A question that needs to be asked when thinking about starch digestibility when feeding high-producing dairy cattle is: “Do you want to feed the rumen bugs, or do you want to feed the wildlife?"
If you’re an avid hunter in search of big bucks or long-bearded turkeys, the latter might not sound so bad. When corn prices are hovering around $6 per bushel, it’s likely that you (and your cattle) would be better served feeding the rumen and leaving the wildlife to fend for themselves.
Starch, delivered as grain or silage, will be best utilized if it’s fermented in the rumen where the microbial population can utilize it for growth and energy production.
The impact of improving starch digestibility on lactation performance is well documented. Ohio State researchers showed that employing strategies to increase starch digestibility with corn grains can increase milk yield up to 5 pounds per head per day.
Wisconsin researchers showed that kernel-processing corn silage improved total tract starch digestibility by about three percentage points or more. Direct effects of kernel-processing corn silage on milk yield are not always consistent, as factors such as whole-plant moisture content come into play.
In general, responses to processing are often greater as whole-plant moisture decreases. When starch sources are all processed properly, manure starch content should be below 5 percent.
Here are some tips and considerations to help you optimize starch digestibility in this year’s harvest. The three main factors that influence starch digestibility from corn grain and corn silages are processing and particle size, maturity and moisture content, and time.
Processing and particle size
Processing corn grain and corn silage increases surface area so that microbial digestion can take place. The smaller the particle, the more complete digestion will be.
The recommended mean particle size for dry corn is 700 microns as a maximum. The guidelines for high-moisture shelled corn (HMSC) become less concrete.
The drier the HMSC, the finer the grind needs to be. A mean particle size of 1,200 to 1,500 microns is recommended for HMSC at 30 percent moisture. Occasionally check dry corn particle size with a feed testing laboratory to make sure targets are being met.
Chopping corn silage at shorter lengths of cut will improve kernel processing, but rumen health could be compromised due to a lack of physically effective fiber from stover. Likewise, just “nicking” the kernel is not good enough.
Monitoring for proper kernel processing during harvest is needed. This can be done by scooping up a quart of fresh corn silage and separating out all the half and whole kernels.
If you find more than two, processing is inadequate. Talk with the chopper operator, as it’s likely that roller speed differential, roll gap or harvest speed are not correct.
Mention must be made of shredlage. Though much is yet to be discovered, this next crop year and pending research are sure to bring new information and guidelines for adopting this new technology.
Research and field experience so far show promise that this is an effective method to process not just corn kernels, but cob and stover as well, while maintaining rumen-friendly length of cut.
Proper processing and particle size with snaplage has been difficult to nail down due to the amount of husk that is often present. The goal is to have as little long “trash” and cob present as possible and complete kernel destruction.
Experiences so far indicate that chop length should be set as short as possible and roll clearance at 2 to 3 mm with a 30 to 40 percent speed differential.
Maturity and moisture content
Remember the old recommendation that corn silage should be harvested at black layer?
Research and experience has now shown that waiting until black layer can result in silage that is too dry for kernels to be well utilized, as there is considerable variation in the relationship between whole-plant moisture content and kernel milkline position.
Plant hybrid differences and growing conditions can have a large impact in how corn plants mature and kernels dry down. The focus now is on whole-plant moisture content.
Once the milk line is visible and most of the kernels are dented, it’s time to chop some whole plants to measure moisture content.
Once whole-plant moisture reaches about 70 percent, it is about time to get chopping on the most mature fields if bunkers are the destination. If bags and uprights are the storage selection, 65 percent whole-plant moisture is a good target.
Take into consideration weather at harvest time. If the week of harvest is hot and dry, corn plants can lose well over a point in moisture per day. Typically the best lactation performance and starch digestibility have been show to occur between 65 to 70 percent whole-plant moisture.
Target 28 to 32 percent moisture for HMSC. Check multiple fields and scout for fields that could be drying the fastest. For optimum starch digestibility, a little too wet is better than too dry.
If you are going to start feeding HMSC immediately after harvest, you may want to consider segregating two to three months’ worth of HMSC that is harvested at higher moistures, in the 36 to 40 percent range.
While this definitely may not follow “conventional wisdom,” this practice has served many producers well as it provides an immediate source of highly digestible starch while other sources are fermenting.
Snaplage does seem to follow the old black-layer adage. At this stage, kernels are physiologically mature and will be around 34 to 36 percent moisture.
This should result in a final moisture content in the mid-30s to low 40s. The harvest window for snaplage can be pretty narrow, so if you are going to err, it’s best to be on the wet side and not be over-dry.
Time
Time is a great ally in improving starch digestibility. You’ve probably experienced the phenomenon that as corn silage and HMSC age, they seem to “feed better.” On the flip side, when young corn silage replaces aged corn silage soon after harvest, milk yield often drops.
Several controlled studies have shown that starch digestibility for both corn silage and HMSC improves dramatically with time ensiled.
It’s been shown that this increase in starch digestibility over time is due to the presence of protease enzymes that break prolamin-zein protein subunits, which hold starch granules together. Prolamin-zein proteins encapsulate corn starch and act as a barrier to digestion.
The implication here is to have an ample corn silage inventory so carryover lasts into January or February of the following year. After four to five months, starch digestibility in corn silage should be approaching its maximum.
In regards to HMSC, carryover is definitely a good idea. However, the issue of practicality comes into play as research has shown that at eight months to over a year in storage, HMSC digestibility is still improving.
The importance of achieving optimal starch digestibility can be shown with some simple but realistic napkin math. Let’s assume a 26 percent starch diet is being fed to cows consuming 57 pounds dry matter intake.
If total tract starch digestibility was improved by 10 percent, 1.5 pounds of starch dry matter would no longer be passing through the cows.
Equating this to dry corn equivalents at $6 per bushel for corn, this 1.5 pounds dry matter starch has a value of $0.27 per cow per day. And we have not even accounted for any possible gains in lactation performance.
So as this year’s “starch harvest” approaches, make sure all is in place to ensure starch is as digestible as it can be. Although the wildlife might not like it, your cows and your wallet will. PD
References omitted due to space but are available upon request. Click here to email an editor.
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Eric Schwab
- Dairy Nutritionist Technical Services
- Vita Plus Corporation
- Email Eric Schwab
