Bioactive supplements influencing bovine in vitro embryo development

Ovum pickup and in vitro production (IVP) of bovine embryos are replacing traditional multiple ovulation embryo transfer (MOET) as the primary means for generating transferable embryos from genetically elite sires and dams. However, inefficiencies in the IVP process limit the opportunities to produce large numbers of transferable embryos. Also, the post-transfer competency of IVP embryos is inferior to embryos produced by artificial insemination or MOET. Numerous maternal, paternal, embryonic, and culture-related factors can have adverse effects on IVP success. This review will explore the various efforts made on describing how IVP embryo development and post-transfer competency may be improved by supplementing hormones, growth factors, cytokines, steroids and other bioactive factors found in the oviduct and uterus during early pregnancy. More than 40 of these factors, collectively termed as embryokines, are reviewed here. Several embryokines contain abilities to promote embryo development, including improving embryo survivability, improving blastomere cell numbers, and altering the distribution of blastomere cell types in blastocysts. A select few embryokines also can benefit pregnancy retention after IVP embryo transfer and improve neonatal calf health and performance, although very few embryokine-supplemented embryo transfer studies have been completed. Also, supplementing several embryokines at the same time holds promise for improving IVP embryo development and competency. However, more work is needed to explore the post-transfer consequences of adding these putative embryokines for any adverse outcomes, such as large offspring syndrome and poor postnatal health, and to specify the specific embryokine combinations that will best represent the ideal conditions found in the oviduct and uterus. This review provides an overview of how bioactive oviductal and uterine factors may influence in vitro embryo production in cattle. Deciphering the specific factor or factors that will improve embryo production and post-transfer pregnancy retention are envisioned to further propel the usage of ovum pickup and in vitro embryo production for producing genetically elite calves. Lay Summary Ovum pickup and in-vitro production (IVP) of bovine embryos have quickly become commercial options for generating large quantities of transferable bovine embryos from genetically elite sires and dams. However, 2 limitations in this process still exist. First, the percentage of eggs/oocytes that become fertilized and produce transferable embryos remains low. Second, IVP embryos that are transferred to recipients are less able to maintain a viable pregnancy than embryo produced by other means. Various maternal, paternal, embryonic, and culture-related factors will influence IVP success. This review describes how both IVP embryo development and post-transfer embryo competency may be improved by supplementing hormones, growth factors, cytokines, steroids, and other bioactive factors found in the oviduct and uterus during early pregnancy. These factors are collectively termed as embryokines. Several embryokines will promote IVP embryo development, but only a few of these embryokines have been tested for their ability to improve post-embryo transfer pregnancy retention. More work is needed to explore the post-transfer consequences of adding embryokines. However, with that being said, all indications are that we are on the right track with identifying one and likely several embryokines that will improve IVP embryo development and post-transfer pregnancy retention in cattle.