Abstract

High merit mares obtain their utmost productive value at the same time their reproductive soundness diminishes. The aim of our study was to compare the developmental competence of equine oocytes from young and old mares after intracytoplasmic sperm injection (ICSI) and in vitro culture. Ovaries from young and old mares were obtained from a pool of slaughterhouse animals that have been previously selected by overall good body condition, reproductive status, and age. Young mares were 3 to 8 years old, and old mares were more than 15 years old. The age of all mares was determined by teeth observation and reproductive status by ultrasonography. Oocytes were obtained from ovaries 1 h postmortem by individual dissection of follicles between 10 and 25 mm and scraping of the follicle wall with a bone curette. Recovered oocytes were matured in vitro for 24–30 h, and all oocytes with an intact cytoplasm and a visible polar body were subject to ICSI and cultured for 7.5 days in SOFm. The maturation rate, cleavage, and embryo development rate and mean number of blastomeres at 7.5 days of culture were compared between oocytes and embryos from young and old mares. Maturation, cleavage, and developmental rates were analyzed by Chi Square and Fisher exact test, whereas the mean number of blastomeres at 7.5 days of culture was compared by one way ANOVA and t-test. A total number of 54 oocytes from young mares and 37 oocytes from old mares were obtained. There were no significant differences between the maturation, cleavage, or embryo development rates between young (79.63, 56.41, and 18.18%) and old (91.89, 63.33, and 15.79%) mares. In addition, the mean number of cells on embryos from each group did not differ significantly (57.75 v. 81; young v. old). Our preliminary results show that similar in vitro rates are achieved when oocytes from young or old mares are matured and fertilized in vitro by ICSI. This does not correlate with the reproductive senescence in old mares and the result obtained with other reproductive techniques. Further studies will determine if pregnancies are equally achieved using in vitro produced embryos from both age groups.