Dietary stevioside supplementation improves antioxidant status, carcass traits, and meat quality in growing-finishing pigs

Steviol glycosides (stevioside, STE) are natural, non-caloric sweeteners derived from Stevia rebaudiana that possess antioxidant, anti-inflammatory, and metabolic-regulatory properties potentially beneficial for livestock production, but their effects in growing–finishing pigs remain largely unexplored. We hypothesised that dietary STE supplementation would improve antioxidant status and thereby enhance carcass traits and pork quality in growing–finishing pigs. A total of 36 pigs (initial body weight 28.00 ± 0.41 kg) were randomly allotted to two dietary treatments (six replicate pens per treatment, three pigs per pen) and fed a basal diet with or without 200 mg/kg STE for 90 days. Dietary STE improved average daily gain (ADG) and the feed-to-gain ratio (F/G) during the early growing phase (25–50 kg; p < 0.05) and tended to increase final body weight over the entire trial. STE supplementation reduced serum urea and malondialdehyde (MDA) concentrations and increased serum immunoglobulin G (IgG), glutathione peroxidase (GSH-Px) activity, and total antioxidant capacity (T-AOC) (p < 0.05); in muscle, GSH-Px and total superoxide dismutase (T-SOD) activities increased and MDA concentration decreased (p ≤ 0.05), with no effect on T-AOC or catalase (CAT) activity. STE also increased carcass weight, carcass length, loin eye area, 24-h meat redness (a * 24 h), and intramuscular fat content (p < 0.05), but did not affect muscle protein content (p = 0.970). At the transcriptional level, STE downregulated myosin heavy chain (MyHC) IIb and upregulated MyHC IIa expression in the longissimus dorsi, and increased fatty acid synthase (FASN) mRNA expression in muscle while decreasing FASN, insulin-like growth factor 1 (IGF-1), and hormone-sensitive lipase (HSL) mRNA expression in liver. These gene expression changes are consistent with, but do not directly demonstrate, a shift towards a more oxidative muscle fibre profile and tissue-specific regulation of lipid metabolism; histological or protein-level confirmation is warranted. Overall, dietary supplementation with 200 mg/kg STE improved early-phase growth performance, antioxidant status, and several carcass and meat quality traits in growing–finishing pigs, supporting its potential as a functional feed additive; further dose–response studies are needed to identify the optimal inclusion level.