Impact of initial postweaning feed intake on weanling piglet metabolism, gut health, and immunity.

Low feed intake (FI) in weanling pigs can be hypothesized as both a cause and consequence of intestinal disturbances and metabolic stress. We explored the associations between individual daily FI patterns, metabolic status, and intestinal physiology. Female pigs (n = 24) were selected based on high or low cumulative FI between d1 and d3 relative to weaning (d0) from 12 pens equipped with electronic feeding stations at 1-wk after weaning for dissection and sampling. Four classes of pigs were created with pigs that started with a high or low FI (d1 to d3) and continued with a high or low FI (d4 to d6) (HH, HL, LH, and LL, respectively; n = 6) for data analysis. In plasma, HL pigs showed higher plasma glutamate dehydrogenase than LL pigs (P < 0.05). A low FI d1 to d3 increased plasma creatinine and lactate dehydrogenase, and reduced insulin-like growth factor (IGF-I), gastrointestinal organ weights, and jejunal villus surface area at 1 wk after weaning (P < 0.05). However, low FI d4 to d6 increased plasma haptoglobin, PigMAP, bile acids, and bilirubin levels and reduced jejunal villus length (P < 0.05). In jejunum tissue, HH pigs had the highest jejunal upregulated IGF-I receptor and a reduced local inflammatory gene expression when compared to HL pigs (MyD88), and similarly, when compared to all classes (FAXDC2). For the main effects, pigs classified as high FI d1 to d3 had upregulated immune systems including IL-6, TGFB1, TLR2, and TLR4 genes compared to low FI d1 to d3 pigs (P < 0.05). In a multivariate model, variance in average daily gain (R2 = 0.82) was mostly explained by positive correlations with FI d1 to d3, jejunal morphometrics, and plasma IGF-I, while negatively explained by histamine in digesta, and creatinine, PigMAP, triglycerides, and haptoglobin in plasma. In conclusion, pigs transitioning from high to a low FI showed distinct metabolic alterations and a subtle local inflammation masked by the vigorous local immune response in pigs with initial (d1 to d3) high FI. Pigs with an initial low FI had a fasting-like metabolic state, indicated by hepatic alterations pointing at shifting protein metabolism into energy production. Altogether, FI during the initial days postweaning significantly impacts pig growth, immunity, and metabolism, with a sustained low intake (i.e., up to 6 d) triggering a systemic inflammatory response.