125 Influence of length of porcine follicle-stimulating hormone (p-FSH) treatment before ovum pickup on ovarian response and in vitro embryo production in Holstein heifers

Ovarian follicle stimulation with exogenous FSH before ovum pickup (OPU) in Bos taurus females is a common practice to increase invitro embryo production (IVP). The optimal stimulatory period length for OPU-IVP, however, has not been definitively ascertained. The objective of the present study, therefore, was to determine the effect of length of the superstimulatory treatment period before OPU on ovarian response and IVP in Holstein heifers. Nonpregnant heifers (n = 57) 13.8 ± 0.2 months of age with moderate body condition score (3.0 ± 0.1; scale 1 to 5) were assigned in a completely randomised design to one of the following experimental groups: FSH2d: 200 mg of p-FSH (Folltropin-V®, Vetoquinol) distributed in four injections (60, 60, 40, and 40 mg) of FSH 12 h apart; FSH3d: 200 mg of p-FSH distributed in six injections (40, 40, 40, 40, 20, and 20 mg) of FSH 12 h apart. Timing of follicular wave emergence was synchronized by dominant follicle removal 36 h before the first p-FSH injection in all heifers. An intravaginal progesterone (P4) implant (1.38 g of P4 CIDR®, Zoetis) was inserted at the time of the first p-FSH injection and removed at the time of OPU, which occurred in all heifers at 44 h (Nivet et al. 2012 Reproduction 143, 165-171; https://doi.org/10.1530/REP-11-0391) after the last p-FSH injection. Additionally, follicle number was determined at OPU and classified as small ( 10 mm). Oocytes from follicles of different sizes were pooled by heifer at OPU and then classified and subjected to IVP procedures. Differences between treatment groups were evaluated using generalized linear mixed models (SAS 9.4; SAS Institute Inc.) and data are presented as mean ± s.e.m. (Table 1). Lengthening the FSH treatment period resulted in a greater (P = 0.01) number of large follicles; however, the number of small, medium-size, and total follicles was not different between groups. Number of total recovered oocytes, viable oocytes, cleaved oocytes, as well as recovery rate, percent viable oocytes, and cleavage rate were not different (P > 0.2) between groups. Similarly, the number of blastocysts produced per heifer and blastocyst rate were not different (P > 0.9) among groups. In conclusion, lengthening the period of FSH treatment by 1 day increased the number of large follicles at OPU but did not improve overall ovarian response, oocyte recovery, or embryo production. Table 1. Ovarian response and IVP of heifers treated with p-FSH during 2 or 3 days before ovum pickup Response FSH2d (n = 28) FSH3d (n = 29) P-value Small follicles (n) 5.9 ± 0.6 5.7 ± 0.8 0.83 Medium follicles (n) 17.0 ± 2.4 12.9 ± 1.6 0.18 Large follicles (n) 2.5 ± 0.5 4.5 ± 0.6 0.01 Total follicles (n) 25.4 ± 2.6 23.1 ± 1.8 0.60 Total oocytes (n) 17.0 ± 2.5 13.0 ± 1.2 0.23 Recovery rate (%) 62.6 ± 3.7 56.9 ± 3.1 0.26 Viable oocytes (n) 14.4 ± 2.0 11.3 ± 1.1 0.30 Viable oocytes (%) 85.0 ± 2.4 88.0 ± 3.0 0.31 Cleaved oocytes (n) 8.7 ± 1.6 7.1 ± 1.2 0.62 Cleavage rate (%) 54.7 ± 5.7 54.1 ± 5.7 0.96 Blastocysts (n) 3.2 ± 0.6 3.2 ± 0.7 0.98 Blastocyst rate (%) 20.6 ± 4.0 22.4 ± 3.7 0.97