Starch Digestibility Changes in Storage

Research shows digestibility changes over time in stored corn silage or high-moisture corn (HMC) may be an underlying cause of mysterious feeding problems on some dairies, reports Bill Mahanna, Ph.D., DuPont Pioneer Global Nutritional Sciences Manager.

It is becoming increasingly common to feed high levels of corn silage to provide a consistently digestible fiber source and to reduce starch input costs. When coupling high levels of corn silage with fermented high-moisture corn, some dairies have noticed loose manure and erratic intakes in lactating cows starting in late winter to early spring despite no obvious changes in nutrient content of the ration.

Research has now shown that the starch in fermented corn silage and HMC increases in digestibility over time in storage. Mahanna cites some examples:

  • A University of Nebraska study was one of the first studies to point out that the digestibility of HMC continued to increase throughout 12 months of storage. They showed that kernel dry matter disappearance (mostly starch) increased from day 60 to day 289 by 8% to 30% depending on the kernel moisture at ensiling.

  • A 12-hour in vitro ruminal starch digestibility analysis (Dairyland Labs, 2006) showed that 27% moisture HMC increased in 12-hour starch digestibility from 68% after 60 days to more than 85% after 240 days in storage.

  • Research in 2014 from the Netherlands found that corn silage starch degradability increased from 70.8% at harvest and stabilized at 86.3% at eight months of ensiled storage. Higher dry matter silages (40% dry matter) showed lower initial harvest starch degradability (61.3%), which also increased over time to stabilize at 78% at eight months of storage.

  • More 2014 research from Virginia Tech investigated how storage time of two corn hybrids bred for varying amounts of floury and vitreous starch affected starch degradation rates. While differences existed in fresh silage at harvest, there were no differences for any starch digestibility parameter between the two endosperm types when measured after 54 days of storage. Although there were no differences between hybrids of differing endosperm types, it does not change the fact that starch digestibility in corn silage does change over time in fermented storage.

The increase in starch digestibility due to the fermentation process should not be considered an alternative to proper processing of kernels at harvest.  Understanding changes in starch digestibility can help nutritionists better formulate cost-effective rations as well as prevent "spring acidosis" problems caused by longer-fermented feeds. However, most ration software does not adjust starch digestibility rates for either degree of kernel processing or length of time in storage.

To help manage changes in starch digestion rates, Mahanna suggests using newly available starch digestibility laboratory methods (e.g. Fermentrics or 7-hour starch digestibility) or perhaps tracking water-soluble nitrogen levels over time as they are highly correlated to increasing starch digestibility in fermented feeds.

The foregoing is provided for informational purposes only. Please consult with your nutritionist or veterinarian for suggestions specific to your operation.  Product performance is variable and subject to a variety of environmental, disease, and pest pressures. Individual results may vary.

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