Superovulation of dairy cows using recombinant FSH (bscrFSH): Effect of the number of FSH applications on ovarian response, hormone profiles, and in vivo embryo production.

The application of bovine single-chain recombinant follicle stimulating hormone (bscrFSH) for developing new superovulation (SOV) protocols with a reduced number of FSH applications was tested in lactating dairy cows with the aim of reducing animal welfare concerns and lowering labour requirements. Embryo donor cows were randomly divided into two experimental groups (n = 12 each) to undergo two different SOV protocols: a) SOV protocol using four bscrFSH applications (one dose/day, 24 h apart, four consecutive days; total: four decreasing doses), and b) SOV protocol using two bscrFSH applications (one dose/day, 48 h apart, two alternate days; total: two decreasing doses) to determine their potential effects on superovulatory response, circulating hormone levels, and in vivo embryo production. Circulating 17β-estradiol, FSH, LH, and progesterone concentrations were unaffected over time by bscrFSH treatment, irrespective of the SOV protocol used (p > 0.05). The dimension and number of ovarian structures was greatest for cows treated with four bscrFSH applications (ovulatory follicles on Day 8: 14.4 ± 1.2 vs. 12.8 ± 0.9 (p > 0.05); corpora lutea on Day 15: 10.0 ± 0.0 vs. 7.8 ± 0.2 (p < 0.05), for four and two bscrFSH applications, respectively). The number of transferable embryos and total embryos (transferable + degenerated) differed between bscrFSH treatments and was greatest for cows treated with four bscrFSH applications (transferable embryos: 6.0 ± 0.5 vs. 5.2 ± 0.2 (p < 0.05); total embryos: 8.0 ± 0.3 vs. 7.1 ± 0.2 (p < 0.05), for four and two bscrFSH applications, respectively). Moreover, the number of unfertilized oocytes differed between SOV protocols (0.1 ± 0.0 vs. 0.3 ± 0.1 (p < 0.05), for four and two bscrFSH applications, respectively). In conclusion, the treatment using two bscrFSH applications affected the number of corpora lutea, the sum of transferable embryos, and unfertilized oocytes. However, superovulation response can be successfully induced with just two applications of bscrFSH maintaining similar circulating hormone profiles and a reasonable number of in vivo produced embryos compared to cows treated using four applications of bscrFSH.