IN-VITRO DEVELOPMENT OF DAY-2 EMBRYOS OBTAINED FROM YOUNG, FERTILE MARES AND AGED, SUBFERTILE MARES

This study was designed to investigate the development of day 2 embryo s obtained from young and aged mares, co-cultured with oviductal epith elial cells obtained from mares in each age group in a 2 x 2 crossover design. Young, fertile mares (n = 19; 2-7 years of age) and aged, sub fertile, mares (n = 16; 17-24 years of age) were used as embryo and ov iductal epithelial cell donors. Embryos (n = 37) were collected from t he oviducts 2 days after ovulation and were paired (embryos obtained f rom young mares with embryos obtained from aged mares) so that eight p airs were co-cultured with young mare oviductal epithelial cells and e ight pairs were co-cultured with aged mare oviductal epithelial cells. Five additional embryos obtained from young mares were co-cultured wi th oviductal epithelial cells from either young mares or aged mares bu t were not paired. Embryos were co-cultured for 7 days at 38.5 degrees C in 5% CO2 or until morphological degeneration was detected. The pro portions of paired embryos that reached the blastocyst stage were simi lar for embryos obtained from young mares and embryos obtained from ag ed mares after co-culture with oviductal epithelial cells from young m ares (6 of 8 versus 5 of 8) or from aged mares (6 of 8 versus 5 of 8), respectively. Although the overall rate of development of embryos to blastocyst from both young mares and aged mares was similar, blastocys ts developing from embryos obtained from aged mares were inferior to b lastocysts obtained from young mares in terms of number of cell nuclei , quality score, and diameter at day 7. The results of this experiment indicate that the high rate of early embryonic loss in aged, subferti le mares may be due to inherent developmental defects in their embryos , but does not appear related to the ability of embryos from aged, sub fertile mares to reach the blastocyst stage.