aPartitioning Factor

Apparent partitioning factor is a good indicator of the fermentation efficiency and is calculated as: (short chained VFA yield + microbial protein production)/total gas production. A higher aPartitioning Factor value indicate less gas and more ATP for increased microbial growth. As a general rule, higher levels of gas production indicate higher levels of acetate production which in turn results in lower ATP production.

The main VFA’s produced during the fermentation are propionate, acetate, and butyrate. These VFA’s produce different levels of ATP (energy) per mole; propionate 3, acetate 2, and butyrate 2. They are also associated with different levels of gas production with high acetate fermentations producing more gas (methane and C02) compared to high propionate fermentations. Blummel et al., (1997) published research on the relationship between gas from the production of SCFA and microbial biomass yield. He found an inverse relationship between gas production and microbial biomass yield when the variables were related to a given unit of truly degraded substrate. This is due to higher gas production when SCFA like acetate are produced compared to the ATP energy available for microbial growth when propionate is produced. Blummel proposed the concept of a partitioning factor (PF) which is the ratio of truly degraded substrate to gas volume produced. Interestingly, forages with a high PF (e.g. low gas production per unit of truly degraded substrate) exhibited higher intakes. Their dry matter intake prediction model included rate and extent of 24‐hour gas production along with PF and accounted for 84% of the variation in the intake of fifty four forages in their research.

TMRs that produce a high partitioning factor (>4) are strongly associated with higher propionate fermentations which produce more ATP and support increased microbial protein production.