Abstract
Lysozyme is often used as a feed additive to act as an antibacterial protein that boosts the immune system of livestock and poultry while protecting against pathogens. To investigate the effects of recombinant human lysozyme (rhLYZ) from Pichia pastoris and chlortetracycline on broiler chicken's production performance, antioxidant characteristics, and intestinal microbiota, a total of 200, 1-d-old male Arbor Acres broiler chickens (46.53 ± 0.42 g) were selected for a 42-d experiment. Dietary treatments included a basal diet of corn-soybean meal supplemented with either 0 mg/kg (CON), 50 mg/kg aureomycin (ANT), 20 mg/kg rhLYZ (LOW), 60 mg/kg rhLYZ (MEDIUM), or 180 mg/kg rhLYZ (HIGH). Compared with CON, MEDIUM diet increased (P < 0.05) average daily gain (67.40 g) of broilers from day 22 to 42. In the early (1.29) and overall phases (1.69), MEDIUM led to a reduction (P < 0.05) in the feed conversion ratio of broiler chickens. Furthermore, in comparison to the CON and ANT, MEDIUM exhibited reduced (P < 0.05) levels of INF-γ and tumor necrosis factor-α in the serum. In the cecum, the abundance of Monoglobus and Family_XIII_AD3011_group was lower (P < 0.05) in the MEDIUM treatment compared to CON. Overall, supplementation of 60 mg/kg of rhLYZ improved growth performance, nutrient utilization efficiency, and serum immune function, while also influencing the composition of intestinal microbiota. This suggests lysozyme's potential to replace antibiotic additives in feed.