C:B1 and C:B3 Kd (%/hour)
Carbohydrate pool specific digestion rates (Kd) are the calculated maximum rates of degradation per hour for the B1, B2 and B3 carbohydrate pools as defined by models like CNCPS or CPM. It should be recognized that strict definitions of B‐pool constituents (e.g. B1 is only starch) cannot be adhered to with this type of analytical tool given the heterogeneous nature of nutrients which can exist in both the fast and slow pools. However, FermentricsTM B‐pool rate estimates do allow nutritionists more realistic values than the “book values” contained in feed libraries or NDF digestion rates calculated from NDF, lignin and single time‐point NDFD. FermentricsTM captures over 5,000 gas data points in the 48‐hour incubation. This allows curve peeling software to detect fast pool and slow pool terminal rates from the inflection points in the total gas curve. Digestion rates are reported as normalized specific rates and not actual rates, therefore, you can have a high number if you have a small pool and a fast actual rate. Specific rates equal the terminal rate divided by the pool size (e.g. the gas produced by each pool). Large pools with the same actual rate will have smaller specific rates. See example:
Field experience suggests that B3 (NDF) pool rates of less than 5% per hour are reflective of low digestibility forages resulting in reduced energy intake and microbial protein production. Depending upon the gas volume produced by the fast pool, increasing the supply of NFFS may be a solution to drive more production (see more detail in section entitled “Relative Proportion of Pools”).
Chai et al., (2003) published equations for starchy feed ingredients and corn silage (Not TMR’s) describing the relationship between gas levels and measured starch degradation. This allows for redefining the fast pool into B1 (starch) and B2 (soluble fiber) for better defining feedstuff kinetics in ration‐balancing software.
Field experience suggests that B1 pool rates in excess of 25%/hour are indicative of situations where the potential for ruminal acidosis, fat/protein inversions and poor hoof health exists. Rates that are slower could be reflective of feeding dry corn versus fermented corn and can be lower yet in the rumen if processing of kernels in the corn silage is poor, or if the grain is not adequately processed (700‐1200 microns; low end for dry corn and higher end for HMC). Fermentrics samples are ground to 6‐mm so the starch particles will be very fine and particle size of on‐farm feedstuffs can further reduce fast pool rates.
