A number of mechanical methods are available for the diagnosis of pregnancy and the determination of foetal numbers in sheep. The application of four ultrasonic systems currently used commercially was investigated.

The ‘scanning window’ in the ewe is apparent between approximately 45 to 100 days of pregnancy. Highly accurate pregnancy diagnosis and prediction of foetal numbers have been reported using the real time scanning technique. However, considerable variation in expertise can exist between operators while further discrepancies emanate from the different methods used to calculate predicted success rates. The estimation of operator accuracy from trial work is complex since errors may arise from both over- and under-estimation of foetal numbers resulting in confusion when pregnant ewes are subsequently grouped incorrectly. A true estimate of operator accuracy should reflect relative foetal numbers predicted.