225 Using a long-acting recombinant human follicle-stimulating hormone in cattle: 1. Superestimulatory response

The aim of this study was to evaluate the superestimulatory response of cattle to a long-acting recombinant human follicle-stimulating hormone (rhFSH). Pubertal Nelore (Bos taurus indicus) heifers weighing 517.5 ± 10.6 kg were used. All heifers were submitted to a follicular wave suppression protocol, consisting of two subcutaneous (SC) injections of an anti-GnRH vaccine (Bopriva, Zoetis, Brazil) given 20 days apart, and only those without follicles >4 mm 2 weeks after the second (boost) injection were used. The first experiment consisted of a dose–response study. Heifers (n = 20) were allocated into one of five groups, which received placebo (saline) or a single SC dose of 7.5, 15.0, 22.5 or 30.0 µg of rhFSH (Corifollitropin Alpha, Shering-Plough, Brazil) on Day 0. Blood samples were collected and follicle dynamics evaluated by ultrasonography (MyLab 30 Vet Gold, Esaote, Italy) daily, for 12 days. All visible follicles present in the ovaries were measured. Serum FSH concentrations were evaluated by electrochemiluminescence (Immulite FSH, Siemens, UK). Data were analysed using the Proc Glimmix of the SAS with a repeated-measurement statement. As expected, there were group, time, and group × time effects (P < 0.0001) for both mean follicle size and FSH concentrations. The FSH peak concentration on Day 1 and area under curve were similar (P > 0.05) between groups 15.0, 22.5, and 30.0 µg. However, from Day 3 onward, mean follicle size was similar (P > 0.05) between 22.5 and 30.0 µg, but greater (P < 0.01) than for all other doses. The maximum follicle size in groups 22.5 and 30.0 µg was reached on Day 7 (9.3 ± 0.9 and 8.9 ± 1.3 mm, respectively). In a second experiment, Nelore heifers (n = 18) were allocated into one of three groups, which received on Day 0 either placebo (control group), a single SC injection of 25 µg rhFSH, or 130 mg pFSH (Folltropin-V, Vetoquinol, Brazil) given in eight decreasing doses every 12 h. Follicle dynamics was monitored daily by ultrasound for 6 days. On Day 5, samples of follicular fluid were collected by transvaginal ultrasound-guided follicle aspiration and stored at −80°C for further oestradiol (E₂) analysis. Luteinization was then induced with hCG (Chorulon, MSD, Brazil), and 7 days later (Day 12), blood samples were collected for plasma progesterone (P₄) analysis. Intrafollicular E₂ and plasma P₄ concentrations were evaluated by RIA. There was no difference (P > 0.05) in mean follicle size at any moment between groups rhFSH and pFSH, and both differed (P < 0.0001) from control group from Day 1 onward. Follicle growth rate did not differ between rhFSH and pFSH groups, but was greater than in control (1.2 ± 0.1 and 1.3 ± 0.2 vs 0.0 ± 0.0 mm day⁻¹, respectively; P > 0.05). There was no difference in intrafollicular E₂ on Day 5 or in plasma P₄ on Day 12 between groups rhFSH and pFSH (42.0 ± 12.0 vs 33.2 ± 14.2 ng mL⁻¹ and 57.5 ± 21.8 vs 53.7 ± 18.2 ng mL⁻¹, respectively; P > 0.05). In summary, a superstimulatory treatment with a single SC injection of 22.5 to 30.0 µg of a long-acting rhFSH results in a pattern of follicle development, follicular steroidogenesis, and response to luteinization similar to those achieved with the standard protocols using pFSH.

Research was supported by CAPES, DPG UnB, and FAPDF 00193–00002307/2022–11.