To perform fetal gender determination in the mare by ultrasound during early and advanced gestation

Abstract

Summary: This study aims to review current knowledge on equine fetal sexing with special reference to the authors field experience using the non-invasive transabdominal approach. Early gender determination performed transrectally by identifying the genital tubercle is specific with a small time frame; it is best performed from day 59 until 68. The examiner has to be experienced to scan the right planes for finding the genital tubercle in either sex. Advanced sex determination can be performed transrectally from 90 up to 140 days of gestation, afterwards reaching the fetus hindquarters transrectally is almost impossible and the transabdominal alternative has to be chosen. External genitalia and gonads have to be found and good knowledge of fetal anatomy is required. For more advanced gestation, the importance of representing the gonads and especially outlining their B-Mode echotexture and vascularisation by Doppler sonography increases. For the transrectal approach for gender determination, mares have to be calm and relaxed, so the use of sedation and smooth muscle relaxants might be necessary and the risk of perforating the rectum has to be taken into consideration. Transabdominal examination shows high acceptance in mares and bears a low risk, sedation is not necessary and movement of mare and fetus can be compensated easily by moving the ultrasound probe along the abdomen. Equine fetal sex determination is a tool in equine reproductive medicine which becomes more important and interesting for breeders in order to plan the mare s future breeding prospects. With enough time, patience, practice and good equipment it can be performed by practitioners easily as an additional service for clients. The method to be selected depends on the stage of gestation and on fetal presentation. If movements of the fetus prevent the accomplishment of sex determination, the examination should be repeated later. Advantages of gender determination during advanced gestation by transabdominal ultrasound other than economical reasons are the accomplishment of a check up on pregnancy and fetal well-being, great acceptance by the clients and a good way to perform gestation control in ponies and small horses, although this may take more time for preparation and examination.Keywords: mare / fetal gender determination / transrectal ultrasonography / transabdominal sonography / reproduction Citation: Tönissen A., Martinsson G., Otzen H., Schürmann K., Schütze S., Ertmer F., Kassens A., Sielhorst J., Brehm R., Sieme H. (2015) To perform fetal gender determination in the mare by ultrasound during early and advanced gestation. Pferdeheilkunde 31,[153][154][155][156][157][158]

Transabdominal ultrasonographic determination of fetal gender in the horse during mid-gestation – a comparative study using randomized video images to investigate variation in diagnostic performance among raters, and the effect of month of gestation

“…Combined with a convex probe working at frequencies from 2 to 6 MHz. B-Mode and colour Doppler sonography were performed at 5 MHz with a scanning depth of 16 cm (as described by Tönissen et al 2015). Once the gonads were seen examination was videotaped first in BMode, than with Doppler function.…”

Equine Embryo Sexing and Ultrasonographic Foetal Sexing – Interests and Applicability

“…Although some authors mention rectal tearing as a possible risk (McGladdery, ; Curran and Ginther, ), it did not occur in any of the mentioned studies. Other authors highlight the fact that mid‐to‐late transabdominal sexing has a much wider time window span, is accessible to small stature mares, such as miniature horses and ponies (Renaudin et al., ; Renaudin, ), presents high acceptance in mares and a lower risk (Tonissen et al., ) and usually is performed in a more convenient time of the year, usually winter, when the practitioner's schedule is less charged (Bucca, ).…”

Geschlechtsbestimmung bei Pferdefeten mittels zwei- und dreidimensionaler Sonografie in der Frühgravidität

“…Graviditätstag können mittels B-Mode und Doppler-Sonografie, zusätzlich zu den äußeren Geschlechtsteilen, die Struktur und Lage der fetalen Gonaden beurteilt werden. Während die Gonaden weiblicher Feten eine Mark-und Rindenzone (B-Mode) und ein rundes Durchblutungssignal (Doppler-Sonografie) aufweisen, sind die Gonaden männlicher Feten von homogener Echotextur und mittels Doppler-Sonografie lässt sich zentral ein strichförmiges Durchblutungssignal darstellen [11]. Die transrektale Darstellung der Gonaden ist bis zum 140.-180.…”

“…Die transrektale Darstellung der Gonaden ist bis zum 140.-180. Graviditätstag möglich [11] [12]. Zu einem späteren Zeitpunkt sind die fetalen Gonaden sowie die fetalen äußeren Geschlechtsteile transrektal nicht mehr erreichbar und die Geschlechtsbestimmung erfolgt über die transabdominale Ultraschalluntersuchung [13][14] [15].…”