Real-time ultrasonic scanning in the diagnosis of pregnancy and the determination of fetal numbers in sheep.

Two trials were conducted on a total of 1120 ewes of four breeds to evaluate the use of real-time ultrasonic scanning as a means of diagnosing pregnancy, differentiating barren, single- and multiple-bearing ewes and determining actual fetal numbers in pregnant ewes. In trial 1 (566 ewes) the accuracy of an inexperienced operator, as judged against assessments of an experienced operator, improved from 81 to 100 per cent for the classification of ewes as carrying no, one or more than one fetus, and from 69 to 100 per cent for the determination of actual fetal numbers more than one. In trial 2 the accuracies of the same operator, judged against the lambing performance of 267 ewes, ranged from 90 to 97 per cent for both types of assessment, and for an experienced operator from 95 to 100 per cent (554 ewes). In both trials pregnancy was diagnosed with an accuracy of 100 per cent. It is concluded that real-time ultrasonic scanning of sheep between days 50 and 100 of gestation offers a safe and practicable means of diagnosing pregnancy and of determining fetal numbers. Accuracies of diagnosis of pregnancy of more than 99 per cent, of differentiation of barren, single- and multiple-bearing ewes of 98 per cent, and of determination of actual fetal numbers of 97 per cent can be achieved in practice at scanning rates of at least one ewe per minute. Some of the benefits to flock management and performance likely to result from the use of the technique are considered.