Effects of superstimulation with fsh on follicular population and recovery rate of oocytes in the growing phase of the first and second follicular wave

Effectiveness of in vitro production of embryos (IVP) is limited among other factors by the recovery rate of oocytes. Gonadotropin superstimulation can improve the recovery rate of oocytes. The effect of FSH treatment on follicular population and recovery rate of oocytes at ovum pick-up (OPU) in the growing phase of the 1st as well as the 2nd follicular wave after superstimulation was the object of our experiment. Twelve unpregnant milking cows (15-20 kg milk per day) housed on a dairy farm were used in the experiment. The cows bearing corpus luteum were synchronized by PGF2 (day 0) and they were treated by FSH (Folicotropin inj. sicc. ad us vet., Spofa Prague, Czech Republic, single doses 80, 80, 80, 80, 40 and 40 UI) in 12 h intervals on days 12, 13 and 14. Transvaginal ultrasonographic puncture of oocytes in cows bearing a new corpus luteum was performed on day 7 (OPU 1, various phase of the follicular wave, removal of the dominant follicle) and it was repeated on days 10 (OPU 2, growing phase of the follicular wave - control), 16 (OPU 3, growing phase of the first follicular wave after superstimulation) and 20 (OPU 4, growing phase of the second follicular wave after superstimulation). All follicles > 2 mm were punctured. The ovarian follicles (ultrasonographically) and numbers and qualities of obtained oocytes (microscopically) were evaluated during and immediately after OPU. Follicular population was divided to small (FS, 2-5 mm), medium (FM, 5-9 mm) and large (FL, > 9 mm) follicles. Oocytes were classified as 1st (intact cumulus, > 3 layers of cumulus cells), 2nd (complete 1-3 layers of cumulus cells), 3rd (incomplete layers of cumulus cells, expanded cumulus mass) and 4th (absence of corona cells, degenerated oocytes) classes. Although we found the least of FS (x = 1.0) during OPU 3, significantly more FM (x = 24.7) and FL (x = 3.1) follicles were found at this procedure in comparison with others. Likewise a significantly higher number of oocytes (x = 8.1) was obtained at OPU 3 in comparison with OPU 1 and OPU 2. Significantly higher number of FM (x = 6.1) was found and non-significantly higher number of oocytes was obtained at OPU 4 in comparison with OPU 1 and 2. The results show that administration of FSH increases the number of follicles and the number of collected oocytes in the growing phase of the 1st follicular wave after superstimulation, nevertheless a higher number of follicles and a higher recovery rate of oocytes can be expected in the growing phase of the 2nd follicular wave after superstimulation as well.