[Sonographic diagnosis of pregnancy and determination of fetal number and gestational age in ewes].

The aim of the present study was to evaluate accuracy of transabdominal ultrasonography for pregnancy diagnosis, determination of fetal number and estimation of gestational age in ewes. A total of 1068 ewes from 8 different flocks (Swiss White Alpine n = 379, Swiss Black-Brown Mountain n = 189, Oxford-type n = 164, Ostfriesian n = 154, Texel n = 104, Lacaune x Osfriesian crossbred n = 78) was investigated using an Ovi-Scan™ ultrasound scanner with a 3.5 MHz 170° mechanical axial probe (BCF Technology Ltd., BelIshill, Great Britain). Scanning was performed transabdominally at the right inguinal region in ewes restrained in standing position. Sonographic findings were compared with lambing data recorded by the farmers. Included in the analysis were all ewes that, at the time of examination, were not pregnant and those that were pregnant between 26 and 110 days with a known lambing date and number of lambs born (n = 882). The sensitivity of pregnancy diagnosis was 97.8% and the specificity 97.6% (overall accuracy 97.8%, n = 853). Sensitivity and specificity for discrimination between single and multiple pregnancies was 95.8% and 90.5% (overall accuracy 93.9%, n = 752), respectively, when multiples were defined as positive. Discrimination between twins and triplets reached a sensitivity of 86.0% and a specificity of 99.5% (overall accuracy 98.0%, n = 458) when triplets were defined as positive. Considering a gestation period of 150 days, the mean deviation of the estimated to the effective day of gestation at examination was 5.6 ± 5.0 days (n = 781). The correlation between estimated and true gestational age was very high (r=0.936, P<0.0001). In conclusion, a highly accurate and efficient diagnosis of pregnancy with reliable estimation of fetal number and age is possible using an Ovi-Scan™ ultrasound scanner by an experienced examiner.