Crude Glycerin Modulates the Proteomic Profile and Epithelial Adaptation of Ruminal Papillae in Lambs Fed High-Concentrate Diets

Crude glycerin (CG) is an energy-dense ingredient capable of partially or fully replacing corn in high-concentrate diets for ruminants. Its rapid ruminal absorption, favorable fermentative profile, and absence of lactic acid production may support safer adaptation to intensive feeding systems. The aim of this study was to evaluate the effects of replacing corn with CG (300 g/kg DM) on growth performance, feeding behavior, rumen morphometry, and proteomic responses of ruminal papillae in feedlot lambs. Sixty-five Santa Inês × Dorper lambs were assigned to either a control diet or a diet containing CG and were evaluated during pre-adaptation, adaptation, and finishing phases. Replacing corn with CG slightly reduced average daily gain (p = 0.02), without affecting final body weight, dry matter intake, or carcass yield (p > 0.05). Lambs fed CG exhibited lower subcutaneous fat thickness (p = 0.04) and reduced neutral detergent fiber intake during feeding behavior assessments (p < 0.05). Rumen papillae showed higher mitotic index and greater epithelial activity throughout the feedlot period, regardless of treatment. Proteomic analysis revealed upregulation of proteins involved in epithelial integrity (Claudin-1, Occludin) and mitochondrial energy metabolism (ATP synthase β, glycerol kinase) in CG-fed lambs, alongside downregulation of proteins related to oxidative stress and inflammation (HSP70, Annexin A1, SOD1, Peroxiredoxin-6). These findings demonstrate that CG promotes beneficial molecular adaptations in the ruminal epithelium without compromising carcass traits, supporting its use as a safe, functional, and sustainable alternative to corn in lamb finishing systems.