Starch content and digestibility drive corn silage utilization

by Allen Wilder

CORN silage is a cornerstone of modern livestock nutrition, providing a highly nutritious and energy-dense feed option. Corn silage starch plays a critical role in meeting the energy requirements of livestock. Therefore, optimizing starch at harvest is essential for maximizing the nutritional value and performance of dairy and beef cattle.

Kernel processing is a pivotal component in unlocking the full potential of corn silage starch. Kernel processors break or crack the corn kernels at harvest, thereby enhancing starch accessibility during animal digestion. Proper kernel processing enables livestock to more efficiently utilize starch, leading to improved nutrient utilization and animal performance.

Unleashing energy potential

Most modern forage harvesters are equipped with specialized processors that crush kernels between two abrasive steel cylinders. These rollers rotate at different speeds, which enhances kernel size reduction. The roller gap can be changed to adjust the aggressiveness of the processing during harvest. The cost of a gap that is too wide is lost starch out the back of the cow. Too narrow a gap might cost you extra time and fuel at harvest. Current guidelines suggest that a gap setting of 1 to 3 millimeters (mm) is optimal for most conditions.

While kernel processing makes starch accessible by exposing more kernel surface area, the digestibility of corn silage starch is the metric that determines how quickly accessible starch is degraded by microbes. The worst scenario is to have corn silage with large pieces of kernel that are low in digestibility. There are many factors that can impact starch digestibility and understanding them is important to optimizing starch digestibility and harnessing the full energy potential of corn silage.

Grain maturity: Harvesting corn silage at the ideal grain maturity stage is crucial for maximizing starch digestibility. As corn kernels mature, starch content rises, but its digestibil- ity declines. By harvesting corn silage at the 1/2 to 3/4 milkline, a balance is struck between starch content and digestibility. Harvesting too late impairs digestibility, but harvesting too early lowers yield and whole-plant digestibility due to a lower starch concentration. Hybrid selection: Since kernel composition is largely genetic, the choice of corn hybrid significantly affects starch digestibility. More specifically, kernels that genetically express greater amounts of floury starch tend to be more digestible than kernels that produce the hard, vitreous starch characterized by flint corn. Advances in genetic selection have led to the development of hybrids with superior starch digestibility traits. Some of these hybrids even have a recessive trait that results in kernels that are completely composed of floury starch. The downside is that these hybrids tend to produce lower overall starch content as compared to conventional dent corn.

Moisture content and fermentation time: Plant moisture content at harvest is a critical factor influencing starch digestibility. Not only does it relate to kernel development, but adequate moisture is required for fermentation processes to occur that stabilize the silage for storage and feedout. These processes also have the effect of enhancing starch digestibility over time. Thus, silage that is overly dry or fed out within several months of harvest is more likely to suffer from poor starch digestibility. The optimal silage moisture content is around 65%.

The question of how to assess the quality of starch in silage has been highly debated over the years. The obvious gold standard is to feed the silage to cows and measure the actual starch utilization by the animal. While that works from a research standpoint, it isn’t too practical for the average farmer seeking to produce better feed.

Most farmers and nutritionists would have corn samples analyzed for 7-hour starch digestibility and perhaps kernel processing score. Measures of starch digestibility can be informative, but in vitro measures of starch often yield inconsistent results. Even the more precise assays available give an incomplete picture by failing to account for particle size. The current methods for determining the kernel processing score do

Effect of corn hybrid kernel type and roll gap on starch metrics over time Relative

provide a measure for starch particle size, but this measure doesn’t account for differences in kernel composition.

A new measure

A new metric for assessing the quality of silage starch was recently evaluated in a study at the Miner Institute in Chazy, N.Y. The assay has been termed “soluble starch” by the forage-testing lab that developed it, but it is really just a measure of the washout fraction of starch that easily moves out of the sample when water is added.

The exciting part about this new measure is that it appears to integrate both particle size and digestibility into a single number, providing an assessment that could correlate well with animal response. Our study results showed that soluble starch increased with fermentation time and was higher with a floury kernel type (Figure 1). This is the very same pattern that was observed with the starch digestion rate (Kd) measured in the study. Furthermore, a slight adjustment to the processor roller gap resulted in a measurable difference in soluble starch in unfermented samples.

Optimizing corn silage starch at harvest is a vital consideration for maximizing the energy potential and nutritional value of corn silage. Effective kernel processing, which is achieved with modern equipment and proper adjustment, plays a pivotal role in enhancing starch availability. Alongside kernel processing, other factors such as grain maturity, hybrid selection, moisture content, and length of fermentation significantly impact starch digestibility.

Optimizing these factors leads to improved energy utilization, feed efficiency, and performance for animals on corn silage diets. Utilize the best indicators available to make informed decisions about starch quality. Harnessing the power of corn silage starch sets the stage for enhanced profitability and sustainability. •

by Paul Dyk

IT’S the new “sexy” forage, also known as the cocktail mix; it’s mysterious, unknown, and risky. She is a femme fatale. Seductive, she draws her lover into a compromised relationship. Once she is planted, there are many promises — but no guarantees. Dramatic? Perhaps, but before you start dating this forage, be ready for a rocky relationship with highs and lows.

The cocktail mix moniker is, of course, unspecific. In the field, we think of a cocktail as a mix of warmand cool-season annual grasses and legumes. With such a generic, although alluring, name, it’s not surprising that cereal forages, clovers, sorghums, ryegrasses, and other species all come into play. By planting a mix, it is hoped to take advantage of various growing conditions. In some cases, yields in excess of 4 tons of dry matter per acre have proven to outperform alfalfa.

Have eyes wide open

Following are some considerations that will help you better understand this new relationship and ensure that cocktail mixes meet your expectations.

■ Forage quality and yield: I have seen the Twitter post documenting a relative forage quality (RFQ) of 240 for a cocktail mix. There are four questions that must be asked regarding such a claim:

1. What was the cost per ton of dry matter? Lost in the discussion at times with various alternative forages is the actual cost. If five to six cuttings are harvested, the tractor and equipment are driven across the field five to six times. How does this influence the actual cost per ton of dry matter averaged across the year?

2. What was the yield? Regardless of whether you have an annual grass, alfalfa, or corn silage, there is always the balance of quality versus yield; you need a certain number of tons for forage (and fiber) to feed cows for an entire year.

3. Do you want to feed rocket fuel? Forage that is extremely high in quality can work in some diets, but it likely cannot be the sole forage; cows have a need for undigestible forage (undigestible neutral detergent fiber [uNDF]) to maintain proper rumen function.

4. Is this repeatable? One Twitter post from a random farmer doesn’t tell you if this will work on your farm with your soil conditions in both a wet or dry year.

■ Seasonal flux: Most farms might have some fields planted to a cocktail mix while maintaining alfalfa in others — call it risk management or a lack of commitment to the relationship. This leads to a fundamental flaw in the system; namely, there becomes a lack of synchronicity between your alfalfa forage cuttings and the cocktail cuttings. How do you manage four cuttings of alfalfa and multiple cuttings of the cocktail mix? One strategy is to store the cocktail mix separately. On large dairies, bunker and pile space is at a premium; multiple cuts are then stored in front of other cuts, leading to more frequent changes in forage quality.

Storing cocktail forages separately in bales or bags can be an option, but this invariably leads to inconsistent feed coming out of storage. I think there are two reasonable options to help solve this issue. First, if possible, time the cuttings to coincide with your alfalfa and layer the forages in the bunker or pile, even though yield might be compromised slightly to sync cuttings.

Layering isn’t pretty, but it can be effective. Packing and more packing is critical. If a quality facer is used, and the forage is pushed and “mixed” adequately with a bucket, a forage mix can be fed that is consistent day to day and will change slowly over a longer period of time. Cows (and nutritionists) thrive on consistency. If the same bunker of feed can be fed for four months, there is time to make small adjustments based on cow response. If forages are switched every four to six weeks, then there is a need to constantly “chase” the cow response. Second, if the feed is stored in bags or small piles, use this forage at a low feeding rate (less 5% of dry matter) to limit the effect of variability on the cow.

■ Allocation of forages: With cocktail mixes, there will certainly be times when the quality does not meet high-producing cow standards. Faroff dry cows and bred heifers can be a great place to allocate these forages. However, for farms without heifers, it is easy to become heavy on a forage that has a limited need.

■ Consistency: Most nutritionists are not in love with the sexy cocktail mix but rather prefer her bland looking sister — corn silage. While we argue with each other over brown midrib and conventional hybrids, we mostly enjoy the stability in the corn silage relationship because we generally know what to expect. Yields and quality vary with corn silage, too, but there is usually just one change a year. For the highest producing herds, consistency is often the common theme. Will a cocktail mix work in your system to maintain this consistency?

■ Harvest targets: Harvest targets for corn silage and alfalfa are well established. Alfalfa scissors clippings and fall dry-down reporting for corn silage have become standard practices in many areas. But what is the target for cocktail mix blends?

For alfalfa, we often target 33% to 36% NDFom. For some grass blends, this is far too low. A high-quality grass with high fiber digestibility might have an NDFom of 42% to 44%. One option is using a combination of aNDFom and uNDF240 (undigestible fiber) with a target of 48% to 52%. For example, alfalfa at 34% NDFom and 16% uNDF240 has a combined value of 50; grass forage at 44% NDFom and 7% uNDF240 would have a combined value of 51. Using the 48% to 52% combination parameter might be helpful in evaluating timing of harvest across multiple, variable fields. I’ve seen combined forage bunker silos with 40% NDFom and 10% uNDF240 that fed well.

Starting a relatively new relationship with a sexy forage can work, but keep your eyes wide open to the potential for variable yields and forage quality. •