153 Effects of ewe age on oocyte viability and timing of early embryo cleavage
K. Fryc A , A. Nowak B , P. M. Bartlewski C and M. Murawski AA Department of Animal Nutrition and Biotechnology, and Fisheries, University of Agriculture in Krakow, Cracow, Poland
B Department of Animal Reproduction, Anatomy and Genomics, University of Agriculture in Krakow, Cracow, Poland
C Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada
Reproduction, Fertility and Development 34(2) 314-314 https://doi.org/10.1071/RDv34n2Ab153
Published: 7 December 2021
© 2022 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of the IETS
Reproductive capacity of the female declines with advancing age. Ageing is associated with a decrease in both the quantity and quality of oocytes in vivo and in vitro. Ovaries were collected after slaughter from Longwool ewes aged 8–9 years (group I: “old”; n = 16) or 1.5–3 years (group II: “young”; n = 14), and transported to the laboratory. Cumulus–oocyte complexes were collected from scarified ovaries, and IVM was performed in TCM 199 medium supplemented with Earle’s salt, 10% fetal bovine serum, and 5 µg mL−1 LH/FSH at 38°C for 24 h. After IVM, the oocytes were incubated with thawed, capacitated ram semen for 19 h at 38°C. Following IVF, presumptive zygotes were transferred to a 16-well dish containing Cult medium (Gynemed), and were cultured and monitored with time-lapse (TL) video imaging for 8 days. Digital images of developing ovine embryos were captured every 10 min by the Primo Vision TL system (Vitrolife). The following variables were recorded: time from IVF to the attainment of two-cell (t2), three-cell (t3), or four-cell (t4) stage; morula stage (tM); blastulation (tSB); and blastocyst formation (tBL). The duration of the second cell cycle (cc2) and of the complete synchronous cell division (s2) were calculated, and the incidence of developmental anomalies was noted. All single time-point observations were compared between the two subsets of ewes by Student’s t-test. Sixty-six oocytes were obtained and 48 were selected for TL observations after IVF (presumptive zygotes) in group I. Twenty-four zygotes (50.0%) underwent first cleavage division and 5 (10.4%) developed to the blastocyst stage. Sixteen embryos (33.3%) had morphological defects: fragmentation (n = 9), direct cleavage (n = 7), or asymmetrical cleavage (n = 2). In group II, 86 oocytes were collected and 64 used for TL observations. Forty-four zygotes (68.75%) underwent first cleavage division, 17 (26.6%) developed to the blastocyst stage, and seven embryos (10.9%) had different disorders (fragmentation, n = 4; asymmetrical cleavage, n = 3). Both the cleavage and blastocyst formation rates were higher (P < 0.05) for group II, but the percentage of embryos with various defects was greater (P < 0.01) for group I. The average time from IVF to the first cleavage (t2) was 29 h 20 min and 25 h 42 min in groups I and II, respectively (P = 0.02). The duration of cc2 also differed (P = 0.009) between the two subsets of embryos studied (4 h 14 min and 11 h 20 min, for groups I and II, respectively). The present analysis of the morphokinetic data revealed that (1) oocytes collected from “young” donor ewes had greater developmental potential and gave rise to the embryos with fewer aberrations in vitro compared with the oocytes obtained from “old” ewes; and (2) the interval from IVF to the first cleavage and the duration of the second cell cycle were both greater for group I than for group II oocytes. Sheep in vitro embryo production systems and TL imaging provide a useful tool for studying the influence of donor age on embryogenesis in mammalian species.
