134 Effects of Gas Tension During Culture upon Development of Bovine Embryos from Beef (Nellore) and Dairy (Girolando) Breeds
Authors: Grázia J. G. V. , Lacerda L. G. , Siqueira L. G. B. , Pellegrino C. A. G. , Grapiuna L. S. , Sollecito N. V. , Viana J. H. M. 
Published: November 2018

Culture of bovine embryos is a critical step during in vitro embryo production (IVEP) and, as such, has been the focus of numerous studies on cattle IVEP. Improvements of culture conditions to mimic the in vivo maternal microenvironment involves studying the optimal gas tension for pre-implantation embryonic development. In the commercial conditions, there is great variability in results, in part because of the difference between breeds and donors. The objective of this study was to evaluate the effects of culture in high or low oxygen tension upon the development of embryos from a crossbred dairy breed (Girolando F1; Gir × Holstein) and a beef Bos indicus breed, Nellore. We collected data from an IVEP commercial operation located in a tropical area of southeastern Brazil (Minas Gerais State) from February to May 2017. The study was designed in a 2 × 2 factorial arrangement of treatments: 2 O2 tensions during culture (5%, low O2 v. 20%, high O2) and 2 breeds (Nellore, beef v. Girolando F1, dairy). Thus, the following 4 groups were studied: Nellore-high O2 (n = 86 donors), Nellore-low O2 (n = 107 donors), Girolando F1-high O2 (n = 114 donors), and Girolando F1-low O2 (n = 110 donors). Outcome variables were the number of cleaved embryos 72 h post-insemination (hpi), cleavage rate relative to the total number cumulus–oocyte complexes (COC) put in culture, number and percentage of blastocysts 192 hpi relative to the structures kept in culture. Variables that were not normally distributed were transformed using the formula log(y + 0.05). Data were analysed using the GLM procedure of SAS (SAS Institute Inc., Cary, NC, USA) for the main effects of gas tension (low v. high O2) and breed (Girolando F1 v. Nelore). Results are shown as mean ± SEM. Gas tension affected the number of cleaved embryos (10.52 ± 0.92 v. 8.33 ± 0.72 for high and low O2, respectively; P < 0.01) and cleavage rates (40.58 ± 2.49 v. 44.41 ± 2.88 for high and low O2; P < 0.01 in Nellore), but did not affect these variables in Girolando F1 donors (13.23 ± 1.33 v. 10.76 ± 0.76 cleaved embryos, for high and low O2; P = 0.63; 58.01 ± 2.00 v. 60.19 ± 1.97 cleavage rate, for high and low O2; P = 0.80). Nonetheless, the number and percentage of blastocysts were not affected by gas tension in either breed. Results for Nellore were 4.99 ± 0.56 v. 3.51 ± 0.38 blastocysts in high and low O2, respectively (P = 0.051) and 41.92 ± 3.91% v. 39.81 ± 3.77% blastocysts, in high and low O2 (P = 0.11). For Girolando F1, numbers of blastocysts were 5.84 ± 0.66 v. 4.24 ± 0.39 in high and low O2 (P = 0.19) and percentage of blastocysts 49.14 ± 2.97% v. 49.11 ± 3.40% in high and low O2 (P = 0.46). These results suggest that oxygen tension during culture affects IVEP differently depending on breed. The initial period of culture, recognised as critical in IVEP, seemed more sensitive to high O2 tension, particularly in Nellore.