Date of Award

December 2019

Document Type


Degree Name

Doctor of Philosophy (PhD)


Animal and Veterinary Sciences

Committee Member

Scott L Pratt

Committee Member

Nathan M Long

Committee Member

Thomas R Scott

Committee Member

William C Bridges


Prolactin (PRL) is a ~22 kDa peptide hormone reported to regulate over 300 distinct biological functions in vertebrates. Tonic inhibition of prolactin (PRL) by dopamine binding to dopamine receptor-type 2 (DRD2) is well established and changes in PRL serum concentration resulting in detrimental effects to male reproductive physiology have been observed. Release and synthesis of PRL may be altered due to a single nucleotide polymorphism (SNPs) in the DRD2 gene. The objective of these studies were to evaluate associations of a previously identified DRD2 SNP to PRL serum concentrations, growth traits, semen quality, and PRL gene expression in beef bulls. Semen quality, growth traits, and serum PRL concentrations were recorded from bulls exposed to a dopamine agonist over a 4-year study. Testis and epididymis were collected from bulls in Year 1 at the end of a 126 d study. Genotyping was performed on genomic DNA from semen samples by restriction fragment length polymorphism (RFLP) and Taqman custom SNP genotyping assays. Genotype was not associated with semen quality, serum PRL concentrations, or growth traits; however, treatment of a dopamine agonist lowered serum PRL concentrations. Immunohistochemistry revealed the presence of DRD2 in testis, epididymis and sperm cells. Prolactin protein expression, assessed by western blotting, indicated presence of PRL protein in only anterior pituitary. Pituitaries were collected from a local abattoir with selection of male posterior pituitaries performed by duplex PCR and Southern blotting methods. Genotyping was performed by RFLP for the DRD2 SNP. Slot blot and densitometry analysis for PRL protein expression was performed on a subset of male pituitaries (n = 92). No association between the DRD2 SNP and PRL protein expression in bovine anterior pituitary was observed. Taken together, these data indicate no DRD2 SNP genotypic effect on growth or semen quality. Further, PRL protein expression was similar across genotype in the anterior pituitary, the main source of PRL synthesis and secretion.



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