A comparison of a mechanical sector and a linear array transducer for ultrasound-guided transvaginal oocyte retrieval (OPU) in the cow

A comparison was made between a linear array and a mechanical multiple angle sector (MAP) transducer for ultrasound-guided transvaginal oocyte retrieval (ovum pick-up, OPU) in the cow. The ovaries of five dairy cows were punctured, in a twice-weekly OPU program lasting for 4 weeks, using two different 5.0-MHz transducers equipped with an identical disposable needle-guidance system. Both ovaries were visualized using each transducer before puncture and the number of follicles with a diameter of less than 5 mm (small) and with a diameter equal to or greater than 5 mm (large) was recorded. Subsequently, one ovary of the pair was punctured guided by the MAP, while the other was punctured using the linear array transducer. During the next puncture session on a given animal, the two systems were switched and used on the alternate ovary in a crossover design. Parameters assessed for each system were: the total number of follicles visualized in each diameter class, and the total number of retrieved oocytes per cow. A significant difference was found for the ability to visualize smaller follicles in favor of the MAP transducer, with an average visualization of 71.6 +/- 30.3 small follicles per cow during the 4-week trial period, compared to 59.8 +/- 25.7 for the linear array transducer (t-test for paired samples, P = 0.007). No differences were found in the visualization of large follicles. A numerically greater number of oocytes were retrieved using the MAP transducer, compared to the linear array, (averages of 14.2 +/- 7.2 versus 7.4 +/- 6.1, respectively), although these differences were not statistically significant. In conclusion, both systems can be effectively used for oocyte retrieval in the cow, however, the MAP transducer demonstrated superior visualization of small follicles.