Do dietary energy sources impact melatonin circadian patterns in the horse?

Open Access
Mcgowan, Lynn Silverman
Area of Honors:
Interdisciplinary in Animal Science and Immunology and Infectious Disease
Bachelor of Science
Document Type:
  • horse
  • circadian rhythm
  • melatonin
  • hydroxyproline
  • diet
  • bone development
Horses play a critical role in Pennsylvania’s agricultural industry, particularly through the food that they eat. In horses, high glycemic responses associated with high starch diets are connected with a number of health issues such as metabolic syndrome, insulin resistance, and laminitis. My research aimed to develop a more precise understanding of the links between different dietary energy sources and the metabolic and performance responses by horses. This study focused on melatonin, a metabolite shown to play key roles in digestive physiology and skeletal system health. Melatonin is secreted by the pineal gland in response to light and is controlled by a biological clock. I examined melatonin secretory patterns over a twenty-four hour period to see if they are influenced by diets that differ in their glycemic content. A crossover study design utilizing a total of twelve, six-month-old quarter horses fed either a high or low glycemic diet was applied over a six-week period. The concentration of melatonin in the blood at each two-hour interval was quantified over the full twenty-four hour period. Further, the levels of hydroxyproline in plasma across the day were quantified as a measure of bone turnover. By increasing our scientific knowledge of nutrient sensing systems, we will gain a better understanding of how the management of animals can be modified to improve growth and development of the horse.