71 Effect of follicle-stimulating hormone dose and circulating progesterone before ovum pickup and invitro embryo production in pregnant Holstein heifers

Superstimulation with exogenous FSH before ovum pickup for invitro embryo production (IVP) improves embryo production. However, there is limited information on different FSH dose regimens and the effect of progesterone (P4) concentrations on IVP. Thus, the objective of the present study was to evaluate the effect of FSH dose and circulating P4 on ovarian superstimulation responses, before ovum pickup (OPU) on IVP in pregnant heifers. Pregnant Holstein heifers (n=47) 19.5±0.3 months of age with moderate body condition score (3.3±0.03; scale 1 to 5) were randomly assigned to 2 treatment groups, p-FSH (Folltropin-V, Vetoquinol) 160mg (FSH160) or p-FSH 300mg (FSH300), in a crossover design. Two sessions of OPU were performed on each animal at 48 and 62 days of gestation, with a washout interval between sessions of 14 days. Dominant follicle removal (DFR) was utilised to synchronize follicular wave emergence, and FSH treatments were initiated 36h later. Heifers in both groups received a total of 4 FSH injections 12h apart as follows: FSH160 (48.0, 42.7, 37.3, and 32.0mg) or FSH300 (90.0, 80.0, 70.0, and 60.0mg). All heifers underwent OPU 40h after the last FSH treatment. Blood samples were collected for P4 quantitation at OPU and number of small (<6mm), medium (6–10mm), and large (>10mm) follicles were determined before OPU. Cumulus–oocyte complexes (COCs) recovered were processed and invitro embryo production was performed using standard procedures. Differences between treatment groups were evaluated using generalized linear mixed models, and data are presented as mean±s.e.m. (Table 1). Heifers treated with 300mg of p-FSH had a greater (P<0.05) number of medium-size follicles, total number of follicles, total COCs recovered, number of viable COCs, and number of blastocysts produced. In addition, heifers treated with 300mg of p-FSH had a greater cleavage rate (P=0.03). Circulating P4 was on average 10.1±0.4ng mL−1 and did not differ between gestation days (P=0.12). Furthermore, circulating P4 did not affect (P>0.10) any of the outcomes evaluated, nor was there an FSH dose by circulating P4 interaction (P>0.05). In conclusion, increasing the dose of p-FSH before OPU from 160 to 300mg resulted in an increase in the total number of follicles, number of oocytes, and number of blastocysts produced in pregnant donors without changes in blastocyst rate, regardless of progesterone concentrations at the time of OPU. Table 1. Ovum pickup and invitro embryo production in pregnant heifers treated with different doses of p-FSH Item FSH160 FSH300 P-value Small follicles (n) 5.0±0.6 3.5±0.4 0.02 Medium follicles (n) 14.4±0.8 18.3±0.9 0.0003 Large follicles (n) 2.9±0.3 2.5±0.3 0.28 Total follicles (n) 22.3±0.7 24.3±0.9 0.04 Total oocytes (n) 12.8±0.7 14.7±1.0 0.02 Recovery rate (%) 56.2±2.1 59.7±2.7 0.20 Viable oocytes (n) 11.4±0.7 13.3±1.0 0.02 Viable oocytes (%) 89.9±1.7 88.0±2.4 0.22 Cleavage rate (%) 63.8±4.3 71.5±3.7 0.03 Cleaved oocytes (n) 7.2±0.7 9.3±0.9 0.14 Blastocysts (n) 2.7±0.4 3.6±0.7 0.02 Blastocyst rate (%) 22.0±3.3 22.4±3.6 0.74