The objective of this study was to examine whether an oxytocin challenge test (OCT), evaluated by mea-
suring the changes in uterine blood flow using transrectal colour Doppler ultrasonography, is a suitable
non-invasive method to determine uterine contractility in puerperal dairy cows. The changes in uterine
blood flow during uterine contractions induced by oxytocin were evaluated on days 2 and 5 postpartum
(pp). Twelve clinically healthy Holstein cows were randomly assigned into two groups: (1) oxytocin
group (n = 7), 50 IU oxytocin injected IM and (2) control group (n = 5), 5 mL saline injected IM. Blood flow
volume (BFV) and pulsatility index (PI) in the uterine arteries were determined before and after injection
for 120 min on days 2 and 5 pp.
BFV declined and PI increased rapidly after oxytocin injection on day 2 (P < 0.05), whereas oxytocin on
day 5 pp did not cause changes in blood flow parameters. The result confirmed that uterine responsive-
ness to oxytocin decreases with time postpartum in healthy cows. The same OCT was applied in cows
with retained fetal membranes (n = 6) on day 2 pp, however uterine blood flow showed no change after
oxytocin injection. The results showed that an OCT on day 2 pp may be a useful method for investigating
the uterine contractile response to oxytocin (reflected as the decrease of uterine blood flow) and the
potential pathophysiology of uterine involution in cows.