Effect of use and dosage of p-follicle-stimulating hormone for ovarian superstimulation before ovum pick-up and in vitro embryo production in pregnant Holstein heifers.

The benefit of ovarian superstimulation using exogenous FSH before ovum pick-up (OPU) and in vitro embryo production (IVEP) has been the subject of conflicting results. The objective of the present study, therefore, was to evaluate the effect of use and dose of porcine FSH (p-FSH) before OPU/IVEP on ovarian response and embryo production in pregnant heifers. Pregnant Holstein heifers (n = 48) were randomly assigned to receive 0, 160, or 300 mg NIH-FSH-P1 in a crossover design. Ovum pick-up was performed at 49, 63, and 77 d of gestation with a 14 d "washout" between OPU sessions. Follicle ablation was performed on D 0 (p.m.) and p-FSH treatments, consisting of 4 decreasing dose injections administered 12 h apart, were initiated 36 h after follicle ablation (d 2 a.m.). Heifers underwent OPU on D 5 (a.m.), 40 h after the last p-FSH treatment, and cumulus oocyte complexes (COC) were subjected to IVEP procedures. Differences between treatment groups were evaluated using generalized linear mixed models. There were quadratic effects of treatment on both number and percentage of small (<6 mm), medium (6-10 mm), and large (>10 mm) follicles. Number and percentage of medium follicles increased with increasing p-FSH dosages, although the magnitude of the change was greater between 0 and 160 mg, than between 160 and 300 mg of p-FSH. Total number of follicles, number of COC recovered and number of viable COC increased linearly with increasing p-FSH dose. Conversely, there was no evidence for an effect of p-FSH dose on COC recovery percentage nor the percentage of viable COC. Cleavage percentage, number of cleaved oocytes, blastocyst percentage, and number of blastocysts increased linearly with increasing p-FSH dose. In conclusion, use of p-FSH before OPU resulted in greater superstimulatory response and oocyte competence which in turn increased IVEP. Furthermore, these effects were dose dependent such that use of a greater dose of p-FSH up to 300 mg progressively increased embryo yield.