Embryo production by Holstein heifers superovulated with a recombinant long-acting follicle stimulating hormone analog

Abstract This study aimed to evaluate embryo yield in Holstein heifers superovulated with a single injection of recombinant, long-acting human follicle-stimulating hormone (rFSH) vs. multiple injections of pituitary-derived follicle-stimulating hormone (FSH). In experiment 1, heifers were assigned randomly to one of four experimental groups: Control (280 mg of pituitary-derived FSH; six injections of 40 mg and two injections of 20 mg, each ~12 h apart, n = 16); rFSH1 (50 µg of FSH analog protein, n = 16); rFSH2 (75 µg of FSH analog protein, n = 16); or rFSH3 (100 µg of FSH analog protein, n = 16). The rFSH was administered as a single injection. Estrous cycles were presynchronized with gonadorelin acetate (GnRH) and an intravaginal progesterone insert (CIDR) on day 8, followed by cloprostenol sodium (PGF2α) on day 3 and day 2 with removal of the CIDR, and GnRH on day 0. On day 5, ovarian follicles ≥ 5 mm in diameter were ablated by transvaginal ultrasound-guided aspiration. On day 6.5, the heifers received a CIDR and the first injection of either rFSH or pituitary-derived FSH. On day 9, the heifers received two injections of PGF2α, 12 h apart. On day 10.5, the CIDR was removed, and on day 11, the heifers received a GnRH injection. Heifers were AI-inseminated 12- and 24-h post-GnRH injection, and uterine contents were flushed transcervically on day 18 (7 d after the GnRH injection). Ovarian follicles ≥ 5 mm and corpora lutea (CL) were counted via ultrasound on days 5, 9, and 18. In experiment 1, group did not affect (P = 0.52) the number of follicles ≥ 5 mm (Control = 15.9 ± 1.2; rFSH1 = 17.5 ± 1.3; rFSH2 = 17.1 ± 1.3; rFHS 3 = 18.6 ± 1.4 follicles) or the number of CL (P = 0.96) on day 9 (Control = 1.1 ± 0.3; rFSH1 = 1.1 ± 0.3; rFSH2 = 1.1 ± 0.3; rFSH3 = 0.9 ± 0.2). Furthermore, there was no effect (P = 0.28) of rFSH dose on freezable embryos (grade 1 and 2 embryos) collected on day 18 (Control = 4.7 ± 1.1; rFSH1 = 4.7 ± 1.2; rFSH2 = 4.4 ± 1.1; rFSH3 = 2.6 ± 0.7 embryos). In experiment 2, Control (n = 8) and rFSH1 (n = 16) groups were repeated in three replicates using the same protocols as experiment 1. Consequently, Results showed that rFSH produced fewer total number of ova/embryos (Control = 9.9 ± 1.5 vs. rFHS1 = 5.9 ± 0.9, P = 0.04) and fewer freezable embryos (Control = 5.3 ± 1.0 vs. rFSH1 = 1.4 ± 0.3, P < 0.01). In conclusion, the single rFSH injection effectively induced superovulation; however, its repeated use reduced embryo production.