Supplementation of L-Lactic Acid Regulates Antioxidant Capacity and Improved Intestinal Integrity and Microbial Diversity in Weaned Piglet

The effects of dietary L-lactic acid (L-lactic acid or LAC) supplementation in weaned piglets were investigated. 24 healthy weaned piglets (Duroc × Yorkshire × Landrace) (body weight = 8.76 ± 0.42 kg) were randomly assigned into 4 treatments with 6 replicate pens per treatment and 1 piglet per pen. The treatment consisted of basal diets serves as control and groups supplemented with 0.5% (LAC0.5%), 1% (LAC1%) or 2% of L-lactic acid (LAC2%), respectively. We examined the growth performance, oxidative status, immune, inflammatory biomarkers, lactate transporters associated genes and caecal microbial composition. The results showed that growth performance (final body weight, feed intake and feed conversion) was not affected by LAC supplementation. However, higher (P < 0.01) antioxidant capacity, immune and metabolic biomarkers were observed. Positive effects on increased of metabolic biomarkers including acetoacetate, β-hydroxybutyrate and lactate dehydrogenase (P < 0.001), pro-inflammatory cytokines (TNF-α, IL-8; P < 0.01) and anti-inflammatory IL-10 (P < 0.01) were found. In contrast, Immunoglobulins (IgA, IgG and IgM) decreased (P < 0.01) in response to LAC treatments. Expression of lactate transport genes (MCT1, MCT2 and MCT4) increased (P < 0.01) in colon but decreased in muscle. Microbial composition and richness were not affected but taxa such as Lactobacillus, Faecalibacterium and Christensenellaceae_R-7_group were enriched (FDR P < 0.05) in LAC05% and LAC1%. Adverse effects were observed on intestinal morphology such as progressive villous atrophy and crypt hyperplasia in LAC1% and LAC2% treatments but not in LAC0.5%. Overall, while growth performance was largely not affected, low level of LAC supplementation (0.5%) appeared to be safely used in weaning piglets while higher levels (1–2%) could negatively impact intestinal health and immune status of weaned piglets.