Regulation of embryo survival in cattle

摘要

Evidence is presented that bovine somatotrophin (bST) treatment of lactat-ing dairy cows enhances both expression of oviductal insulin-like growth factor II (IGF-II) mRNA and endometrial insulin-like growth factor binding protein 3 (IGFBP-3) mRNA between day 3 and day 7 of the oestrous cycle, mRNA encoding growth hormone (GH) receptor in endometrial tissues increased between day 3 and day 7 of the oestrous cycle. The changes induced by bST treatment may contribute to stimulation of embryo developmentand increase pregnancy rates in lactating dairy cows. Additive effects of bST and rb interferon T (rblFN-tau) to inhibit phorbol ester induction of prostaglandin F_(2 alpha) secretion in immortalized bovine endometrial cells indicates that there is interplay between their signal transcluclion pathways. Non-lactating dairy cows were killed at day 17 after oestrus to evaluate the effects of pregnancy status (cyclic versus pregnant) and bST (bST versus control) treatment on endometrial gene expression. Distinctly different mRNA and protein responses were detected between cyclic and pregnant cows that were related to luteolytic-antiluleolytic drive (that is expression of progesterone receptor, oxytocin receptor, oes-tradiol receptor a and prostaglandin GHsynthase 2 (PGHS-2)). The bST-induced changes in PGHS-2 protein (+), oxytocin receptor mRNA (+) and oestrogen receptor a protein (+) may potentially affect the mechanisms associated with maintenance of pregnancy. Two experiments were conducted to evaluate whether ovarian follicular suppression induced by biodegradable deslorelin implants would reduce either early or late embryo losses. A 450 mu g deslorelin implant used to induce ovulation in a timed insemination programme decreased subsequent foilicular development and tended to reduce early embryo losses, whereas a 2.1 mg deslorelin implant failed to reduce late embryonic losses when inserted on day 27 of pregnancy.