Assessment of Components Associated with Average Daily Gain of Finishing Lambs Fed with Two Roughage Sources Using Integrative Metabolomics

Rapeseed straw and peanut vine are abundant agricultural by-products in China, but their low digestibility has largely restricted their application in ruminant production. Extrusion processing has been shown to improve the fiber structure and nutrient availability of roughages, yet the underlying metabolic mechanisms by which extruded rapeseed straw (ERS) influences growth performance remain insufficiently elucidated. This study aimed to explore the metabolic mechanisms of average daily gain (ADG) affected by rapeseed straw feeding through studying metabolites from four biological matrices (rumen fluid, serum, liver and muscle) collected from 24 Hu lambs fed extruded rapeseed straw (ERS, n = 12) and peanut vine hay (PVH, n = 12). The Hu lambs fed ERS exhibited greater ADG during the late finishing stage (60–90 d) than those fed PVH (p = 0.03). A total of 666, 274, 147, and 96 metabolites were identified in the rumen fluid, liver, serum and muscle, respectively. In addition, nine, 12, seven, and three significantly different metabolites (VIP > 1 and p < 0.05) related to eight significant pathways (starch and sucrose metabolism, galactose metabolism, glyoxylate and dicarboxylate metabolism, glycerophospholipid metabolism, phenylalanine, tyrosine and tryptophan biosynthesis, phenylalanine metabolism, Gly, Ser, and Thr metabolism, arginine biosynthesis, and purine metabolism) were identified in the four biological matrices between the ERS- and PVH-fed Hu lambs. Further integrated key metabolic pathway analysis showed that the ERS-fed Hu lambs may have more comprehensive amino acid and energy metabolisms with relatively fewer carbohydrate metabolisms, suggesting enhancing protein deposition and energy utilization efficiency with associated metabolites and pathways serve as key biomarkers for a higher ADG of Hu lambs when fed ERS.