Ovarian follicular growth suppression by long-term treatment with a GnRH agonist and impact on small follicle number, oocyte yield, and in vitro embryo production in Zebu beef cows

Abstract

The aim of the present study was to evaluate small follicle number, oocyte yield, and in vitro embryo production (IVEP) in Zebu beef cows treated long term with a GnRH agonist to suppress ovarian follicular growth. Nelore (Bos indicus) cows (n = 20) showing regular estrous cycles were randomly assigned to one of two groups: control (n = 10, placebo ear implant without a GnRH agonist); GnRH agonist (n = 10, GnRH agonist ear implant containing 9.4-mg deslorelin). All cows underwent an ovum pick-up (OPU) session 14 days (Day 14) before the start of treatments (Day 0) followed by seven OPU-IVEP procedures at 30-day intervals (Days 0, 30, 60, 90, 120, 150, and 180). Semen from a single batch of a previously tested bull was used for all the IVEP. Cows treated with agonist reported a decrease over time in the proportion of animals with a (CL; P ≤ 0.05) and large follicles (>10 mm, P ≤ 0.05). These cows had a lesser number of medium + large follicles (>5 mm; 1.74 ± 0.5 vs. 4.13 ± 0.5; P ≤ 0.05), greater number of small follicles (2-5 mm; 44.3 ± 2.8 vs. 30.8 ± 1.8; P ≤ 0.05), greater yield of cumulus-oocyte complexes (COCs; 21.0 ± 2.3 vs. 15.6 ± 1.9; P ≤ 0.05), greater proportion of COCs cultured (79.2 vs. 73.9%; P ≤ 0.05), COCs cleaved (10.6 ± 1.5 vs. 6.8 ± 1.1, P ≤ 0.05), and cleaved rate (52.8 vs. 44.3%; P ≤ 0.05) compared with control cows. The number (3.4 ± 0.7 vs. 3.0 ± 0.6; P > 0.05) and proportion (16.5 vs. 19.1%; P > 0.05) of blastocysts produced were similar between agonist and control cows, respectively. The study has shown that Zebu beef cows treated long term with a GnRH agonist had follicular growth restricted to small follicles. This did not compromise the ability of oocytes to undergo IVF and embryonic development.

Deslorelin Slow-Release Implants Delay Ovulation and Increase Plasma AMH Concentration and Small Antral Follicles in Haflinger Mares

“…Altogether, the effects of deslorelin SRI on the population of small antral follicles may recommend this treatment as a possible approach for the preparation of mares for OPU. In Zebu beef cows, treatment with deslorelin SRI resulted in effects on small follicles similar as in the mares of the present study for up to 180 days and allowed for the aspiration of a higher number of follicles via OPU [35]. In horses, the number of recovered oocytes after the OPU procedure is one of the most important factors for the successful application of ICSI [36].…”

“…It may be the aim of future studies to determine if deslorelin SRI treatment might also improve the oocyte yield in aged mares with low AFC [36]. In Zebu cows, the increased number of aspirated follicles after deslorelin SRI treatment was not associated with increased oocyte recovery rates [35]. Detrimental effects of the prolonged absence of luteal tissue and an associated increased LH pulse frequency have been suggested as the underlying cause [39].…”

Intraovarian injection of mesenchymal stem cells improves oocyte yield and in vitro embryo production in a bovine model of fertility loss

“…In Experiment 2, most donors had varied records of chronic COD and refractoriness to conventional GnRH or P4 treatments, so they were treated with an anti-GnRH vaccine. Previous studies have shown that cows receiving either GnRH immunization or GnRH agonist, despite having suppressed follicle growth, can be used as oocyte donors and produce embryos in vitro 14,48 . Therefore, we decided to include a group with FSH priming, and thus we could not use the same experimental model as in Experiment 1.…”

Factors that interfere with oocyte quality for in vitro production of cattle embryos: effects of different developmental & reproductive stages

“…Focus has been given to the possible positive effects of circulating levels of P4 in determining oocyte quality in IVP (Lonergan, 2011). However, a recent study from our research group has demonstrated that neither exposure to lower levels of LH, nor cycles of P4, are limiting to oocyte viability and development to blastocyst stage (Batista et al, 2016b). Further research is needed to elucidate some of these rather complex interactions between reproductive hormones and oocyte quality.…”