ENDOCRINE HORMONE PROFILES AND OVARIAN MORPHOLOGY AS MARKERS OF PUBERTAL STATUS AND FERTILITY IN HEIFERS

Two studies were conducted to determine: 1) endocrine profiles during puberty attainment to predict populations of females that may develop irregular estrous cycles, altered endocrine hormone secretion affecting reproductive performance; 2) whether theca cells from heifers with High or Low antral follicles counts (AFC) had altered VEGFA signal transduction which may predict changes in angiogenesis and follicle development affecting antral follicle size and fertility. We previously identified a population of cows with increased androgens in follicular fluid (High A4), which has reduced SHBG in plasma and displays irregular cycles. High A4 females attain puberty 45 days earlier than control cows. Further investigation into this phenotype led to a three year study to characterize pubertal onset in heifers of the UNL Physiology herd. We hypothesized that heifers with earlier puberty may be predisposed to aberrant endocrine profiles and abnormal cyclicity due to inappropriate establishment of the hypothalamic-pituitary-gonadal axis, resulting in reduced fertility. Study 1 culminated in the discovery of four classifications of heifers depending on pubertal onset (Early, Typical, Start-Stop and Non-Cycling). Progesterone was reduced in Start-Stop and Non-Cycling females when compared with Early and Typical females. Furthermore, SHBG was reduced in the Start-Stop females in comparison to the Early females. Start-Stop heifers identified in this study may become the High A4 females of the herd as mature cows. In study 2, theca cells from High AFC and Low AFC heifers were analyzed for differential expression in VEGFA signal transduction. High antral follicle counts are indicative of a larger ovarian reserve and increased fertility. Preliminary analyses revealed decreased expression of genes in the VEGFA signaling pathway, and increased instances of apoptosis and cell death in the theca cells of the High AFC heifers. This study is ongoing, in an effort to investigate the molecular mechanisms and gene networks that play central roles in establishment of the ovarian reserve and formation of antral follicles, which both are reliable predictors of a young female’s reproductive potential. Advisors: Andrea S. Cupp and Robert A. Cushma