Transabdominal ultrasound for detection of pregnancy, fetal and placental landmarks, and fetal age before Day 45 of gestation in the sheep

Detection of pregnancy during early gestation is advantageous for flock breeding management. Transabdominal ultrasound is a practical and efficient approach for monitoring pregnancy and fetal growth in small ruminants. However, there is limited information using the transabdominal technique before Day 45 of gestation in sheep. Therefore, our objective was to determine how accurately transabdominal ultrasound could be used to detect pregnancy, to identify pregnancy landmarks, and to quantify fetal length before Day 45 in ewes. Multiparous Western White-faced ewes (n = 99) were estrus synchronized and exposed to one of four Dorset rams. The day a ewe was marked by a ram was considered Day 0 of gestation. Ewes not remarked by Day 20 were separated for ultrasonography. To detect pregnancy and landmarks, ewes were scanned three times per week between Day 26.0 ± 0.3 (mean ± standard error) and Day 40.0 ± 0.2. A single technician performed all scans in the right nonhaired abdominal pit using a real-time portable Eazi-Scan machine and a 5-MHz linear rectal transducer. All data were analyzed using the MIXED procedure in SAS (with repeated measures where appropriate). Because of rebreeding activity, 113 ultrasound periods were initiated. The specificity and positive predictive value were 100% during the entire study. The accuracy, sensitivity, and negative predictive value of ultrasound scanning were greater than 90% beginning at Day 33 ± 1. On average, pregnancy (n = 85) was detected at Day 28.7 ± 0.4 and nonpregnancy (n = 28) at Day 25.5 ± 0.6. Three early fetal losses were identified at Day 39.7 ± 0.7. In pregnant ewes (n = 82), the overall accuracy of fetal counting was 78%. The first observance of an enlarged uterus (P = 0.05) and pregnancy (P = 0.03) was detected earlier when multiple fetuses were developing compared with singletons. Placentome evagination was first observed earlier in triplets compared with twins and singletons (P = 0.02). Fetal length increased with day of gestation (P < 0.0001) but not fetal number (P = 0.72). A fetal number by day of gestation interaction (P = 0.01) indicated differences in fetal length at Day 29 ± 1 and Day 32 ± 1. These data demonstrate that a portable ultrasound using the transabdominal technique can be used to accurately determine pregnancy, identify landmarks indicative of gestation, and estimate fetal age, before Day 45 of gestation in sheep.