231 EFFECT OF DIFFERENT EQUINE CHORIONIC GONADOTROPIN CONCENTRATIONS ON IN VITRO-PRODUCED BOVINE EMBRYOS

Abstract

In vitro maturation (IVM) is one of the most challenging steps in the in vitro production of bovine embryos. The IVM medium must provide the necessary conditions for the occurrence of nuclear and cytoplasmic maturation, close to the physiological conditions. The pituitary gonadotropins are essential components for generating competent oocytes; however, whether these hormones (pituitary, placental, or both) are essential and which concentrations should be used are still controversial. Our work aimed to compare the effect of different concentrations of the placental gonadotropin (eCG) in the IVM medium on the in vitro-produced bovine blastocysts. Cumulus–oocyte complexes (n = 1341, grades I and II), obtained from ovaries from an abattoir were selected and distributed into six groups: (1) eCG (4 IU mL^–1; n = 192); (2) eCG (1.5 IU mL^–1; n = 204); (3) eCG (1.3 IU mL^–1; n = 203); (4) eCG (0.15 IU mL^–1; n = 202); (5) eCG (0.015 IU mL^–1; n = 199); (6) control: FSH (0.1 mg mL^–1), LH (50 µg mL^–1), and 10% of fetal calf serum (FCS; n = 341). Medium from groups 1 to 5 also contained LH (50 µg mL^–1) and BSA (6 mg mL^–1). The cumulus–oocyte complexes were matured in TCM-199 for 24 h and were IVF (Day 0) in TALP-IVF for 22 to 24 h. Viable spermatozoa were selected by Percoll gradient, and they were evaluated (motility and spermatozoa concentration) to provide the insemination concentration (10⁶ spermatozoa mL^–1). Presumptive zygotes were cultured in SOF medium supplemented with FCS (2.5%) and BSA (5 mg mL^–1) in an incubator (38.3°C, 5% CO₂, and maximum humidity). Embryo development was evaluated in terms of cleavage (Day 3), blastocyst (Day 7), and hatching rates (Day 10). Mean rates were analysed by chi-squared test and ANOVA, and significance was considered when P < 0.05. The results obtained from the different groups are shown in Table 1. Cleavage, blastocyst, and hatching rates were not different among groups. We conclude that, under our experimental conditions, even minimal concentrations of eCG (0.015 IU) may be a viable and effective alternative in the replacement of FSH for the IVM of bovine oocytes.

Table 1.  Cleavage, blastocyst, and hatching rates of the experimental groups (1, 2, 3, 4, and 5) and control group¹

Fellowships and support by CAPES and FAPESP.