Individual values for pyruvate consumption by bovine embryos assigned to tertiles on the basis of their pyruvate consumption and the resultant blastocyst rates.

<p>Tertile 1 (T1) are the cohort of embryos with low rates of pyruvate consumption (1.14±0.02 pmol/embryo/h); Tertile 2 (T2) are the embryos with an “intermediate” (6.14±0.27 pmol/embryo/h) level of pyruvate consumption and Tertile 3 are the embryos with high pyruvate consumption (13.00±0.48 pmol/embryo/h). Categories of activity, according to the Dynamic Energy Budget Theory are overlaid. According to this theory, we propose that for any given substrate, there is an optimum level of metabolism, and that this optimum varies temporally to meet the demands of growth and development at each stage. In the case of an early embryo, we propose that when exposed to a challenge or stress, the resulting response will have an energy cost. This cost may be met by an increase depletion of a given substrate to fuel the additional activity, or indeed may lead to a partitioning of substrates away from essential processes. In either case, a shift out of the optimum range leads to the early embryo having a <i>pejus</i> metabolism, indicating sub-viability. The early embryo in this stage of metabolism may be able to rectify the stress and return to optimum metabolism and continue development, however if further resources are needed, the embryo may be further compromised as indicated by a <i>pessimism</i> metabolic phenotype; in this case, very low or very high metabolic activity indicative of sub viability.