Date of Graduation


Document Type


Degree Name

Master of Science in Animal Science (MS)

Degree Level



Animal Science


Hayden Brown

Committee Member

Jeremy G. Powell

Second Committee Member

Charles F. Rosenkrans

Third Committee Member

Fred Pohlman


Biological sciences, Fescue, Genotype, Heifers, Lactate dehydrogenase, Prolactin


Objectives of this research were to determine effects of LDH enzymatic activity and circulating PRL on immune response, growth, composition, and reproduction, and to determine the effects of single nucleotide polymorphisms of LDH and PRL on immune function, growth and carcass traits, cyclicty, and fecundity of replacement heifers grazing endophyte infected tall fescue. Eighty-nine Angus based heifers had physical and ultrasound measurements along with blood samples collected at weaning, yearling, and prebreeding. Estrus detection was conducted for 10 d post each collection period, except prebreeding. Pregnancy status was verified after AI and again after bull removal. Heifers were maintained on tall fescue with corn gluten and free choice mineral supplementation. A 48 hr delayed hypersensitivy immune trial was conducted at 10 mo of age. Activity of LDH (forward and reverse) was correlated to: hormonal and enzymatic activities, growth, and carcass traits. Concentrations of PRL were associated with growth responses. Single nucleotide polymorphisms of LDH related to: hormonal and enzymatic activities, growth, carcass, cyclicity and immune responses. Polymorphisms of PRL related to carcass traits, pregnancy status, and MCV of immune response. Canonical correlations found no association between LDH activity or PRL concentration to physical set 1 traits of: body weight, hip height, and hip width, and subsequently no correlation to set 2 traits of: pelvic height, pelvic width, Longissimus dorsi area, and rib fat found in other studies. Environmental impact may have obscured anticipated results. Timing and handling appear to be of consideration to recorded measurements in regards to hormonal and metabolic connections. Growth, carcass, and other hormonal measures taken during the trial correlated amongst each other and immune responses serving as further indicators of visual manifestations recognizing the complexity of endocrine functions.