PROTEIN QUALITY
NOT QUANTITY FOR GROWING HORSES
JUNE 2020
Written by Performance Horse Nutrition
It is not enough that a horse’s diet contains an adequate amount of protein, but the quality of protein also becomes very important especially in young, growing horses and broodmares. Protein quality refers to the amount and ratios of essential amino acids. Protein quality and amino acid profile can alter how much protein the horse actually requires. While we often just discuss protein requirements generically as a percentage, the question still remains – can a lower total amount of protein be fed if it is of higher quality?
Researchers at Virginia Tech examined the effect of dietary protein quality on growth of Thoroughbred foals and yearlings. The authors proposed that the quantity of protein may be decreased by an improvement in protein quality, such as digestibility and amino acid profile. Protein quality may be improved by supplementation with amino acids that are limiting to protein synthesis. Lysine was identified as the first-limiting amino acid and Threonine was found to be the second-limiting amino acid. Protein status and growth were studied in 22 Thoroughbred foals from birth to 14 mo of age. The control supplement contained 14% CP. The experimental supplement was similar in ingredient composition except that it contained 9% CP plus 0.6% L-lysine and 0.4% L-threonine.
This study found that an improvement in the quality of protein fed to growing horses would enhance growth rates. The authors reported 1) no difference between treatment groups over the observational period for any of the indicators of protein status and 2) periods of nutritional stress marked by greater weight gain in the group fed the amino acid-fortified feed. This evidence substantiates the role of protein quality in maintaining growth and suggests that fortification with lysine and threonine will permit a decrease in quantity of protein fed while promoting optimum growth in Thoroughbred foals.
Staniar, W.B., D. S. Kronfeld, J. A. Wilson, L. A. Lawrence, W. L. Cooper and P. A. Harris. 2001. Growth of thoroughbreds fed a low-protein supplement fortified with lysine and threonine. J ANIM SCI, 79:2143-2151.