Ultrasound-Guided Follicular Aspiration in Mares1

Abstract

The study was designed to develop a technique for collecting equine oocytes using ultrasonically guided follicular aspiration. Recovery rate and morphology of cumulus-oocyte-complexes (COC) should be related to follicular diameter in cyclic and acyclic mares. On the basis of results of follicular aspiration in vitro, the follicles from ovaries of 27 warmblood horses were punctured by ultrasound control via the transcervical method. A 6.5-mHz sector scanner and a specially designed carrier with a bitubular needle were used for aspiration. Inner and outer diameters of the needle were 0.9 mm and 1.1 mm. A constant vacuum pressure of 0.3 bar was applied during in vivo aspiration. After aspiration, the follicles were flushed up to four times. The COC obtained were classified into four groups: compact COC (A), expanded COC (B), COC with few layers of cumulus cells (C), and denuded COC (D). The total number of aspirated follicles was 332. A mean of 12.3 follicles were aspirated per animal. The mean number of recovered COC per mare was 3.4. Aspiration of follicles with a diameter of up to 20 mm delivered 96% of all COC recovered. The recovery rate differed significantly between Day 5 and Day 12 of the estrous cycle. Oocytes with few layers of cumulus cells were found in almost equal proportions in follicles < 10 mm in diameter and 10–20 mm in diameter. Only one third of COC from follicles smaller than 20 mm had a compact cumulus.