Differential effect of two dietary protein sources on time course response of muscle anabolic signaling pathways in normal and insulin dysregulated horses

Caroline M.M. Loos, Kyle R. McLeod, Eric S. Vanzant, Sophie A. Stratton, Adam D. Bohannan, Robert J. Coleman, David A. van Doorn, Kristine L. Urschel

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


The objective of the study was to characterize the temporal changes of phosphorylation patterns of mTOR signaling proteins in response to two dietary protein sources in insulin dysregulated (ID, n = 8) and non-ID (n = 8) horses. Horses were individually housed and fed timothy grass hay and 2 daily concentrate meals so that protein was the first limiting nutrient and the total diet provided 120% of daily DE requirements for maintenance. On sample days, horses randomly received 0.25 g CP/kg BW of a pelleted alfalfa (AP) or commercial protein supplement (PS). Blood samples were collected before and 30, 60, 90, 120, 150, 180, 210, 240, 300, 360, 420, and 480 min post feeding and analyzed for plasma glucose, insulin and amino acid (AA) concentrations. Gluteus Medius muscle samples were obtained before and 90, 180, and 300 min after feeding and analyzed for relative abundance of phosphorylated mTOR pathway components using western immunoblot analysis. There was no effect of protein source on postprandial glucose and insulin responses (P ≥ 0.14) but consumption of PS elicited a 2 times larger AUC for essential AA (EAA), greater peak concentrations of EAA and a shorter time to reach peak EAA concentrations compared to AP. Abundance of phosphorylated mTOR (P = 0.08) and rpS6 (P = 0.10) tended to be ~1.5-fold greater after consumption of PS at 90 min compared to AP. Dephosphorylation patterns differed between protein sources and was slower for AP compared to PS. ID horses had a 2 times greater (P = 0.009) AUC and 3 times higher postprandial peak concentrations (P < 0.0001) for insulin compared to non-ID horses after consumption of both treatment pellets, but EAA responses were similar between groups (P = 0.53). Insulin status did not affect rpS6 or mTOR phosphorylation after consumption of either protein source (P ≥ 0.35), but phosphorylated rpS6 abundance was twice as high in ID compared to non-ID horses (P = 0.007). These results suggest that the consumption of higher quality protein sources may result in greater postprandial activation of the mTOR pathway compared to equal amounts of a forage-based protein source. Moreover, ID does not impair postprandial activation of mTOR and rpS6 proteins in horses following a protein-rich meal.

Original languageEnglish
Article number896220
JournalFrontiers in Veterinary Science
StatePublished - Aug 1 2022

Bibliographical note

Funding Information:
This project was supported by Versele-Laga (Deinze, Belgium) and the National Institute of Food and Agriculture, U.S. Department of Agriculture Hatch Program under KY0070109. Mention of trade name, proprietary product, or specified equipment does not constitute a guarantee or warranty by the University of Kentucky and does not imply approval to the exclusion of other products that may be available.

Funding Information:
Researchers would like to thank Chad Tucker and the rest of the Department of Veterinary Science staff and all undergraduate volunteers for their support with animal care, sample collection and completion of this project.

Publisher Copyright:
Copyright © 2022 Loos, McLeod, Vanzant, Stratton, Bohannan, Coleman, van Doorn and Urschel.


  • horse
  • insulin dysregulation
  • mTOR
  • muscle
  • protein source

ASJC Scopus subject areas

  • Veterinary (all)


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