Early pregnancy diagnosis by transrectal ultrasonography in ewes

Two studies were performed to evaluate early pregnancy diagnosis by transrectal ultrasonography (TRUS), using a 7.5-MHz transducer in ewes. In the first study, the objectives were to determine the earliest date that a reliable pregnancy diagnosis could be made (percentage of ewes detected pregnant between days 15 and 20 after mating). In the second study, the objective was to confirm the findings of the first study using a randomized controlled trial. In both studies, the ewes were restrained in dorsal recumbency, using a special chute that maintained the pelvis at an angle of 30–35◦ lower than the head. In the first study, 30 Suffolk ewes were synchronized and maintained with 2 rams for 5 days. Each ewe was subjected to the first TRUS on day 15 after mating and daily thereafter until day 20 (estrus = day 0). Pregnancy was defined as the presence of an embryo or extra-embryonic membranes. The percentage of ewes detected pregnant at days 15, 16, 17, 18, 19 and 20 were 0% (0/30), 26.7% (8/30), 86% (24/30), 90% (27/30), 96.7% (29/30) and 100% (30/30), respectively (P < 0.001). In the second study, 390 TRUS examinations (TRUS-1) were performed on ewes from 10 to 50 days after mating in a breeding program (group mating, hand mating, cervical and intrauterine AI; breeding group; n = 270) or with vasectomized rams (vasectomized group; n = 120). The breeding date and the status of breeding were unknown to the operator. Thirty of these ewes were mated with vasectomized rams and used repetitively four times as the non-pregnant control group. All females had a subsequent TRUS (TRUS-2) between 7 and 30 days after the TRUS-1 examination. The second TRUS was used as the standard test against which the performance of the TRUS-1 was compared. The percentage of ewes correctly diagnosed at day 15 or less, days 16, 17, 18, and 19 in the breeding group were 0% (0/29), 31.3% (5/16), 40% (8/20), 70% (7/10), and 100% (14/14), respectively (P < 0.001). All the diagnoses of ewes more than 20 days following mating in the breeding group, were correctly predicted (n = 181), as well as all ewes from the vasectomized group (n = 120). It could thus be concluded that the earliest pregnancy diagnosis using a 7.5-MHz transducer by transrectal route based on the presence of positive signs of pregnancy is at day 16 and the maximum sensitivity and negative predictive value was reached at day 20 following breeding. © 2008 Elsevier B.V. All rights reserved.