Diagnosing pregnancy is a valuable management tool used by small ruminant producers to allow for better nutritional management, rebreeding management, and/or culling decisions of subfertile and infertile females. Identifying ewes carrying multiple fetuses is also useful to producers so that these animals can be fed appropriately to avoid pregnancy toxemia.
Transabdominal Ultrasonography of Ewes
Courtesy of Dr. Clare Scully.
Courtesy of Dr. Clare Scully.
Transabdominal ultrasonography is the most common tool used to diagnose pregnancy in small ruminants. Several distinct ultrasonographic techniques are used:
A-mode: The transducer emits ultrasonographic waves that penetrate abdominal structures and are reflected when they meet high acoustic impedance interfaces (eg, fluid). A-mode ultrasonography is a quick, convenient, and simple technique; however, it cannot predict fetal number or viability.
Doppler: Doppler devices use the Doppler shift principle to detect fetal heartbeats and blood flow in uterine and fetal vessels.
B-mode: This method provides visible, real-time imaging of the uterus. B-mode ultrasonography is an accurate, rapid, safe, and practical means for diagnosing pregnancy, determining fetal number, and estimating gestational age.
Accuracy for pregnancy diagnosis using transabdominal ultrasonography is > 80% after 31 days of gestation. What ultrasonography shows depends on the number of days of gestation:
< 35 days of gestation: hyperechoic fetus in fluid-filled (anechoic) uterine horn
> 35 days of gestation: fetus in fluid-filled uterine horn and “C”-shaped or doughnut-shaped placentomes detectable (see )
45–50 days of gestation: C-shaped or doughnut-shaped placentomes are very obvious; best time for fetal number determination
After 50 days of gestation: C-shaped or doughnut-shaped placentomes are very obvious but because of the size of the fetus(es), determining fetal number is not possible (see ).
For More Information
Bayne JE, van Santen E, Cole RC. Ultrasonographic analyses of fetal gastrointestinal characteristics and correlations with gestational age and maturity in sheep. Small Rumin Res. 2025;246:107485.
Roberts, Jennifer. Pregnancy diagnosis in small ruminants. In: American Association of Bovine Practitioners 55th Annual Conference Proceedings. 2023.
