Fetal and placental traits at day 35 of pregnancy in relation to the estrogen receptor genotype in pigs

Fetuses from gilts with estrogen receptor (ESR) genotype AA (AA-AA and AA-A B) and BE (BB-AB and BB-BB) were compared at Day 35/36 of pregnancy, to exa mine whether fetal ESR genotype nested within maternal ESR genotype would a ffect fetal traits. Furthermore the relation of fetal body weight and fetal heart weight to various placental traits were evaluated relative to ESR ge notype. Fetal and placental weight and length, and implantation surface are a were not affected by fetal ESR genotype nested within maternal ESR genoty pe. Fetal weight was related similarly to placental length, placental weigh t, and implantation surface area: up to a certain threshold value (40 cm, 4 0 g and 250 cm(2), respectively), an increase in the trait was associated w ith an increase of fetal weight. Thereafter, fetal weight did not change an ymore. Thus, at Day 35/36 of pregnancy porcine fetuses seem to have a maxim um growth potential. The percentage of AA-AA fetuses that had not reached t his maximum growth potential was larger than of the other three genotype co mbinations studied, and therefore a higher subsequent fetal mortality may b e expected in this group. Hearts of AA-AB fetuses were significantly heavie r than those of BB-AB and BB-BB fetuses and tended to be heavier than those of AA-AA fetuses. The reason for this hypertrophy is unclear, but might be related to a difference in placental vascularity. Heart weight of fetuses from BE gilts increased with fetal weight, while heart weights of fetuses f rom AA gilts did not. Heart weight increased with an increase of placental length and implantation surface area up to 51 cm and 437 cm(2), respectivel y, and thereafter decreased again. For BB-AB fetuses a similar relation was found between heart weight and placental weight, while heart weight of the other three genotype combinations remained unaffected as placental weight increased. The fetus and placenta are continuously changing during early pr egnancy, therefore different mechanisms may change the demands for cardiac output. However, keeping in mind that placental size and blood volume are r elatively large, placental vascularity and vascular development may play a major role. Therefore, further research on heart size, placental size and v ascularity, relative to ESR genotype, is recommended. (C) 2000 by Elsevier Science Inc.