Early Weaning Impairs the Growth Performance of Hu Lambs Through Damaging Intestinal Morphology and Disrupting Serum Metabolite Homeostasis.

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This study aimed to evaluate the effect of early weaning (EW) on the growth performance, gastrointestinal development, serum parameters, and metabolomics of Hu sheep lambs. Twenty-four male Hu lambs were initially ewe-reared. A total of 12 lambs were weaned at 30 d of age (D30) as the EW group, and the remaining 12 lambs were weaned at 45 d of age (D45) as the control (CON) group. Serum samples were collected from six lambs per treatment on D30, D33, D36, and D45, and the lambs were slaughtered on D45 to collect the rumen and small intestine. The results showed that, compared with the CON group, the average daily gain (ADG), final body weight (p < 0.001), as well as average daily feed intake (ADFI) of lambs in the EW group significantly decreased in the first (p = 0.004) and second (p = 0.013) 5 days of treatment. Additionally, EW increased the ruminal weight and papillae length but reduced the duodenal villus height on D45 (p < 0.05). As for the serum parameters, the concentrations of glucose on D33, D36, and D45 (p < 0.001), and the IL-6 content on D45 (p = 0.018) were observed to be lower, while the levels of immunoglobulin A (IgA) (p = 0.027), IgG (p = 0.035), and IgM (p = 0.002) on the four ages were all higher in the EW group than those in CON group. Additionally, both treatment and age interactively affected the levels of GLU (p = 0.001), TP (p = 0.041), and IL-6 (p = 0.016). Additionally, the serum metabolomics analysis on D45 showed that the contents of 5-HT and arachidonic acid were increased, while L-phenylalanine, L-tyrosine, and L-glutamic acid were reduced in the EW group (p < 0.05). These differential metabolites were enriched in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, including inflammatory mediator regulation, protein digestion and absorption, and phenylalanine and tyrosine biosynthesis. The current results identify that EW at D30 decreased the growth performance (ADG and ADFI) of Hu lambs within two weeks post-weaning, which might be associated with impaired duodenal morphology and glucose metabolism. The serum metabolomics analysis revealed that EW altered the concentrations of 5-HT, phenylalanine, tyrosine, and arachidonic acid, which could serve as potential regulatory targets for modulating the health of EW Hu lambs.