Plasma Amino Acid Concentrations of Horses Grazing Alfalfa, Cool-Season Perennial Grasses, and Teff.
Authors: DeBoer Michelle L, Martinson Krishona L, Kuhle Kerry J, Sheaffer Craig C, Hathaway Marcia R
Journal: Journal of equine veterinary science
Summary
# Editorial Summary Different forage species deliver markedly different amino acid profiles to grazing horses, yet this variation has limited impact on systemic protein synthesis—a finding with important implications for nutritional management. DeBoer and colleagues conducted a controlled grazing trial in which six horses rotated through alfalfa, cool-season grass mixtures, and teff pastures, with blood sampling at turnout and at 2 and 4 hours post-grazing, whilst corresponding forage samples were analysed for amino acid content and cultured equine muscle cells were exposed to harvested plasma. Cool-season grasses delivered the highest amino acid concentrations overall, whilst teff consistently provided the lowest, yet only plasma threonine differed significantly between treatments at the 4-hour mark—and this difference failed to translate into measurable changes in de novo protein synthesis in the muscle cell cultures. For practitioners, this suggests that whilst forage choice clearly influences what amino acids horses consume, the body's compensatory mechanisms appear robust enough that single-forage grazing decisions need not be driven primarily by amino acid composition concerns; however, the specific reduction in circulating threonine with teff grazing warrants further investigation in horses with heightened protein demands, such as growing youngstock or hard-working competition animals.
Read the full abstract on PubMed
Practical Takeaways
- •While forage type affects amino acid composition, this does not translate to meaningful differences in muscle protein synthesis, suggesting forage choice may not need to be optimized solely for amino acid profile in grazing horses
- •Cool-season grasses provided higher amino acid content than teff or alfalfa in this study, though practical significance for performance remains unclear given lack of protein synthesis response
- •Plasma threonine levels vary with forage type, but monitoring this single amino acid is unlikely to be clinically useful for assessing nutritional adequacy of grazing horses
Key Findings
- •Amino acid concentrations were generally lowest in teff forage and highest in cool-season grass forage (P ≤ 0.05)
- •Plasma threonine concentration was the only amino acid showing significant differences at 4 hours post-turnout among forage types
- •Despite significant differences in forage amino acid content, there was no effect on de novo protein synthesis in cultured equine myotubes treated with sera from grazing horses (P ≥ 0.20)