Understanding starch digestibility inside and out

Posted on August 11, 2015 in Dairy Performance
By Pat Hoffman
We feed lactating cows starch sources that may be ground, flaked, processed, rolled or ensiled.  In addition, we store feeds containing starch in bags, bunkers and bins at different moisture contents for different lengths of time.

With all these possible combinations, figuring out starch digestibility in the feeds we put in front of cows can seem like a daunting task.

In the last five years, scientists from out land-grant universities have taken a bit of mystery out of the equation.  It seems – regardless of the starch source – the key to figuring out digestibility is to understand how starch is protected inside and out…literally.

Outside protection of starch
Almost all the starch we feed to dairy cows comes from seeds and their seed coats have some fascinating properties related to digestibility.  For example, the seed coat of corn is poorly digested because rumen bacteria cannot attach to it.  Furthermore, enzymes that degrade starch cannot degrade the seed coat.

This is why we grind or process corn.  The goal is to reduce the effects of outside protection of starch by breaking apart the seed coat.

We also reduce outside protection via kernel processing in corn silage.  New kernel processing rolls are fitted to corn silage chopping equipment.  Early research data from these new roll types suggests better kernel processing while increasing forage particle length.

Inside protection of starch
In all seeds, starch is encapsulated in waterproof proteins called prolamins.  These prolamins break down during fermentation, but it’s a slow process.  Starch digestibility of feeds like corn silage and high-moisture corn (HMC) will improve dramatically with advancing fermentation time.

However, research has clearly defined the process is slower than originally hypothesized and – even worse – if corn silage or HMC is too dry, it may take more than a year to improve starch digestibility to a desired level.

Using the information available
Our feed and forage testing laboratories have great tools such as seven-hour in-vitro starch digestibility, mean particle size or fecal starch analysis to help tailor our rations for lactating dairy cow diets.

In addition, following these simple “rules of five” also help us understand and optimally utilize starch in our dairy rations:

  • Dry shelled corn should be ground to 500 microns;
  • Corn silage should be processed to a CSPS score of double the dry matter minus 5 (DM x 2 –5)
  • Corn silage and HMC starch feeds best when it has been stored for 5 months
  • Highly digestible HMC has an ammonia content greater than 5 percent of the crude protein
  • Feeding snaplage that has been stored longer than 5 months may reduce butterfat test
  • Corn silage and HMC starch is highly digestible when soluble protein is greater than 55 percent

This article was originally written for the May 7 edition of Progressive Dairyman.

Category: Dairy Performance
Feed quality and nutrition