Recovery of equine oocytes by scraping of the follicular wall with different specifications of needles and morphological analysis of cumulus oophorus

In follicular aspiration, physical aspects are of high significance for the technique to succeed, such as vacuum pressure, caliber of the needle and the way the follicular wall curettage is performed. The aim of this study was to investigate the recovery rate of equine oocytes aspirated by scraping of the follicular wall, testing different calibers of disposable needles, as well as the morphological evaluation of the cumulus oophorus complexes (COCs). Mares ovaries (n=447) obtained at a local slaughterhouse were transported to the laboratory in a thermal container (20 degrees C) and had the tunica albuginea and connective tissues dissected. The aspirated follicles had 10 to 25 mm in diameter, and 30x8 (21G 1 1/4) or 40x12 (18G 1 1/2) needles were used for the aspiration, forming group A (G-A) and group B (G-B), respectively. In G-A and G-B, 480 and 548 follicles were aspirated, respectively. Under the stereomicroscope, the oocytes were evaluated according to the quality of the ooplasm and characteristics of the cumulus cells (grade I, II, III and denuded). The statistical analysis was performed using the Student's t-test, logistic regression and test of proportions, and differences were considered significant when P<0.05. There was no difference between recovery rates of groups G-A (66.5%; 330/496) and G-B (65.5%; 359/548). In the G-A group, grade II oocytes were related to higher recovery rates (46.9%; 145/330) than grade I (23.6%; 72/330), grade III (20.6%; 59/330) and denuded oocytes (8.5%; 24/330; P<0.05). However, in G-B, there was no statistical difference regarding the quality of the recovered oocytes: grade I (23.4%; 77/359), grade II (43.2%; 145/359), grade III (22.5%; 73/359) and denuded (11.1%; 32/359). The 30x8 (21G 1 1/4) needle provided a higher proportion of grades I and II oocytes than the 40x12 (18G 1 1/2) needle, with 72.4% (239/330) and 65% (233/359; P<0.05), respectively. Both calibers of needles tested in this study provide efficient oocyte recovery rates. Aspiration with 30x8 (21G 1 1/4) needles resulted in a higher proportion of morphologically good equine oocytes for use in reproductive biotechnologies.