Dairy polar lipids have demonstrated anti-inflammatory properties and protective effects on intestinal integrity, potentially mitigating the adverse impacts of weaning in piglets by modulating microbiota composition and intermediary metabolism. This study evaluated a dairy by-product rich in polar lipids on the microbiome and plasma lipid mediators of weaned piglets. A total of 240 male piglets (21 days old; 6.3 ± 0.5 kg) received either a soybean lipid-based diet (SD) or a polar lipid-based diet (PD) from weaning to day 21, followed by a common diet until day 42. Within each diet, animals were provided with one of the three milk replacers (MRs) for the first 7 days: (1) Commercial MR (CO); (2) Polar lipid-based MR (PO); and (3) Soybean lipid-based MR (SO). Fecal and plasma samples were analyzed to assess microbial composition and lipid mediator profiles. Taxonomical distance between diets increased over time, whereas MR type had no effect. The PD diet significantly altered microbiota composition, increasing, for instance, the relative abundance of Firmicutes-belonging genera of the Lachnospiraceae family (Coprococcus, Roseburia), and increasing levels of ethanolamides (e.g., AEA, PEA, SEA, and DPEA). In contrast, the SD diet increased pro-inflammatory lipid mediators (e.g., 13-HODE, 13-KODE) derived from linoleic acid. Polar lipid supplementation in diet, but not in MRs, influenced microbiota diversity and lipid mediator profiles, suggesting a potential long-term impact on immune regulation and metabolism, highlighting their potential to enhance resilience during early-life stress. Future studies should explore these effects under traditional weaning conditions or other stress models.

Subacute ruminal acidosis (SARA) is a common metabolic disorder in ruminants fed high-concentrate diets. This study hypothesized that the abundance of lactate dehydrogenase gene (ldh) in the rumen could predict the individual animal’s susceptibility to SARA. A total of 121 Hu lambs were used in the study, and ldh gene abundance was inferred by PICRUST based on 16S rRNA gene sequencing. From this population, two extreme cohorts were screened, including six lambs with the highest ldh gene abundance (HLDH group) and six lambs with the lowest ldh gene abundance (LLDH group). Subsequently, the selected lambs were challenged with a SARA-risk diet, and metagenomic sequencing technology was conducted for comparative analysis of microbial functions between the two groups. Key findings revealed that HLDH lambs exhibited the following characteristics: (1) significantly higher ldh abundance as verified by metagenomic method (P < 0.001); (2) lower rumen pH with significantly prolonged duration below the 5.8 threshold (P < 0.001); (3) a tendency to reduced total bacterial abundance (P = 0.055); (4) significantly increased molar proportion of acetate (P = 0.02); and (5) suppressed carbohydrate metabolic pathways, with tendency of decreased abundance of glycoside hydrolase family (P ≤ 0.07). Notably, the rumen microbiome of the HLDH group showed significantly higher abundance of genes encoding pyruvate ferredoxin oxidoreductase (porA-D) (P < 0.001). In conclusion, the relative abundance of the ldh gene in the rumen can serve as a biomarker for predicting the susceptibility of lambs to SARA when fed highly fermentable diets, providing theoretical basis and technical support for the early warning and precise prevention of SARA.