Published February, 2010

Lysine is one of the 20 amino acids essential to horses, but it often is the most deficient in their diets due to its inadequate levels in commonly-fed cereal grains. Amino acids are the building blocks of protein, which form muscle, enzymes, and hormones throughout the body. Horses can only use them if all essential amino acids are present at sufficient levels. If one amino acid, such as lysine, is deficient, the horse's body will use it up and convert the excess of the remaining amino acids into carbon dioxide, which is exhaled, and to urea, which is excreted in the urine.

Kristine Urschel, PhD, an assistant professor in animal and food Sciences for the University of Kentucky (UK) College of Agriculture, was awarded a $150,000 grant from the USDA's Agricultural and Food Research Initiative, and the National Institute of Food and Agriculture to study lysine requirements in horses.

"Receiving funds for research through USDA- AFRI is a great achievement for two reasons," said Nancy Cox, associate dean for research in UK's College of Agriculture, Kentucky Agricultural Experiment Station director and administrative leader for UK's Equine Initiative. "One, this program is so competitive that few researchers land funding on the first try. Also, it is much harder to secure funding for equine research, since more than 90% of USDA animal research is on food animals."

"Dr. Urschel is to be congratulated for this phenomenal success," Cox said.

Adequate levels of lysine are particularly critical for young horses, since they require more protein than adults to support their rapid growth rates. Although scientists have completed studies to determine what levels of lysine in a diet are adequate or inadequate for growth, Urschel said her study will be the first to assess exactly what amount is ideal.

"Hopefully, it will be a starting point for determining other amino acid requirements in the diet," Urschel said.

Urschel came to UK in August 2008 after completing her bachelor's and doctoral degrees at the University of Alberta, Canada, and completing post-doctoral research at Virginia Polytechnic Institute and State University (Virginia Tech). She began her equine research while at Virginia Tech, which led to an interest in this species' metabolism and nutrition.

Her study will also be the first of its kind to use the Indicator Amino Acid Oxidation (IAAO) technique for determining amino acid requirements in horses. Scientists use this technique to measure the amount of carbon dioxide produced by the breakdown of an alternate amino acid. Urschel will be able to determine the optimal amount of lysine when she detects the least amount of carbon dioxide released from overall amino acid breakdown. Urschel will feed study horses varying amounts of lysine and measure using IAAO until the optimum level of lysine is reached.

Urschel believes the various potential applications of the study made the research appealing to the USDA Animal Growth and Nutrient Utilization group's funding review committee.

"Some techniques such as IAAO haven't been used to measure lysine in horses, but the same techniques are cutting-edge in other species," Urschel said. "I think this particular funding group recognized that we don't know a lot about horses' amino acid and protein requirements, but it's important that we do.

"Although amino acid requirements can be met by simply feeding high levels of total protein, this is not a desirable approach," she said.

She added that feeding excess protein leads to inefficient digestion and excretion of nitrogen, which can negatively impact the environment.

Urschel said she hopes the results of the study will help people feed their horses, whether they are young and growing or adults, more efficiently to maximize growth and minimize nutrient waste.

Natalie Voss is a UK equine communications intern and undergraduate student in equine science.