Protracted induction of parturition enhances placental maturation, but does not influence incidence of placental retention in cows

摘要

As the etiopathology of retained placenta is still not resolved in cattle, we compared the effects of protracted induction of parturition (PIP) and conventional induction of parturition (SIP) on placental maturation and the occurrence of retained placenta. PIP was induced in 13 cows by 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 SIP, 10 cows received a single injection of 40 mg dexamethasone on Day 274 of gestation. A third group (SPUN, n = 11) served as a nontreated control group. Within 2 hours after birth, two placentomes were extracted from the uterus and used for assessment of placental maturation by histology and immunohistochemistry. Incidence of retained placenta was lower (P < 0.05) in group SPUN (9%) compared with groups PIP (54%) and SIP (70%). Staining with Masson's trichrome and pan-cytokeratin indicated a higher degree of atrophy and flatness of the maternal crypt epithelium in cows with physiological release of fetal membranes (REL) compared with cows with retained placentae (RET). Staining with anti-caspase-3 ratified the observations as more apoptotic cells were detected in groups SPUN and PIP compared with group SIP; however, data were not statistically significant. Additionally, the expressions of the potent vasodilators endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) were evaluated. Both eNOS and iNOS were only expressed in chorionic tissue. Endothelin-1 (ET-1), a major vasoconstrictor, showed positive staining in maternal crypt epithelium and in chorionic epithelium. No differences were found for iNOS and eNOS and ET-1, neither among the experimental groups nor between RET and REL cows. These findings indicate that a PIP results in increased placental maturation, but does not influence the incidence of placental retention in cows. The expression of vasoactive substances does not seem to be related to the placental separation process.