A comparison of pregnancy diagnosis methods in commercial sheep using lambing as a gold standard

Abstract

Several methods are used for pregnancy diagnosis in sheep, including ultrasonography and
detection of pregnancy associated glycoproteins (PAG) in blood, using either an IDEXX Rapid Visual
Pregnancy Test (RVPT) kit or IDEXX Bovine Pregnancy Test (BPT). The objective was to compare
transabdominal ultrasonography, RVPT and BPT for pregnancy diagnosis in sheep, with lambing results
as a gold standard. Crossbred ewes (n = 196) from 3 commercial flocks were exposed to a ram for a 60-
day breeding period. Transabdominal ultrasonography was performed 30 days after ram removal and a
blood sample was concurrently collected. Results of transabdominal ultrasonography, RVPT, and BPT
were compared to lambing results. For ultrasonography, RVPT and BPT, sensitivities were 98.6, 97.2,
and 95.1%, respectively (95% CI were 95 - 99.8, 93 - 99.2 and 90.1 - 98,) and specificities were 100, 94.3
and 98.1% (95% CI were 93.2 - 100, 84.3 - 98.8 and 89.9 - 99.9). Seven pregnant ewes were misclassified
as not pregnant on the BPT, whereas 4 of these ewes were also misclassified as not pregnant on the
RVPT. We concluded that RVPT, BPT, and transabdominal ultrasonography had similar sensitivity and
specificity when compared to lambing results.