Go beyond crude starch
Oct 02, 2013
The starch content of feeds can often be quite variable.
A look at corn silage samples collected from across the U.S. over a five-year period between 2007 and 2012 shows crude starch varied from 2 percent to 58 percent with an average of 30 percent.
While this is problematic on several fronts, it gets more complicated. That’s because the starch available to rumen microorganisms also can be inconsistent, and that means the starch available to the cow also will be variable.
During the same five-year period, rumen digestible starch scores of corn silage samples ranged from 1 to 10.3 with an average of 7.8. A low score indicates the starch is slow-digesting. A high score indicates a fast-digesting starch.
Variability in the starch available to the cow can be problematic to performance. On one hand, excessive amounts of digestible starch can have negative consequences on fiber digestibility in the rumen, as well as energy metabolism, dry matter intake and milk and milk fat production. On the other hand, if starch is less available in the rumen, it will not adequately support propionic acid production in the rumen. Ultimately, this has ramifications on lactose synthesis, which has a direct impact on milk production.
Keeping the pendulum from swinging too far in either direction can be a challenge. Fortunately there is help for managing the effects of starch variability, but it involves more than simply knowing and adjusting for crude starch levels in a feed. It also involves unlocking what’s going on with starch in the rumen.
Relying solely on the crude starch content of ingredients to formulate rations is simply not enough anymore. You need an accurate, predictable estimate of how degradable starch and fiber are in the rumen. Testing for rumen digestible starch and fiber gives you the knowledge to make ration decisions more effectively.
In vitro ruminal digestibility of starch from corn silage samples collected across the U.S. varies both within and among years. Data from Calibrate® Technology Lab, 2013, Gray Summit, MO