Effects of different dietary selenium sources on growth performance, antioxidant capacity, meat quality, and gut microbiota in growing-finishing pigs

Selenium (Se) is an essential trace element for humans and animals, and its biological functions and bioavailability are highly dependent on the forms of Se. However, direct comparisons of different Se sources under the same supplementation level in growing-finishing pigs remain limited. The purpose of this study was to compare the effects of sodium selenite (SeS), selenomethionine (SeM), and nano-Se (SeN) in growing-finishing pigs. Seventy-five Duroc × Large White × Landrace pigs (25.39 ± 0.41 kg weight, 70-d age) were randomly assigned to 3 treatments (5 pens/treatment, 5 pigs/pen) for 100 d and fed a basal diet supplemented with 0.35 mg/kg Se from SeS, SeM, or SeN. Growth performance and carcass traits did not differ among treatments ( P > 0.05). The SeN group increased serum total antioxidant capacity (T-AOC) compared to SeS and SeM, and increased T-AOC in liver and longissimus dorsi muscle (LDM) compared to SeM ( P < 0.05). The SeM group reduced malondialdehyde (MDA) compared to SeS ( P = 0.046), whereas the SeN group tended to increase LDM glutathione (GSH; P = 0.058) and decrease MDA ( P = 0.061). Kidney Se concentration was higher in SeM than SeN ( P = 0.036) and tended to exceed SeS ( P = 0.074). For meat quality, SeM and SeN lowered yellowness (b* 24 h ) compared to SeS, and SeN increased inosine monophosphate compared to the other sources ( P < 0.05). In LDM, the SeM group decreased muscle fiber diameter and increased fiber density compared to SeN, with higher MyHCI and lower MyHCIIx expression ( P < 0.05). The mRNA expression levels of FAS and PPARγ were upregulated by SeM and SeN compared to SeS ( P < 0.05). The SeN group also upregulated ACCα and tended to downregulate HSL ( P = 0.083). Cecal microbiota analysis showed higher Chao1 and Shannon indices in SeN than SeS groups ( P < 0.05), whereas β-diversity did not differ among treatments. Nevertheless, different Se sources impacted the compositional abundance of multiple microbial phylotypes. Spearman correlation analysis revealed significant associations between multiple taxa and meat quality traits, including a positive correlation between Christensenellaceae R-7_group and intramuscular fat content ( P = 0.043). Collectively, Se source had a limited impact on growth performance but exerted distinct effects on antioxidant capacity, kidney Se concentration, selected meat quality traits, muscle fiber characteristics, and microbial profiles in growing-finishing pigs.