82 Evaluation of ovine in vitro embryo production using frozen–thawed semen from dominant and subordinate rams

In vitro embryo production (IVP) is an important tool for genetic improvement in small ruminants. For the success of IVP, semen quality is one of the most important aspects. The differences between ejaculates from the same animal and the social dominance is well documented in sheep. The objective of this research was to compare the effect of the frozen–thawed semen from dominant and subordinate crossbred rams on ovine IVP. Dominance-subordination relationship was determined with the competition test for food (Synnott and Fulkerson 1984 Appl. Anim. Ethol. 11, 283–289). Ovaries (n = 196) were collected from a slaughterhouse and transported (37°C) to the laboratory within 2 h in saline solution (0.9% NaCl) supplemented with penicillin G (100 IU/mL) and streptomycin sulfate (100 µg/mL). For IVP, IVF-Bioscience™ media were used for in vitro maturation (BO-IVM™), IVF (BO-IVF), and in vitro culture (BO-IVC). For the IVM, the cumulus–oocyte complexes (COCs) were selected (only grades 1 and 2) and matured for 24 h at 38.5°C in 5% CO₂ in air and 100% humidity. For IVF, frozen–thawed semen from an IVP proven ram (control) and semen from crossbred rams (Katahdin, Saint Croix, and White Dorper) from dominants (DO) and subordinates (SB) was used (pooled: 3 rams each). Matured oocytes (n = 1200) were divided into three groups (control, DO, and SB: 400 each, in four replicates) and fertilized in vitro using semen from control, DO, and SB rams. All semen samples (control, DO, and SB) were adjusted at a concentration of 2 × 10⁶ sperm/mL and placed with oocytes for 18 h in 38.5°C, 5% CO₂ in air and 100% humidity. The presumptive zygotes were denuded by pipetting and placed in IVC until Day 7 at 38.5°C, 5% CO₂, 5% O₂, and 90% N₂ at 100% humidity. Statistical analysis was carried out with the ANOVA procedure of the Jamovi software (version 1.2; The Jamovi Project) to evaluate percentages of cleaved embryos, 8-cell embryos, and blastocysts on Day 7 of culture, based on the initial number of oocytes entering IVM. Rates of cleavage, 8-cell embryos, and blastocysts on Day 7 were different (P < 0.05) for the control, DO, and SB groups, respectively: 67 ± 2.45%, 45 ± 4.76%, and 36.3 ± 3.5%; 48.8% ± 1.71%, 20 ± 2.94%, and 14 ± 1.83%; 54.3 ± 3.4%, 29 ± 1.83%, and 21.5 ± 2.65% (Table 1). Under the conditions of this research, SB had higher percentages for all variables compared to DO, and this effect could be due to the stress that DO rams are subjected to.