Effects of lipoic acid on muscle quality in finishing pigs under diquat-induced oxidative stress challenge

The aim of this experiment was to investigate the effects of dietary lipoic acid (LA) supplementation on meat quality and antioxidant regulation mechanisms in finishing pigs subjected to oxidative stress challenge induced by diquat (DQ). A 2 × 2 factorial design was applied using 24 Large White barrows (70.64 ± 3.61 kg; n = 6 per group) assigned to Control, LA (800 mg/kg LA), DQ (8 mg/kg BW) and DQ + LA treatments. DQ was administered intraperitoneally on day 15, and pigs were slaughtered on day 29 for collection of Longissimus dorsi samples. Carcass traits, meat quality traits (pH, colour, drip loss and shear force), Nrf2/Keap1 protein levels, myofiber-related genes expression (MyHC isoforms), and SOD activity and expression were analysed. We found that LA and DQ showed limited effects on carcass traits, except for a significant DQ × LA interaction on backfat thickness. DQ reduced pH24 h and increased L24 h, indicating accelerated post-mortem acidification and altered meat colour. LA increased a45 min and significantly affected shear force, with a pronounced interaction under oxidative stress. DQ markedly upregulated Nrf2 protein expression, while LA partially attenuated this increase without affecting Keap1. DQ and LA significantly modulated myofiber type-related genes, with stress-dependent interactions observed for MyHC I and MyHC IIb. Moreover, DQ enhanced SOD mRNA, protein expression and enzyme activity, whereas LA increased SOD mRNA expression independently of oxidative stress, with no significant interaction effects. In conclusion, dietary LA modulated antioxidant capacity and muscle fibre gene expression in finishing pigs challenged with DQ; However, its effects on meat quality were stress-dependent rather than uniformly beneficial, indicating that further studies are needed to clarify its role in maintaining overall pork quality under diquat-induced oxidative stress challenge.