Effect of gonadotrophin dose on oocyte retrieval in superovulated BALB/c mice

Mice are commonly used animal models in reproductive and developmental research. In order to get satisfying results from such experiments, large numbers of ova must be available and this can be achieved by using various ovulation induction protocols. To obtain an optimal response from these stimulation protocols, parameters such as breeding-housing conditions of the animal strains, the best age for superovulation, and type and dose of gonadotrophins must be optimized. The aim of this study was to investigate the impact of exogenous stimulation with increasing amounts of gonadotrophins on the number and quality of oocytes/pre-embryos recovered from outbred BALB/c mice. A dose-response analysis was performed by stimulating prepubescent (21- to 25-day-old) and sexually mature (6 to 8 weeks old) female mice with hMG, which contains equal amounts of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The stimulation dose contained 5, 10, 15, 20, 25 or 30 IU of FSH/LH. The effect of increasing stimulation was assessed by monitoring the number and maturity of ova recovered from the tubes. The data were analyzed by using a one-way Anova test and student t-test. Increasing stimulation doses in the prepubescent females resulted in an increased number of ova. A maximum of 55 ova per mouse was reached when stimulating with 20 IU of FSH/LH; higher stimulation doses showed no further increase in oocyte recovery. In the prepubescent group, a maximal number of recovered mature ova was reached with 15 IU of FSH/LH. In the sexually mature female group, 20 IU of FSH/LH gave the best quantitative and qualitative results. Positive effects of copulation on the number and maturity of oocytes in all induction doses were more evident in the prepubescent females and these parameters were significantly more improved (P < 0.05) in this group when compared to the pubertal females. Our findings led to the conclusion that ovulation induction of prepubescent outbred BALB/c mice with 15 IU FSH/LH and sexually mature ones with 20 IU FSH/LH give the best results in terms of oocyte number and maturity.