Bioactive supplements influencing bovine in vitro embryo development

Abstract

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.

Keywords: cytokines; embryo development; embryokines; growth factors.

Figure 1.

An example of how IL6 supplementation increases ICM cell number and the ICM:TE cell ratio in IVP bovine blastocysts. These data points represent blastocyst cell counts after differential cell staining for CDX2 (TE marker) and DAPI (DNA marker). Panel A shows ICM cell numbers and Panel B shows the ICM-TE ratio from a set of 5 independent studies. Each data point in both figures represents an individual blastocyst (n = 151 for control group and 156 for IL6-treated group). Overall means and SEMs are indicated by the bars. The different superscripts indicate differences (P < 0.05). This graph is taken with permission from Wooldridge and Ealy (2019).

Figure 2.

A summary of embryokines with documented positive effects on blastocyst development, embryo survival, including cryosurvival, ICM development and/or specification, and TE development.