On the Livestock Herd Health and Reproduction Service, we performed pregnancy checks on multiple herds of ewes who had been bred by artificial insemination. The ultrasound was a great way to quickly and accurately diagnose which sheep were pregnant.
Ruminats have a syndesmochorial cotyledonary placenta. This describes the attachment of fetal membranes and blood supply to that of the mother’s. Unlike people and other primates, the ruminant maternal-fetal placental relationship is less invasive. The maternal and fetal membranes join at multiple circular unions instead of becoming diffusely united across the entire placenta.
The maternal-fetal placental unions in ruminants are called placentomes. A placentome is made up of the maternal caruncle and the fetal cotyledon. Cows have a convex placentome, whereas sheep and goats have a concave placentome. For this reason, they look differently on ultrasound examination. Sheep and goat placentomes look like donuts consisting of a bright white outer ring and a dark black center. Cows, in contrast, have a uniformly circular white placentome.
To locate the uterus and any fetuses or other signs of pregnancy, it is important to find the bladder as a landmark within the abdomen. It is a distinctive circular, black structure. Once the bladder is located, the uterus can be found immediately cranial to it (i.e., toward the head). When evaluating the uterus, it is important to look for placentomes or fetuses.
Ultrasound is a reliable and easy-to-use tool to quickly confirm the presence of a fetus and is a great resource for herd pregnancy checks, especially in small ruminants.