Date of Graduation


Document Type


Degree Name

Doctor of Philosophy in Animal Science (PhD)

Degree Level



Animal Science


Charles Rosenkrans

Committee Member

Rick Rorie

Second Committee Member

Yvonne V. Thaxton

Third Committee Member

Mike Looper

Fourth Committee Member

Mark Russell


Biological sciences, Equine biomarkers, Miniature horses, Quarter horses, Throughbred horses


The objective of this study was to evaluate relationships among genetic and physiological biomarkers and phenotypic characteristics in horses. Three breeds (Quarter Horse, Thoroughbreds, Miniatures), and five genes of interest (leptin, ghrelin, cytochrome P450, glucocorticoid receptor, and lactate dehydrogenase) were the basis of the investigation. Genomic DNA was extracted from buffy coat samples of Quarter Horses (n = 21), Thoroughbreds (n = 26), and Miniatures (n = 34). Data were analyzed using MIXED MODEL procedures of SAS, with the main effects of breed and SNP genotype. Horse was the experimental unit, and dependent variables were classified as physical, cell differentials, and blood components. When the main effect F-test was significant (P < 0.05), means were separated using multiple T-tests. We identified three single nucleotide polymorphism (SNP) sites in the leptin gene of horses (A326G, C481T, A580G), one SNP site in ghrelin (T176C), one SNP site in cytochrome P450 (T556G), one SNP site in glucocorticoid receptor (T90C), and two SNP sites in lactate dehydrogenase A (A371T, G399T). Body mass index (HT/BW) and body weight for mares who were homozygous guanine at leptin A326G were highest (P < 0.05) of all genotypes identified. Monocytes, as a percentage of white blood cells, were increased (P < 0.05) for mares that were homozygous guanine at T556G. At SNP site A371T homozygous thymine mares were the tallest (P < 0.05) of all genotypes. Results from this study suggest that polymorphisms associated with leptin, ghrelin, cytochrome P450, glucocorticoid receptor and lactate dehydrogenase genes could be used as genetic markers for phenotypic traits in horses as well as indicators of the overall health and wellbeing of the animal. These results indicate a further need for research in this area, which could lead to better recommendations for managing horses with diverse body conditions and could lead to selecting horse with overall increased fitness.