Identification of Single Nucleotide Polymorphisms that Contribute to the Bovine High Androstenedione Phenotype

Authors

Mackenzie Stohlmann, University of Nebraska-LincolnFollow

First Advisor

Andrea S. Cupp

Committee Members

Jennifer Wood, Jessica Petersen

Date of this Version

8-2025

Document Type

Thesis

Citation

A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Animal Science

Under the supervision of Professor Andrea S. Cupp

Lincoln, Nebraska, August 2025

Comments

Copyright 2025, Mackenzie Stohlmann. Used by permission

Abstract

A population of females in the University of Nebraska-Lincoln research herd exhibit naturally occurring androgen excess (androstenedione; A4; High A4) in the follicular fluid of dominant follicles. Previously, a novel single nucleotide polymorphism (SNP) in the Follicle Stimulating Hormone Receptor (FSHR) gene was associated with pubertal classifications and initially with the High A4 phenotype in our herd. We designated this SNP, FSHR SNP2 ((chr11:31404255G>C (rs21971504)). We hypothesized FSHR SNP2 could be used as a marker to identify High A4 cows. To test this hypothesis, we conducted Kompetative Allele Specific PCR (KASP) genotyping on cows with their A4 status classified in 2008-2024 (n = 206) to determine if FSHR SNP2 was associated with the High A4 phenotype. A Chi-square test determined that the alternate FSHR SNP2 did not segregate to the High A4 classification. We then identified heifers born in 2024 (n = 10) which represent all three genotypes (homozygous for the reference allele, heterozygous, and homozygous for the alternate allele) to determine A4 classification and ovarian phenotypic characteristics different between the three genotypes. A Fisher’s test determined that FSHR SNP2 did not segregate to High A4 animals. The androstenedione concentrations in cortex media, nor ovarian phenotypic measures between the three genotypes were not different. There was a tendency for both homozygous groups to have more follicles > 10mm. To determine if we could identify other SNPs contributing to the High A4 phenotype, we utilized a Genome Wide Association Study (GWAS) using SNP chip data in animals with an existing A4 classification (n = 248). There were no SNPs that reached the statistically significant threshold (p < 5×10^-8). While FSHR SNP2 was not found to be a marker for the A4 classification, we demonstrated that High A4 cows tended and High A4 heifers had more surface antral ovarian follicles compared to controls. Furthermore, High A4 heifers had greater numbers of follicles < 7mm on their ovaries compared to controls. No significant SNPs were found in our GWAS analysis to contribute to the High A4 phenotype, however, we have a foundational data set for determining potential SNPs that contribute to the excess A4 phenotype in future studies.

Advisor: Andrea S. Cupp