Accuracy of trans-abdominal ultrasound pregnancy diagnosis in sows using a linear or sector probe

The assessment of an early and reliable pregnancy diagnosis in sows is very important for limiting the number of non-productive days in sow herds. The aim of the present study was to investigate the accuracy of trans-abdominal ultrasound detection for early pregnancy diagnosis in sows under field conditions. Particular attention was paid to the time when a reliable diagnosis can be made, and to possible differences between two commonly used types of scanners. In total, 202 sows from two herds were tested daily with scanners A (linear transducer of 5 MHz) and B (sector transducer of 3.5 MHz) from day 16 until 25 after insemination. Ninety-three percentage of the sows were pregnant 36 days after insemination. Using ultrasound, the first pregnancy could be detected already 18 days after insemination. The sensitivity, specificity and overall accuracy were higher than 95% from day 24 (scanner A) or day 23 (scanner B) post-insemination onwards. The positive predictive values from day 19 onwards were consistently higher than 95% with both types of scanners, whereas the negative predictive values were consistently low for both scanners during the entire period. The sensitivity of testing tended to be slightly lower in sows with a litter size of <10 total born piglets, compared to sows with 10 or more piglets. In conclusion, pregnancy diagnosis in sows using trans-abdominal ultrasound testing can be assessed quickly and reliably under field conditions from day 23 of gestation onwards. Predictive values of positive test results were high in these herds, whereas those of negative test results were low. This implies that sows with a negative test result early in pregnancy should be retested later.