Ovulatory response to GNRH agonist during early and late fall in mares

This study aimed to assess the ovulatory response of deslorelin acetate during the fall and the response to PGF2α 8 d post-ovulation. One hundred estrous cycles from 22 mares kept in 40o latitude were evaluated. Mares were checked by transrectal ultrasonography until a preovulatory follicle was detected and ovulation induced with deslorelin acetate. Ovulation was confirmed by ultrasonography performed at 24, 36 h post-induction and then repeated at 2-h intervals post-induction. Serum progesterone concentrations and luteal tissue area were determined daily to assess CL function. A dose of PGF2α was administered 8 d post-ovulation and interval to the subsequent ovulation was observed. Each mare repeated this cycle up to five times. The effects of local climate on endpoints were analyzed. Cycles were grouped as early (Sept. 13, 2020-Oct. 31, 2020; n=55) and late fall (Nov. 1, 2020- Dec. 31, 2020; n=45) based on the date of induction. The overall number of mare responding to deslorelin with ovulations between 24-48 h was 90%. Multiple ovulations were similar between early (n=5) and late (n=4) fall (P=0.87). There were no differences in spontaneous ovulations occurring before 24 h between early (n=6) and late (n=2) fall (P=0.29). Two failures to respond to deslorelin by 48 h were recorded in early fall and none in the late fall. The interval from induction to ovulation was similar in early (40.6±0.4 h) and late (41.2±0.5 h) fall (P=0.55). The percentage of mares ovulating between 36 and 48 h post-deslorelin did not vary between early and late fall (91 vs. 95 %, P=0.21), as did ovulation occurring between 38 h and 44 h (62 vs. 60%, P=0.69). Follicle size at induction tended to be smaller in early (36.4±0.4mm) than late (37.4±0.4mm) fall (P=0.07). Edema scores varied with time relative to ovulation (P<0.001) and were lower in late fall (P=0.01). Progesterone concentrations varied with time (P<0.001) but did not differ between early and late fall (P=0.73) and correlated weakly with the luteal area (r=0.13; P=0.031). Follicles < 35mm at the PGF2α had a shorter interval to the next ovulation than follicles ≥35mm (9.2±0.5 d vs. 10.6 ± 1.2 d) (P=0.03). Lower temperature led to a smaller follicle size at induction (P=0.0021) and ovulation (P=0.009) and lower relative humidity yielded a larger follicle size at ovulation (P=0.032). In conclusion, cycling mares displayed a highly efficacious response to deslorelin acetate and apparently normal luteal function during the fall, despite lower edema scores in late fall.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

VMS-Veterinary Clinical Medcne

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Spencer, Kianna M.

Contributors dc:contributor

• Canisso, Igor F
• Marshall, Tessa S
• Shipley, Clifford F
• Garrett, Edgar F

• ovulation
• deslorelin acetate
• progesterone
• luteal function

Statement dc:rights

• Copyright 2022 Kianna Spencer

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/115787

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F115787