Microvillus in LBW Meishan Piglets Preserved Microvillus Integrity Alongside Impaired Intestinal Barrier Function in Low-Birth-Weight Meishan Neonatal Piglets.

Despite lower birth weight, Meishan piglets exhibit a notably higher pre-weaning survival rate compared to Western commercial breeds. This study aimed to evaluate the effect of low birth weight (LBW) on intestinal barrier function in Meishan neonates. Six pairs of neonatal piglets (one normal birth weight, NBW: 0.85 ± 0.06 kg; one LBW: 0.65 ± 0.02 kg) from the same sow were euthanized at birth prior to suckling. Morphological parameters, goblet cell density, antioxidant enzyme activities, cytokine gene expression, and tight junction protein levels in the small intestine (SI) were assessed. Results showed that LBW piglets had a significantly higher SI length-to-body weight ratio (p < 0.05), along with reduced villus height, villus height-to-crypt depth ratio, and villus surface area in the jejunum and ileum (p < 0.01). Notably, microvillus structure remained intact despite the presence of mitochondrial swelling. LBW piglets also exhibited decreased goblet cell numbers, lower antioxidant capacity, dysregulated expression of cytokines (CD8, IFNγ, IL4, IL2), and reduced levels of mucin 2, ZO-1, and occludin (p < 0.05). In conclusion, although LBW Meishan piglets showed impairments in multiple aspects of intestinal barrier function, the structural integrity of the microvillus was preserved, which may contribute to their higher survival rate and represents a key adaptive advantage over commercial pig breeds.