05). The expression of ZO-1, MUC2, SLC15A1, SLC6A19 and SLC7A1 was significantly upregulated in the SBP-SP group compared to the CON group (P < 0.05). Collectively, these findings indicate that the combined use of SBP and SP exerts synergistic effects on digestive efficiency, intestinal function, and physiological status, suggesting that this combination may serve as a promising natural alternative to antibiotic growth promoters in broiler nutrition.