226 Using a long-acting recombinant human follicle-stimulating hormone in cattle: 2. Superovulatory response

In a previous study, we demonstrated that long-acting human recombinant follicle-stimulating hormone (rhFSH) can be used to stimulate follicle growth in cattle. The aim of this study was to evaluate the superovulatory response to this rhFSH. Cycling Nelore heifers (n = 19) with an average 371.7 ± 5.7 kg bodyweight were subjected to a follicular wave synchronization protocol consisting of the insertion of an intravaginal progesterone-releasing device (1 g, Sincrogest, Ouro Fino, Brazil) and 2 mg of oestradiol benzoate (Sincrodiol, Ouro Fino) on Day −4, and were superovulated (Day 0) either using eight decreasing doses 12 h apart of pFSH (120 mg Folltropin-V, Vetoquinol, Brazil, n = 9) or with a single subcutaneous injection of 20 µg rhFSH (Corifollitropin Alpha, Shering-Plough, Brazil, n = 10). On Day 3 the progesterone (P₄) devices were removed and luteolysis was induced with 26.3 mg cloprostenol sodium (Induscio, GlobalGen, Brazil). On Day 4, ovaries were scanned using an ultrasound equipped with a 7.5-MHz rectal probe (DP 30, Mindray, Brazil) and follicles were measured and classified according to diameter. On Day 5 ovulation was induced with 16 µg buserelin acetate (Maxrelin, GlobalGen) and heifers were inseminated twice, immediately after ovulation induction and 12 h later, with semen from a single Nelore sire. Seven days after the first AI, the number of corpora lutea (CL) was counted by ultrasound, blood samples were collected for P₄ analysis, uterine flushing was carried out, and the number of ova and viable embryos recorded. Plasma P₄ concentrations were evaluated by electrochemiluminescence (Immulite P₄, Siemens, UK). Data were analysed using the Proc Glimmix of SAS. There was no difference in the number of follicles <4 mm (2.4 ± 0.6 vs 1.6 ± 0.5; P = 0.3017), from 5 to 6 mm (7.9 ± 1.1 vs 7.1 ± 0.8; P = 0.5780) or >7 mm (24.3 ± 4.3 vs 30.0 ± 5.1; P = 0.44) on Day 4 between groups pFSH and rhFSH, respectively. Plasma P₄ concentrations on the day of embryo flushing did not differ between pFSH and rhFSH groups (54.4 ± 14.6 vs 66.5 ± 10.4 ng mL⁻¹, respectively; P = 0.50). However, heifers receiving rhFSH presented greater mean follicle size on Day 4 (8.6 ± 0.1 vs 8.0 ± 0.1; P < 0.01), ovulation rate (61.3% vs 42.5%, P < 0.01), and number of CL (18.4 ± 2.5 vs 10.3 ± 1.6; P < 0.05), and a trend towards more ova (8.3 ± 1.4 vs 5.1 ± 0.9; P = 0.07) and viable embryos (2.5 ± 0.9 vs 0.6 ± 0.3; P = 0.06), when compared with those receiving pFSH. In summary, superovulation can be successfully induced in Nelore heifers with a single dose of a long-acting rhFSH.

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