Effects of hormonal treatments on reproductive performance and embryo production

Developments in the use of drugs to improve reproduction and embryo product ion have focused on estrus and ovulation synchronization protocols and embr yonic survival. Protocols for synchronization of ovulation eliminate the ne ed for detection of estrus and allow timed insemination of all cows enrolle d. Various estrogenic, progestational, GnRH and PGF(2 alpha)-like drugs are used to synchronize follicle development, CL regression and induction of o vulation. Strategies are discussed to optimize such programs to maximize he rd pregnancy rates. Use of bovine Somatotrophin (bST) in combination with t he Ovsynch protocol resulted in increased pregnancy rates, indicating possi ble effects on oocyte and embryonic development. Treatment of embryo donor cows with bST reduced the proportion of unfertilized oocytes and increased the number of transferable embryos. Furthermore, bST increased pregnancy ra te when given to the recipient. Sub-luteal plasma progesterone concentratio ns after insemination have been associated with lower pregnancy rates. Inje ction of hCG on day 5 post-insemination resulted in induction of an accesso ry CL, increased plasma progesterone concentrations and increased conceptio n rates. Strategies involving the use of sustained GnRH agonists to enhance CL development and alter follicular development are considered for future programs to enhance pregnancy rates. (C) 2000 by Elsevier Science inc.