Theses and Dissertations

ORCID

https://orcid.org/0000-0002-0645-0606

Advisor

Cavinder, Clay

Committee Member

Lemley, Caleb

Committee Member

Smith, JohnEric

Committee Member

Dihn, Thu

Date of Degree

5-15-2026

Original embargo terms

Immediate Worldwide Access

Document Type

Dissertation - Open Access

Major

Agricultural Science (Animal and Dairy Science)

Degree Name

Doctor of Philosophy (Ph.D.)

College

College of Agriculture and Life Sciences

Department

Department of Animal and Dairy Sciences

Abstract

Exercise is a necessary component of athletic conditioning but imposes substantial physiological stress on horses, resulting in oxidative stress, inflammation, muscle damage, and thermal strain that can impair performance and recovery. Melatonin, a neurohormone with potent antioxidant and thermoregulatory properties, has been proposed as a novel nutritional strategy to mitigate these effects. This dissertation aimed to (1) characterize serum melatonin concentrations following oral supplementation, (2) evaluate the effects of melatonin on oxidative stress, inflammation, and muscle damage biomarkers after exercise, and (3) examine its influence on physiological parameters during exercise under warm weather conditions. Across a series of controlled experiments using mature stock-type mares, horses received either 0, 20, or 50 mg of oral melatonin prior to standardized submaximal exercise bouts. Blood samples were analyzed for melatonin, thiobarbituric acid reactive substances (TBARS), superoxide dismutase (SOD), glutathione peroxidase (GPx), total antioxidant capacity (TAC), serum amyloid A (SAA), creatine kinase (CK), and lactate dehydrogenase (LDH). Physiological responses including heart rate, respiratory rate, internal temperature, and surface body temperature were also recorded. Melatonin supplementation produced a dose-dependent increase in circulating concentrations, with the 50 mg dose exceeding natural nocturnal peaks and maintaining elevated levels for up to eight hours post-administration. Horses supplemented with melatonin demonstrated reduced TBARS concentrations and enhanced SOD and GPx activity, suggesting improved redox balance. Serum amyloid A, CK, and LDH responses were attenuated in supplemented groups, indicating diminished inflammatory and muscle-damage responses. Under summer conditions, melatonin-treated horses exhibited lower heart rate, respiratory rate, and body temperature during recovery, consistent with enhanced thermoregulatory efficiency. Collectively, these findings demonstrate that oral melatonin supplementation effectively elevates circulating hormone levels and confers measurable physiological benefits by reducing oxidative, inflammatory, and thermal strain associated with exercise. Melatonin represents a promising adjunct for supporting recovery, performance, and welfare in equine athletes; however, further research is warranted to refine dosing strategies, evaluate long-term safety, and determine its impact on competitive performance outcomes.

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