Effect of a single administration of FSH delivered in hyaluronic acid on oocyte competence and hormonal concentrations in Italian Mediterranean buffaloes undergoing ovarian stimulation prior to ovum pick-up

This study evaluated the effectiveness of a single intramuscular administration of follicle-stimulating hormone (FSH) dissolved in 1 % hyaluronic acid (HA) for ovarian stimulation in Italian Mediterranean buffaloes (IMB) undergoing ovum pick-up (OPU). The aim was to simplify hormonal protocols, reduce handling stress, and improve oocyte competence. In Experiment 1, multiparous IMB (n = 24) were enrolled in a crossover design comparing the standard six-dose FSH protocol (FSH-6) with a single FSH-HA injection. Transrectal ultrasonography was used to record the number and the size of follicles, in vitro embryo production to assess oocyte developmental competence, and an in-house radioimmunoassay (RIA) method to measure plasma cortisol levels. In Experiment 2, plasma FSH profile during follicular growth was evaluated in IMB (n = 12) subjected to FSH-HA, FSH-6, or no stimulation (control) protocols. The FSH-HA treatment resulted in a higher (P < 0.05) proportion of medium-sized follicles compared to FSH-6 (3.4 ± 2.7 and 2.0 ± 2.3, respectively) as well as a significantly greater number of cleaved oocytes (3.3 ± 0.4 and 2.4 ± 0.4 respectively), although the total embryo yield remained similar (30.1 ± 7.2 and 29. 2 ± 4.5, respectively). Cortisol concentrations increased after OPU in all groups, but the FSH-HA group showed a trend (P < 0.10) toward lower stress levels compared to FSH-6. In Experiment 2, FSH-HA maintained higher plasma FSH concentrations for a longer period, with peak values observed between 30 and 72 h post-administration, suggesting the importance of optimizing the timing of OPU in HA-based protocols.