Weaned Sows with Small Ovarian Follicles Respond Poorly to the GnRH Agonist Buserelin

Abstract

The GnRH agonist buserelin (GnRH), used to synchronize ovulation in weaned sows, attains only 70–80% effectivity, owing to several reasons of ovarian origin. This study evaluated in particular whether mean ovarian follicle size at treatment and the season of weaning are among those influencing GnRH responsiveness. The experiment was carried out in a temperate-region farm with 352 sows of 1–6 parities weaned either in winter–spring (WS, 174 sows) or in summer–autumn (SA, 178 sows). The sows were randomized into two groups: GnRH (10 µg of buserelin acetate at 86 h after weaning, 172 sows) and control (180 sows). The ovaries were transrectally scanned from weaning to ovulation and the sows clustered according to their mean follicular size at treatment time: small (<0.5 cm in diameter), medium (0.5 to 0.64 cm) and large (0.65 to 1.09 cm). In total, 88.33% of the GnRH-treated sows ovulated, with 82% of them within the expected time window (120–132 h after weaning). In contrast, 95.45% of the unresponsive sows had small follicles at the time of treatment and were mostly weaned in SA (20.45%) than in WS (4.76%). In conclusion, the conspicuous presence of sows having small ovarian follicles at treatment time compromises the efficiency of the GnRH agonist buserelin to synchronize ovulation in weaned sows, which occurs more frequently in summer–autumn weaning.

GnRH-mediated suppression of S100A4 expression inhibits endometrial epithelial cell proliferation in sheep via GNAI2/MAPK signaling

“…In summary, GnRH participates in the embryo implantation process by mediating various functions of endometrial cells, and exogenous GnRH can affect uterine function. Therefore, GnRH is often used clinically to induce ovulation during superovulation (9)(10)(11) and to synchronize estrus (12,13).…”

“…GnRH is widely used to increase pregnancy rates in sheep. GnRH agonists/antagonists were first used to control follicle development (9)(10)(11)14) and to assess the efficacy of estrus induction during different periods (15). This molecule can also be used to induce estrus synchronization (12,13,16).…”

Application of Exogenous GnRH in Food Animal Production

“…Similar to eCG, optimal GnRH dosages for inducing an ovulatory LH surge are product-dependent, being 10 µg for buserelin [19], 50 µg for gonavet [20], 10 µg fertilan [20], 25 µg for lecirelin [21], and 100-200 µg for intravaginal triptorelin [22][23][24][25][26][27]. Additionally, the efficacy of GnRH for ovulation induction is influenced by follicle size with sows having smaller follicles (<6.5 mm; [28]; <5.0 mm; [29]) at the time of treatment having poorer ovulation responses, presumably reflecting follicular immaturity.…”

GnRH agonists: Updating fixed‐time artificial insemination protocols in sows

“…They have a prolonged half‐life, which makes them more efficient than endogenous GnRH (Fries et al, 2010). The agonist's design is intended to stabilize the molecule against enzymatic attack, increase its binding to plasma proteins and membranes, and increase its affinity to the GnRH receptor (Lopes et al, 2020). In swine production, GnRH agonists are used for ovulation induction afterestrus synchronization by altrenogest (15–20 mg/day/sow for 14–18 days) in gilts or weaned multiparous sows to achieve an additional synchronization effect that can be used to fulfil FTAI protocols (Kirkwood & Kauffold, 2015).…”

“…In some later studies, buserelin was administered at different times (24, 77, 94, and 104 h after weaning) and at different doses (6, 10, 16, 16, and 50 μg) (Driancourt et al, 2013; Martinat‐Botté et al, 2010; Wongkaweewit et al, 2012). Currently, the recommendation for multiparous sows is an intramuscular injection of 10 μg buserelin 83–89 h after weaning and a single insemination 30 to 33 h later, with ovulation occurring 42 ± 2 h post‐buserelin (Baroncello et al, 2017; Falceto et al, 2014; Lopes et al, 2020; Pearodwong et al, 2019).…”