Enzyme-Assisted Valorisation of Ulva lactuca in Weaned Piglet Diets: GC-MS Insights into the Skeletal Muscle Metabolome

Marine macroalgae are promising feed resources, but their recalcitrant cell walls limit nutrient availability in monogastric animals. We evaluated the metabolome of the longissimus lumborum muscle in weaned piglets fed a control diet, a diet containing 7% Ulva lactuca (UL), or the UL diet supplemented with 0.01% recombinant ulvan lyase (ULU), using six animals per treatment. A GC-MS-based semi-targeted workflow quantified 70 metabolites. Principal component analysis showed extensive overlap among treatments, and partial least squares-discriminant analysis had limited predictive performance despite visual separation (R2 = 0.967; Q2 = 0.313). At an unadjusted pairwise level, 32 metabolites differed between control and UL, 25 between control and ULU, and 20 between ULU and UL. After false discovery rate correction of the overall treatment test, only glutamine and nonadecanoic acid remained significant. Glutamine abundance was lower in UL than in control and ULU, whereas nonadecanoic acid was higher in both seaweed-fed groups than in control. Overall, dietary U. lactuca, with or without ulvan lyase supplementation, preserved the global muscle metabolome. Given the relatively small sample size and the lack of functional confirmation, further studies are required to validate these observations.