Differential effect of two dietary protein sources on time course response of muscle anabolic signaling pathways in normal and insulin dysregulated horses.
Authors: Loos Caroline M M, McLeod Kyle R, Vanzant Eric S, Stratton Sophie A, Bohannan Adam D, Coleman Robert J, van Doorn David A, Urschel Kristine L
Journal: Frontiers in veterinary science
Summary
# Editorial Summary This 2022 investigation examined how two protein sources—alfalfa pellets versus a commercial protein supplement—influence muscle protein synthesis signalling in both metabolically normal and insulin dysregulated horses, recognising that protein quality and amino acid availability are key drivers of anabolic response. Using western blotting to measure phosphorylation of mTOR pathway proteins (the primary mechanism triggering muscle protein synthesis) at multiple timepoints after feeding, researchers compared eight insulin dysregulated and eight non-dysregulated horses that each received 0.25 g crude protein per kilogram bodyweight from either source. The commercial supplement produced a substantially greater amino acid availability profile—approximately double the area under the curve for essential amino acids, with peak concentrations reached more rapidly—and correspondingly showed 1.5-fold greater activation of the mTOR and rpS6 phosphorylation cascade at 90 minutes post-feeding, though this effect was slower to resolve with the alfalfa source. Critically, insulin dysregulation did not impair the muscle's capacity to activate these anabolic signalling proteins despite the marked hyperinsulinaemic response in affected horses, suggesting that protein-driven muscle synthesis remains available as a therapeutic target regardless of metabolic status. For practitioners managing horses with equine metabolic syndrome or insulin dysregulation, these findings support prioritising higher-quality, rapidly-available protein sources to maximise muscle protein synthesis responses, whilst reassuring that muscle anabolism itself remains intact in dysregulated animals.
Read the full abstract on PubMed
Practical Takeaways
- •Commercial protein supplements may stimulate muscle protein synthesis more effectively than forage-based proteins of equal amount, potentially supporting muscle development and recovery
- •Insulin-dysregulated horses can still activate muscle-building signaling pathways normally after protein feeding, suggesting protein quality rather than metabolic dysfunction limits their response
- •Consider higher-quality protein sources for ID horses requiring muscle support, as their amino acid and anabolic signaling responses remain intact despite insulin dysregulation
Key Findings
- •Commercial protein supplement elicited 2-fold greater essential amino acid area-under-curve and faster peak amino acid concentrations compared to alfalfa pellets
- •Phosphorylated mTOR and rpS6 tended to be 1.5-fold greater 90 minutes after commercial protein supplement consumption versus alfalfa
- •Insulin-dysregulated horses showed 2-fold greater insulin AUC and 3-fold higher peak insulin but similar essential amino acid responses to non-dysregulated horses
- •Insulin dysregulation did not impair mTOR or rpS6 phosphorylation responses to protein-rich meals, though basal rpS6 phosphorylation was twice as high in dysregulated horses