Effects of a protracted induction of parturition on the incidence of retained placenta and assessment of uterine artery blood flow as a measure of placental maturation in cattle.

The objectives of the present study were to compare the effects of a protracted and a conventional induction of parturition on the incidence of retained placenta, and to evaluate the suitability of transrectal Doppler sonography of the uterine arteries as a noninvasive method for the assessment of placental maturation. Protracted induction of labor (PIP) was precipitated in 13 cows by the administration of 1.3 mg dexamethasone im twice daily between Days 268 and 273 of gestation, and 40 mg dexamethasone im on Day 274 of gestation. For conventional induction of labor (SIP), 10 cows received 40 mg dexamethasone on Day 274 of gestation. A third group was not treated and served as control (SPON; N = 11). Blood flow volume (BFV) and resistance index in the uterine arteries were measured with Doppler sonography once a day from Day 268 of gestation until labor. After each ultrasonographic examination, blood samples for determination of steroid hormones were taken. Incidence of retained placenta was lower (P < 0.05) in group SPON (9%) compared with groups PIP (54%) and SIP (70%). In the last 7 days before parturition uterine BFV and resistance index did not change (P > 0.05) and did not differ between groups SPON, PIP, and SIP (P > 0.05). Resistance index was higher (P < 0.001) in cows with retained placenta compared with cows with released placenta, and BFV did not differ (P > 0.05) between them. Total estrogen concentrations increased by 283% (P < 0.001) in group PIP and by 60% (P < 0.05) in group SPON between Days -7 and -1 before parturition. They stayed constant (P > 0.05) until Day -2 in group SIP, but increased (P < 0.05) after the high dosage of dexamethasone within 1 day by 140%. Total estrogen levels were higher (P < 0.05) in cows with released placenta than in cows with retained placenta. In conclusion, a protracted compared with a short induction of labor results in higher estrogen levels before term, but does not affect incidence of placental retention. Neither alterations in placental maturation nor changes in steroid hormones influenced uterine blood supply. Therefore, Doppler sonography of uterine arteries is unsuitable to investigate the process of placental maturation induced by glucocorticoids in cows. Nevertheless, disturbances in the placental maturation process in cows with retained fetal membranes after parturition can be detected before parturition by a higher uterine blood flow resistance in the uterine arteries.