where V PDH denotes flux through pyruvate dehydrogenase; V CS denotes flux through citrate synthase; V PK denotes flux through pyruvate kinase; V ME, out denotes flux through malic enzyme from malate to pyruvate; V ME, in denotes flux through malic enzyme from pyruvate to malate; and V PC denotes flux through pyruvate carboxylase. Additional fluxes shown in the complete flux diagram in Fig. 1 are V GNG OAA gluconeogenesis from oxaloacetate, V GNG total gluconeogenesis, and V prop the rate of propionate entry into the TCA cycle. V PDH / V CS was measured using the ratio [4- 13 C]glutamate/[3- 13 C]alanine, as described by Alves et al. ( 11 ).
In 2010, enteric fermentation accounted for 43% of the total greenhouse gas emissions from all agricultural activity in the world,  26% of the total greenhouse gas emissions from agricultural activity in the ., and 22% of the total . methane emissions.  The meat from domestically-raised ruminants has a higher carbon equivalent footprint than other meats or vegetarian sources of protein based on a global meta-analysis of lifecycle assessment studies.  Methane production by animals, principally ruminants, is estimated 15-20% global production of methane, unless the animals were hunted in the wild.