Abstract
Morphological changes in the placenta at periparturition and the involvement of apoptosis controlling cell populations in the placentome were evaluated in Holstein and Nelore cows. Twenty-two Holstein cows at the end of gestation with normal non-induced parturition (group I) and 10 Holstein cows with induced parturition (group II) were used in this study. In addition, groups III and IV were constituted by 10 Nelore cows at the end of gestation with normal non-induced parturition and 21 Nelore cows with induced parturition, respectivelly. Binucleate trophoblastic cells, epithelial caruncular cells and apoptotic bodies were quantified by light microscopy. Apoptosis was further evaluated by transmission electron microscopy, ELISA and DNA electrophoresis in agarose gel. The number of caruncular epithelial cells did not vary between breeds with normal or induced parturition. The number of binucleate cells was significantly different between Holstein and Nelore cows with normal non-induced parturition (groups I vs. III), but their numbers were not significantly different between breeds when parturition was induced. In cows with normal non-induced parturition, the intensity of apoptosis, as assessed by morphometric analysis and ELISA, was significantly higher in group I when compared to group III. However, no difference in the intensity of apoptosis was found between groups II and IV. Characteristic apoptotic ladder pattern of DNA fragmentation was detected by agarose gel electrophoresis. Ultra-structural features of apoptosis in maternal and fetal epithelium as well as capillary vascular endothelium were identified by transmission electron microscopy. In conclusion, in Nelore placental maturation occurs precociously when compared to Holstein. In both breeds, apoptosis is an active physiological event that seems to be required for maturation and normal post-partum release of the placenta.
Highlights
Reproductive efficiency is a crucial factor for the success of the cattle industry, being directly related to the prompt recovery of the reproductive tract during the post-parturition period
It was empirically observed that the time from fetal expulsion to placental release is shorter in Nelore cows than in Holstein cows, and that the hystologic reorganization in the placentome seems to be precocious in zebu compared to Holstein cows, reinforcing the need to evaluate possible morphological differences between the placentomes of these two breeds
Holstein cows from gestation with normal non-induced parturition (group I) had in average 4h and 23min from fetal expulsion until complete release of the placenta
Summary
Reproductive efficiency is a crucial factor for the success of the cattle industry, being directly related to the prompt recovery of the reproductive tract during the post-parturition period. Several changes in the cell population of the placentome take place throughout the gestation. Such changes are required for placental maturation and release of the fetal portion of the placenta after parturition. Placental maturation includes corium degeneration, maternal connective and epithelial tissues alterations (Wooding, 1983; Barreto Filho, 1992; Wango et al, 1992), and specially a significant decrease in caruncular epithelial cells and binucleate epithelial cells of the trophoblast (Gross et al, 1991; Williams et al, 1987; Santos, 1995). It has been empirically observed that the occurrence of placental retention in zebu cows is lower when compared to European breeds. The length of gestation is shorter in zebu cattle as compared to European breeds (Barreto Filho, Marques Júnior, 1993)
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