Fresh research opens the door to potentially tailoring amino acid supplementation in horses to improve their general wellbeing and meet their demands in heavy training.
Researchers in Australia have used computer modelling to examine amino acid turnover in horses during training and racing.
They say their technique could be the basis for developing a novel supplementation strategy.
University of Newcastle researcher Hugh Dunstan and his colleagues pointed to the increased metabolic demands in horses to support the more intensive levels of exercise and recovery involved in heavy training for racing and competition.
“However, little is known at the metabolic level about amino acid turnover and the specific alterations of demand caused by high intensity exercise,” they said in the open-access journal, PLOS ONE.
During exercise, certain amino acids are required in greater quantities due to disproportionate losses through excretory systems and use in biosynthetic pathways.
The study team built a theoretical computer model in a bid to bring together the published rates of protein intake and used it to understand how some amino acids might be in higher demand than others.
It was set up to assess the final daily balances of amino acids for the horse in heavy training by assessing protein intake, utilisation and excretion rates from various studies.
To develop the model, they had to take urine samples from Standardbred horses before morning training to determine the proportions of amino acids excreted to accurately integrate amino acid turnover into their calculations.
The model indicated that, after evaluation of the daily amino acid turnover, glutamine/glutamic acid, serine and ornithine were in negative nitrogen balance, which identified these amino acids as critical limiting factors for anabolism.
Anabolism involves metabolic pathways that construct molecules from smaller units, together with the storage of energy.
Adjustment of the model to cater for high-intensity training indicated that extra demand was placed on eight amino acids, including glutamine/glutamic acid, valine, lysine, histidine and phenylalanine, which could become limiting if in short supply.
“The modelling results indicated that an amino acid supplement with the correct amino acids to match demand could theoretically be beneficial to a 500 kilogram horse in quantities of 20 to 80 grams a day,” they reported.
“These results open new avenues of research for specifically tailoring amino acid supplementation to meet demands for sports horses in heavy training and improving general well-being, especially in hotter climates.”
Discussing their findings, the study team noted that, in the racing industry, protein intake rates may actually reach levels up to 1500 grams per day for a horse — nearly double the recommendations contained in Nutrient Requirements of Horses, by the National Research Council of the National Academies.
On this basis, the model was run with the intake set at 3 grams per kilogram of bodyweight per day (1500 grams of protein a day for a 500kg horse) to determine the impact on the nitrogen balances of the amino acids. This left only ornithine (-3.4 grams) remaining in negative balance.
“This higher level of protein intake has indeed brought the horse into a positive balance for all the protein amino acids,” they said.
“However, the question is raised that, since most of the amino acids were in positive balance, perhaps this could be more effectively achieved by targeted amino acid supplementation with a lower feed intake closer to the recommended levels of 1.72g per kilogram of bodyweight per day.”
Targeted amino acid supplementation at quantities of 40-160mg per kilogram of bodyweight per day (20-80g/day for a 500kg horse) could have real benefits for maintaining a positive nitrogen balance and thus reduce demand on muscle turnover for supply, they said.
This represented just 2.3 to 9.3% of the total protein intake for the horse.
“Applied research with horses is now required to determine whether this supplementation approach can be effective in a range of breeds and competition formats.
“Future research should also focus on ascertaining specific amino acid requirements at various stages of training and competition to determine whether there would be long term benefits for horses such as better maintenance of muscle mass, optimising performance and reducing muscle damage.”
The full study team comprised Dunstan, Margaret Macdonald, Brittany Thorn and Timothy Roberts, all with the University of Newcastle; and David Wood, with Horsepower Pty Ltd.
Dunstan RH, Macdonald MM, Thorn B, Wood D, Roberts TK (2020) Modelling of amino acid turnover in the horse during training and racing: A basis for developing a novel supplementation strategy. PLoS ONE 15(1): e0226988. https://doi.org/10.1371/journal.pone.0226988