298 Effects of parity on late gestational uterine blood flow and hemodynamics in beef cattle

Abstract

Abstract To determine parity effects on late gestational uteroplacental blood flow, uterine artery hemodynamics were measured in 13 primiparous and 11 multiparous (parity 3 and 4) non-lactating, fall-calving crossbred females beginning 109 d prepartum. Females were nutritionally managed as one group to meet or exceed nutrient requirements. Transrectal color Doppler ultrasonography of the both uterine arteries was conducted 3 to 6 times per female across late gestation, ending at approximately 20 d prepartum. Data were analyzed with parity (primiparous vs. multiparous), day prior to calving, and their interaction in the model; day was a repeated effect. Dam BW was greater (P < 0.001) for multiparous than primiparous females, and increased (P = 0.004) as gestation progressed. Calf birth weight was unaffected (P = 0.87) by parity. The parity x day interaction tended to affect (P = 0.06) ipsilateral uterine artery blood flow (L/min), where multiparous cows had a greater increase per day. Total and contralateral uterine artery blood flow were unaffected (P ≥ 0.11) by parity, but increased (P < 0.001) with day of gestation. When expressed relative to dam BW, total and contralateral blood flow were greater (P ≤ 0.04) in primiparous than multiparous females; ipsilateral blood flow was unaffected (P ≥ 0.13) by parity, however. Ipsilateral pulsatility index and both resistance indices were unaffected (P ≥ 0.28) by parity and day, but day tended to affect (P = 0.07) contralateral pulsatility index. Parity did not affect (P ≥ 0.11) cross-sectional area, mean velocity, peak systolic velocity, and end diastolic velocity of either uterine artery, but all increased (P < 0.001) as gestation progressed. Heart rate was greater (P = 0.03) in primiparous than multiparous females. Data suggest that uterine artery blood flow and heart rate may be altered in primiparous females, even when birth weight is unaffected by parity.