Age Rather Than Supplementation with Oat β-Glucan Influences Development of the Intestinal Microbiota and SCFA Concentrations in Suckling Piglets

**Background:** The weaning period is highly stressful for piglets, often leading to enteric infections and post-weaning diarrhoea. Dietary fibre, particularly oat β-glucan, is known to stimulate beneficial gut bacteria and SCFA production in adult pigs, but its effects during the suckling period are poorly understood. This study aimed to determine whether early β-glucan supplementation could promote earlier maturation of the gut microbiota and increase SCFA production in suckling piglets.

**Methods:** Fifty piglets from five litters were allocated within each litter to either a β-glucan (BG) group or a control (CON) group, balanced for sex and birth weight. The BG group received an oral supplement of oat β-glucan (40 mg/kg BW, SweOat bran BG28, 28% soluble β-glucan, molecular weight 2000 kDa) three times per week from day 7 until weaning at 35 days. The CON group received water by syringe. Rectal swabs for microbiota analysis were collected from 10 piglets per group at weeks 1, 2, 3, and 4. Jugular vein plasma was collected at weeks 1, 3, and 4. At weaning, one piglet per treatment per litter was euthanized for collection of portal vein and jugular vein plasma, colon digesta, and intestinal tissue (ileum and colon). Microbiota was analysed by 16S rRNA gene sequencing (V3-V4 region, Illumina MiSeq). SCFA and caproic acid were quantified by LC-MS. Histological measurements included villus height, crypt depth, mucosal thickness, and muscularis externa thickness. Statistical analyses used mixed models with treatment, sex, age, and interactions as fixed effects, and piglet ID nested within sow ID as random. Multivariate analysis used PCoA and ANOSIM.

**Key Results:** No differences in body weight gain were observed between BG and CON piglets. Microbiota diversity (Shannon and Chao-1 indices) increased significantly with age (p < 0.001) but did not differ between treatments. PCoA and ANOSIM confirmed that age (p = 0.0001, R = 0.24) and litter (p = 0.0001, R = 0.45) significantly influenced microbiota composition, while treatment had no effect (p = 0.32, R = 0.013). At phylum level, Firmicutes, Bacteroidetes, and Proteobacteria dominated. At genus level, Escherichia, Bacteroides, Prevotella, and Lactobacillus comprised >50% of relative abundance. A treatment × age interaction was found for Escherichia (p < 0.05), with higher relative abundance in BG at week 4 (p = 0.003), and for Bacteroides (p < 0.05), with higher abundance in BG at week 1 (p < 0.05) but higher in CON at week 2 (p < 0.05). Lactobacillus decreased with age from ~9% to ~2% (p < 0.001), while Prevotella increased (p < 0.001). Plasma SCFA concentrations were mainly affected by age. Acetic acid was lower in BG than CON (p < 0.05), but this likely reflected baseline differences. Acetic, propionic, butyric, iso-butyric, and valeric acid increased with age (p < 0.05 to p < 0.001), while formic and succinic acid decreased (p < 0.001 and p < 0.05, respectively). No significant treatment effects were found for SCFA in colon digesta or portal/jugular vein plasma from euthanized piglets. Histological parameters (villus height, crypt depth, mucosal thickness) did not differ between groups. Several correlations were identified: Prevotella was positively correlated with acetic acid (r = 0.42, p = 0.0008), S24_7:g was positively correlated with acetic (r = 0.55, p = 0.000005), propionic (r = 0.34, p = 0.007), and butyric acid (r = 0.49, p = 0.00005). Lactobacillus was negatively correlated with acetic acid (r = −0.46, p = 0.0002) and positively with succinic acid (r = 0.36, p = 0.005).

**Clinical Implications:** This study demonstrates that oat β-glucan supplementation at 40 mg/kg BW three times per week during the suckling period does not significantly alter gut microbiota development, SCFA production, or intestinal morphology in piglets. The dominant influence of age and litter effects suggests that early-life microbial colonisation is primarily driven by host development and environmental factors rather than by cereal β-glucan intervention. The lack of effect may relate to the immature gut microbiota's limited capacity to ferment β-glucan, the dosing regimen, or cross-contamination within litters. Higher doses or more frequent administration, or the use of β-glucans from microbial sources with higher bioactivity, might yield different results. The study underscores the importance of the suckling period as a critical window for microbiota establishment and highlights that interventions aimed at modulating gut health may need to target the post-weaning period or use alternative prebiotic strategies.