Ultrasonographic Monitoring of Fetal Growth and Fetal Weight Calculation in Sows during Gestation

Ultrasound examinations offer the possibility to monitor fetal growth and estimate fetal weight, but reference data for such techniques in pigs are rare. The aim of this study was therefore to identify suitable anatomical fetal structures for monitoring physiological growth dynamics by ultrasound examinations and to estimate fetal weight using appropriate mathematical models. For this purpose, 198 fetuses of 15 primiparous Landrace sows were examined by ultrasound on days 36, 50, 64, 79 and 92 of gestation in live sows and in utero after slaughter. Biparietal distance (BPD), rostro-occipital distance (ROD), corpus vitreum diameter, heart length, abdominal circumference (AC) and transverse and sagittal abdominal diameter were determined by ultrasound in utero, and the fetuses were subsequently ex uteri determined and weighed. Reference curves for the continuous increase in fetal parameters over the pregnancy were established. Weight estimation could be performed with linear models at a known stage of pregnancy using one or a combination of parameters. Cubic equations were developed to describe the relationships between body measurements and weight over the course of gestation. BPD, ROD and AC have been shown to be the most suitable parameters for fetal weight estimation, but in live sows, only the fetal head parameters could be easily and reliably determined. These techniques could initially be of interest for research into fetal growth, but future application in veterinary practice is also conceivable.