How accurate is foetal aging at pregnancy scanning to predict lambing date?

Abstract

Transabdominal ultrasound scanning to determine pregnancy status and litter size is common practice to assist in management of ewes. Accurate litter size data can also be used as data for genetic evaluation, substituting for data collection at birth (Bunter et al. 2016). At small additional cost, foetal age can also be estimated at pregnancy scanning. Accurate determination of foetal age at scanning would enable optimum management of ewes based on both litter size and expected date of lambing. In addition, foetal age could enable age adjustments when lambing date is unknown, improving accuracy of genetic evaluation for young animals.