Dose-dependent effects of hydrolysed yeast on gut microbial diversity, growth performance, antioxidant activity, and meat quality in densely stocked broilers

Abstract

The search for effective alternatives to antibiotic growth promoters (AGP) has intensified due to increasing concerns regarding antimicrobial resistance and antibiotic residues in poultry products. Hydrolysed yeast (HY) has emerged as a promising functional feed additive with potential benefits for growth performance, immune function, and product quality in broilers. This study evaluated the effects of graded dietary HY supplementation on growth performance, carcass characteristics, meat quality, oxidative stability, and gut microbial diversity in broilers reared under high stocking density. A total of 900, one-week-old male Ross 308 broilers were randomly allocated to 36 pens (25 birds/1.2 m²) and assigned to six dietary treatments with six replicates each, in a completely randomised design. The treatments were a standard diet with 0.05% AGP (PCON), diet without an AGP (NCON), or the NCON diet supplemented with 0.025 (HY25), 0.05 (HY50), 0.075 (HY75), or 0.10% HY (HY100). Dietary HY supplementation influenced growth performance primarily during the starter and grower phases. Feed intake, body weight gain, and feed conversion ratio were affected ( P < 0.05), with birds receiving the HY75 diet exhibiting lower body weight gain and poorer feed efficiency than the other treatments, whereas overall growth performance was not affected ( P > 0.05). Hydrolysed yeast supplementation increased haematocrit ( P = 0.048) and reduced plasma malondialdehyde concentrations ( P < 0.001), while serum phosphorus concentration was lower in HY-supplemented birds than in the negative control ( P = 0.046). Relative breast yield was reduced only in birds fed the HY75 diet ( P < 0.001), whereas carcass weight, visceral morphometry, and meat quality traits were largely unaffected ( P > 0.05). Meat pH and colour exhibited significant quadratic responses to increasing dietary hydrolysed yeast inclusion ( P < 0.05), although treatment effects were limited. Alpha (α) diversity indices did not differ significantly ( P > 0.05) among dietary treatments. Hydrolysed yeast supplementation had inclusion-dependent effects in densely stocked Ross 308 broilers. The HY75 diet reduced early growth performance and breast yield, while overall performance and most carcass, visceral, and meat quality traits were unaffected. Hydrolysed yeast reduced plasma malondialdehyde concentrations, suggesting improved oxidative status under high stocking density conditions. Not applicable.