Effect of different hormonal combinations on follicular wave emergence and superovulatory response in sheep

The aim of the present study was to compare hormonal treatments to induce and synchronize follicular wave emergence to improve the results of superovulatory (SOV) treatments in ewes. In Experiment 1 (n = 66), ewes were treated with a progesterone intravaginal implant plus a PGF_2α analogue (group G_P4), or with the same treatment plus estradiol benzoate (G_P4+EB), a GnRH agonist (G_P4+GnRH), or both, estradiol benzoate and a GnRH agonist (G_P4+EB+GnRH) in a 2 × 2 factorial arrangement. Follicular wave emergence was determined by ultrasound. Follicular wave did not emerge during the studied period in 10 females (one from G_P4, six from G_P4+EB and three from G_P4+EB+GnRH). Follicular emergence was less synchronized (P = 0.007) when estradiol was administered (G_P4+EB: 103.6 ± 22.0 h), without any interaction with GnRH treatment (G_P4+EB+GnRH: 80.1 ± 21.4 h, G_P4+GnRH: 52.5 ± 8.7 h, G_P4: 56.6 ± 10.4 h). Estradiol administration delayed the moment of follicular emergence (P = 0.007) and the follicular wave emergence moment in which follicular dominance was achieved (P = 0.009), without interactions between estradiol and GnRH in the moment of follicular wave emergence or dominance. In Experiment 2 (n = 22), two SOV protocols were compared: the best treatment of Experiment 1 (G_P4) was used to synchronize follicular wave emergence, initiating the SOV treatment 2.5 days later; in the control treatment, SOV treatment started 80 h after a short-term protocol to synchronize ovulation (G_control). The number of corpora lutea (CL) and the evaluation of the collected embryos were performed six days after estrus. Blood samples were collected daily for plasma progesterone determination. Although the number of CL was similar in G_control (7.1 ± 1.0) and G_P4 (6.9 ± 5.1), the number of structures and viable embryos recovered were greater in G_control (P < 0.05). The occurrence of luteal premature regression was significantly greater in G_P4 (60%) than in G_control (8.3%). The use of GnRH agonist alone did not improve synchronization of follicular wave emergence. When EB was used (alone or associated) follicular wave emergence was less synchronized. The SOV protocol proposed had a similar ovarian response; however, it resulted in less transferable embryos.