Discussion
The results of the present study show that the changes of
uterine blood flow in response to oxytocin challenge can be evaluated
using Doppler sonography in puerperal dairy cows. Oxytocin
challenge decreased uterine blood supply on day 2 pp but not on
day 5 pp in healthy cows, suggesting that the uterine responsiveness
to oxytocin decreases with time postpartum. Furthermore,
oxytocin injection did not alter uterine blood flow on day 2 pp in
cows with RFM, suggesting that the uterus of cows with RFM is
not capable of responding to oxytocin stimulus early postpartum.
Uterine BFV and PI were measured in both uterine arteries,
UA-ipsi and UA-cont, by using transrectal Doppler sonography.
The uterine artery represents the main blood supply of the uterus,
and therefore, uterine blood perfusion can be determined by investigating
both the uterine arteries (Bollwein et al., 2000). On day 2
pp, BFV decreased rapidly and vascular resistance increased
5 min after oxytocin administration; but not after saline.