Watch for Changing Starch Digestibility


By Bill Mahanna, PhD, Dipl. ACAN, Pioneer Global Nutritional Sciences Manager

The era of higher corn prices has many nutritionists looking at feeding elevated levels of corn silage as a way to reduce starch input costs. High-moisture corn (HMC) is also making a resurgence in areas that have more recently relied on feeding purchased corn meal.

Coupling HMC with corn silage inclusion rates exceeding 15 lb. of dry matter per day has proven to be the foundation of economical rations on many dairies. However, some dairy producers have reported loose manure and erratic intakes among lactating cows fed long-stored corn silage and HMC with no readily apparent changes in nutrient content of the ration components. Research results are now shedding light that digestibility changes over time in storage may be an underlying cause of these mysterious feeding problems.

An early understanding of this phenomenon was provided by University of Nebraska graduate student J.R. Benton and coworkers (2004), who conducted in situ dry matter digestibility (ISDMD) research comparing dry-rolled corn with the same hybrid ensiled as HMC at moisture levels ranging from 24 to 35%. ISDMD was conducted on samples at 28- day intervals out to at least 298 days in storage.

Dry-rolled corn and the lowest-moisture HMC (24% moisture) did not change significantly over time in storage, delivering a relatively stable digestibility profile as desired by many nutritionists. However, all HMC treatments resulted in a higher ISDMD than the dry-rolled grain, apparently as a result of the fermentation process. The largest changes in HMC ISDMD occurred during the first 28 days of ensiling, with linear changes post-28 days ensiled.

The rapid changes observed during the first month of storage support the commonly endorsed recommendation of providing HMC (or corn silage) one to two months of fermentation before feeding. However, what was not previously well documented was how the wetter HMC treatments continued to change in ISDMD for an entire year in storage. Results show that ISDMD increased from day 60 to day 289 by 8- 30% depending upon the kernel ensiling moisture (Figure).

Chart: Changes in HMC in situ dry matter digestibility over time in fermented storage

The researchers theorized that with 24% moisture corn being close to the average in the beef industry, ISDMD could be improved by increasing corn moisture and length of ensiling for enhanced feeding value and improved cattle performance. They cautioned that higher-moisture corns would likely require more management.

Given current grain prices, ensiling higher-moisture corn could also be economically significant in dairy rations if it is possible to monitor and adapt rations to changing digestibility caused by length of time in storage.

I have personally experienced field situations that parallel the Nebraska research. The results of a newly available, 12-hour in vitro ruminal starch digestibility analysis (Dairyland Labs, 2006) showed an increase from 68 to 85% for 27% moisture HMC ensiled for 60 versus 240 days, respectively. Increases of this magnitude could explain some of the “spring acidosis” observations, given that most nutritionists do not adjust the energy density of fermented feeds based on the length of time in storage.

Newbold et al. (2007) reported research on changing starch digestibility in corn silages stored in bunker silos in the Netherlands. The proportion of starch degraded after three-hour in situ incubations increased significantly (P < 0.001) with storage time with a mean of 53.2% at two months to 69% at 10 months of storage.

There was an interaction between effect of storage time and dry matter of the corn silage at ensiling (P < 0.001). The increase in three-hour degradability between two and 10 months of ensiling was 0.7% for silages less than 30% dry matter and 25% for silages greater than 37.5% dry matter. These researchers concluded that the effect of time since ensiling on starch degradability should be considered in ration formulation. Owens (2007) has proposed that length of fermentation exerts influence primarily from ethanol solubilizing zein protein along with acid hydrolysis of other kernel proteins that may interfere with starch granule degradation. It is interesting to note that in the Nebraska HMC research, slopes representing changes in degradable intake protein for post-28-day ensiled samples closely paralleled the ISDMD slopes. In the Newbold corn silage study, crude protein degradation also increased with time in storage but was not highly correlated (P > 0.1) with starch digestibility.

This lends support to why feedlot nutritionists routinely use water-soluble nitrogen analysis as a predictor of acidosis risk when feeding HMC. Many consider values between 50 and 60% water-soluble nitrogen (expressed as a percent of total nitrogen) as ideal for This lends support to why feedlot nutritionists routinely use water-soluble nitrogen analysis as a predictor of acidosis risk when feeding HMC. Many consider values between 50 and 60% water-soluble nitrogen (expressed as a percent of total nitrogen) as ideal for feedlot rations, whereas values greater than 60% indicate corn that will likely have very rapid ruminal starch digestion. Values less than 40% indicate that the acidosis will not be a big concern (Soderlund, 2007).

Perhaps dairy nutritionists should start tracking water-soluble nitrogen levels as a proxy for ruminal starch degradability.

The Bottom Line

Research findings are starting to put credence to field experiences suggesting starch and protein degradability increase over time in both HMC and corn silage. However, the effect of fermentation should not be viewed as an acceptable alternative to adequate pericarp damage from proper processing of HMC or corn silage.

Using newly available starch digestibility laboratory methods or perhaps tracking water-soluble nitrogen levels may help nutritionists monitor these changes. Ensiling higher-moisture corn grain can improve corn grain feeding value but must be managed more carefully from both an ensiling and feeding perspective. It may be helpful to collect and freeze samples that have fermented for 30-40 days to benchmark against samples fermented for a longer time (e.g., 200 days).

Understanding these changes can help nutritionists better formulate cost-effective rations as well as prevent potential acidosis problems caused by longer-fermented feeds.


Benton, J.R., T.J. Klopfenstein and G.E. Erickson. 2004. In situ estimation of dry matter digestibility and degradable intake protein to evaluate the effects of corn processing method and length of ensiling. J. Dairy Sci. 87 (Suppl. 1):936 (abst.).

Dairyland Labs. 2006. Cow relevant digestibility, dry matter, starch and NDF. Accessed at interpretations/cowrelevantdigest.php.

Newbold, J.R., E.A. Lewis, L. Lavrijssen, H.J. Brand, H. Vedder and J. Bakker. 2006. Effect of storage time on ruminal starch degradability in corn silage. J. Dairy Sci. 89 (Suppl. 1):T94 (abst).

Owens, F.N. 2007. Personal communication.



This article was originally published in June 2007 Feedstuffs issue, and is reproduced with their permission.