Semester of Graduation

Summer 2026

Degree

Master of Science (MS)

Department

Animal Science

Document Type

Thesis

Abstract

Mares entering seasonal anovulation during winter present a significant challenge for equine breeding programs. Treatment with estradiol cypionate (ECP) and sulpiride in a long-acting vehicle can advance the first ovulation of the season; however, the molecular and secretory mechanisms underlying this response remain unclear. This study compared follicle wall gene expression and endocrine factors (from blood plasma and follicular fluid) among seasonally anovulatory mares responding to ECP-sulpiride (RESP; n = 15, treated with 50 mg ECP and 3 g sulpiride), mares undergoing natural spring transition (ST; n = 16, vehicle-treated only), and mares cycling during the summer ovulatory season (SOV; n = 10, untreated). Follicle wall biopsies and follicular fluid were collected when a follicle was ≥ 32 mm in all groups. Plasma prolactin (PRL) and luteinizing hormone (LH) were measured daily following treatment, intrafollicular PRL, vascular endothelial growth factor A (VEGFA), progesterone, and estradiol were quantified, and follicle wall expression of LH receptor (LHr), VEGFA, and VEGF receptor 1 (FLT1) was assessed by qPCR. Of 20 seasonally anovulatory mares treated with ECP-sulpiride, 15 mares responded with a ≥ 32 mm follicle within 15 days of treatment (RESP group). The RESP mares had increased plasma PRL and LH compared with ST mares (P < 0.05 and P < 0.01, respectively), with PRL remaining elevated for 9 days post-treatment. Intrafollicular PRL and VEGFA concentrations were greater in RESP than ST mares (P < 0.001 for both), with no differences detected between RESP and SOV. Progesterone and estradiol did not differ among groups. Intrafollicular PRL was positively associated with VEGFA (Spearman’s ρ = 0.73; P < 0.0001). Post-hoc covariate analysis revealed diameter-dependent VEGFA expression in RESP follicles, with FLT1 showing a weaker similar pattern; however, group means for LHr, VEGFA, or FLT1 expression did not differ. These associations were not observed in SOV or ST follicles. These findings indicate that ECP-sulpiride treatment elevates systemic PRL and LH and enhances intrafollicular PRL and VEGFA concentrations to those comparable with naturally cycling mares. Diameter-dependent VEGFA expression in RESP follicles suggests PRL-linked modulation of angiogenic signaling during pharmacologically induced follicular recrudescence.

Date

7-17-2026

Committee Chair

Oberhaus, Erin

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

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