In addition,
with 28-d pregnancy examinations, there is the potential
for incorrect diagnosis. Pieterse et al. (1990) found
that sensitivity and specificity of pregnancy diagnosis
with ultrasound when conducted between 21 and 25 d
post-AI was lower than pregnancy diagnosis conducted
between 26 and 33 d post-AI. Uncertain cases may be
(conservatively) labeled as pregnant so that the cows
in question are not subject to resynchronization. After
reexamination, these cows may not be pregnant, and
these cases show up as embryonic losses (even though
the cow may not have been pregnant at the time of the
initial examination). In the present study, herds that
had 28-d pregnancy examinations had a >2% higher
average conception rate than those that carried out
≥35 d pregnancy examinations.