Dietary crude protein intake influences rates of whole-body protein synthesis in weanling horses.
Authors: Tanner S L, Wagner A L, Digianantonio R N, Harris P A, Sylvester J T, Urschel K L
Journal: Veterinary journal (London, England : 1997)
Summary
# Dietary Crude Protein Intake and Protein Synthesis in Weanling Horses Optimal amino acid balance during weaning is critical for supporting growth, yet little is known about how different protein intakes affect whole-body protein metabolism in young horses. Researchers used stable isotope tracer methodology—infusing labelled phenylalanine and bicarbonate whilst monitoring plasma enrichment—to measure protein kinetics in weanling horses fed either a commercial-level concentrate (4.1 g crude protein/kg bodyweight daily) or a recommended-level concentrate (3.1 g crude protein/kg bodyweight daily), with both groups consuming identical forage. The higher-protein diet elicited greater postprandial plasma amino acid responses across multiple essential and non-essential amino acids; however, the recommendation-level diet paradoxically showed increased phenylalanine oxidation and reduced non-oxidative phenylalanine disposal, indicating lower whole-body protein synthesis rates despite similar phenylalanine intake between groups. This suggests that feeding to *minimum* recommended crude protein levels may create an amino acid imbalance that limits protein deposition in growing horses. For practitioners involved in weanling nutrition, these findings underscore the risk of underfeeding protein and the importance of considering amino acid balance—not merely total crude protein quantity—when formulating concentrate rations for young stock.
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Practical Takeaways
- •Current recommended crude protein levels for weanling horses may not support optimal protein synthesis rates; commercial concentrate formulations providing higher crude protein demonstrate more favorable amino acid kinetics
- •Amino acid balance appears more important than absolute lysine content alone—the recommended diet had adequate lysine but suboptimal other amino acids, limiting overall protein utilization
- •Weanling horses fed minimum recommended crude protein levels may benefit from concentrate formulations closer to commercial standards to maximize growth and development
Key Findings
- •Horses receiving commercial crude protein diet (4.1 g CP/kg BW/day) showed greater baseline plasma amino acid concentrations for 8 amino acids compared to recommended crude protein diet (3.1 g CP/kg BW/day)
- •Horses on recommended crude protein diet had significantly greater phenylalanine oxidation rates (P=0.02) and lower non-oxidative phenylalanine disposal rates (P=0.04)
- •Lower whole-body protein synthesis on the recommended crude protein diet indicates presence of limiting amino acid(s) despite adequate lysine provision