A simple salt solution medium supplemented with yolk plasma and lactate (YPLM) supports development of preimplantation bovine embryos in vitro

This study investigated the embryotropic potential(s) of egg yolk (EY) or its fractions, yolk plasma (YP) and yolk granules (YG), in culturing bovine embryos in vitro and substituting for protein (FCS, BSA, and BME-E and MEM-NE amino acids) and energy (glutamine, pyruvate and L-lactate) supplements commonly added to culture medium. In the first set of experiments (Experiment 1, 2 and 3) CR1aa with buffalo rat liver (BRL) cells were used as a co-culture system. The addition of 2.5% or 5% EY significantly increased (P<0.05) blastocyst percent over the BRL control (48.3% and 52.4% vs. 32.5%, respectively). The addition of 5% EY in the absence of FCS and BSA resulted in percent development to blastocysts and hatched blastocysts similar (P>0.05) to those of the BRL control (37.6% and 57.4% vs. 51.5%, 22.7% and 39.5%, respectively). The supplementation of the BRL control with 5% YP compared to that of EY resulted in comparable (P>0.05) percentages of blastocysts and hatched blastocysts (39.0% and 51.6% vs. 40.0% and 58.3%, respectively). In the second set of experiments, the embryotropic potential of YP was examined using a cell-free culture system and a simple salt solution (SS) of NaCl, KCl and NaHCO3 as the base medium. The supplementation of an energy-supplemented cell-free simple salt solution (E-SS) with 5% YP in the absence of supplemental protein resulted in percent development into blastocysts and hatched blastocysts comparable (P>0.05) to those of a BRL control (39.2% and 15.8% vs. 37.1% and 22.2%, respectively). The addition of YP to the simple salt solution with hemicalcium L-lactate as the only supplemented energy ingredient resulted in percentages of blastocysts and hatched blastocysts similar (P>0.05) to those obtained by the supplementation of all energy sources (27.4% and 15.6% vs. 36.4% and 14.0%, respectively). Increasing hemicalcium L-lactate level from 5 to 10, 20 or 25 mM resulted in a significant decrease (P<0.05) in percent development into blastocysts (36.5% vs. 24.8%, 11.6% and 6.7%, respectively). In conclusion, YP, with the advantage of being clearer than EY, is capable of sustaining embryo development to the blastocyst stage in a simple salt solution of NaCl, KCl and NaHCO3 supplemented with hemicalcium L-lactate.