Effects of dietary Hermetia illucens oil on rumen and serum metabolome profiles in lactating dairy cows

The dairy industry could make use of sustainable alternatives to conventional palm fat in ruminant nutrition. Insect-derived lipids, particularly the oil extracted from Hermetia illucens larvae ( H. illucens oil, HIO), show promise as an environmentally sustainable substitute. However, its effects on metabolic pathways and potential to replace fractionated palm oil (FPO) in lactating dairy cow diets remain insufficiently characterized. This study investigated the effects of HIO on the rumen and serum metabolome of lactating dairy cows. Twenty-six Valdostana Red Pied cows (parity = 3 ± 1.9; days in milk = 68 ± 27.5 d; BW = 556 ± 49.5 kg) were randomly assigned to receive either HIO or FPO (3% of the concentrate on as fed basis) for 50 days. Rumen fluid and serum samples were collected at the beginning (d 0, the day before starting the experimental diets administration) and end of the trial (d 50) for subsequent metabolomic analysis using liquid chromatography-mass spectrometry. A total of 7,590 rumen fluid and 8,061 serum features were detected, with 687 and 689 metabolites annotated, respectively. Principal component analysis (PCA) revealed stronger temporal than treatment effects. Serum metabolome showed slightly more pronounced responses to dietary HIO inclusion than rumen fluid, with 61 and 64 differential metabolites identified between HIO and FPO groups in rumen and serum, respectively. The pathway enrichment analysis based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) database revealed that HIO inclusion modulated metabolic pathways mainly related to amino acid and lipid metabolism. Specifically, metabolites such as N-acetyl-L-glutamate, imidazolepropionic acid, sulfate, and polyunsaturated fatty acids (e.g., stearidonic acid and dihomo-γ-linolenic acid) were significantly altered following HIO inclusion. In contrast, pathways related to glycolysis and starch metabolism remained largely unaffected. No adverse metabolic effects associated with the tested HIO inclusion level were detected. HIO may be a metabolically safe and more sustainable alternative to FPO in dairy cow diets at the given inclusion rate, without evidence of disrupting metabolic homeostasis.