82 In vitro embryo production outcomes in adult goats is affected by season

Abstract

In seasonal breeders, reproductive seasonality can have a substantial influence on the efficiency of assisted reproductive technologies. This study assessed seasonal effects on cleavage and blastocyst rates, as well as on quality of in vitro-produced (IVP) goat embryos over 18 months. In total, 2348 (autumn: 811, spring: 404, summer: 639, and, winter: 494) cumulus–oocyte complexes (COC) were recovered from slaughterhouse ovaries during 49 replicates (autumn: 17, spring: 7, summer: 15, and, winter: 10) and matured in TCM-199 with 10 ng mL⁻¹ epidermal growth factor and 100 µM cysteamine for 22 h at 38.8°C (5% CO₂ in air). Matured oocytes were fertilized with frozen/thawed semen in synthetic oviductal fluid (SOF) with 10% oestrus sheep serum. Sperm and oocytes were co-incubated for 16 h at 38.8°C in a humidified atmosphere of 5% CO₂ in air. Presumptive zygotes were cultured in SOF medium supplemented with bovine serum albumin (3 mg mL⁻¹) for 8 days at 38.8°C in a humidified atmosphere of 5% O₂, 5% CO₂ and 90% N₂. At Day 2, 10% fetal calf serum was added to the culture droplets. The embryos produced were fixed and stained with Hoechst to count their total number of cells, under an epifluorescence microscope. The results of cleavage and blastocyst rates, including hatching rate, from each routine of IVEP were considered as replicates. These data were tested for normality by the Shapiro-Wilk test, before being subjected to ANOVA, followed by Tukey HSD test. The odds ratio (OR) among seasons (autumn: breeding; spring: anoestrus) were calculated. Values of P < 0.05 were considered as significant, and the data reported are mean ± s.e.m. Cleavage rate was lower (P < 0.05) in spring (51 ± 7.1%) than in either autumn (72 ± 2.1%) or summer (71 ± 2.0%) while winter (66 ± 4.1%) had an intermediate value, being similar (P> 0.05) to all others. Indeed, greater possibility of cleavage was observed in autumn (OR: 2.43) and summer (OR: 2.39) compared with spring. The blastocyst rate from cleaved embryos was greater (P <0.05) in autumn (73 ± 2.7%) than in spring (55 ± 2.6%; OR: 2.18). As a result, the blastocyst formation rate from the initial number of COC entering IVM was greater (P < 0.05) in autumn (52 ± 2.5%) than in spring: 28 ± 4.7%, summer: 45 ± 2.3%, and winter: 42 ± 2.1%; indeed, the spring season resulted in the lowest rate (P < 0.05), compared with other seasons. Moreover, the OR in the blastocyst rate from initial number of COC was greater (P < 0.05) in autumn compared with all other seasons and lower in spring compared with winter (OR: 0.54) and summer (OR: 0.48). There were no differences (P> 0.05) in the embryo hatching (mean: 66 ± 2.0%) and blastocyst cell number (mean: 193 ± 2.0 cells). In conclusion, the breeding season (autumn) leads to improved oocyte developmental competence, resulting in greater cleavage and blastocyst yield, whereas embryo quality remained similar throughout the year. Further studies at the molecular level might indicate the mechanisms involved and provide clues to alleviate the negative effect of season.