By Mike Rankin
Our understanding of corn silage has come a long way in the past 20 years. That’s probably a good thing because it has emerged as a dominant feed source in most dairy and many feedlot beef rations. What is being achieved with corn silage these days is entirely different than what your grandfather was able to accomplish . . . or even comprehend.
To draw from the old Certs breath mint commercials, corn silage is two, two, two feeds in one. Some argue it’s a grain, others a forage. In fact, the grain and forage portion of corn silage are nearly equally distributed on a dry matter basis.
From a nutritional standpoint, we’re essentially interested in corn silage as a source of starch (energy) and fiber, along with their respective digestibilities. Agronomically, yield is always a consideration, especially if land base is a limiting factor.
When trying to maximize the utilization of one component, there is often, but not always, a trade-off with the other component. Of course, trade-offs in the forage and feed industries are nothing new.
It’s a war on kernels
“If you don’t break kernels, it’s very unlikely you will be able to utilize the starch,” Luiz Ferranetto, a dairy nutritionist with the University of Florida, recently said at the Four-State Dairy Nutrition and Management Conference in Dubuque, Iowa.
There was a day when the prevailing line of thinking was to simply crack the kernel during harvest and the cow would do the rest. Hopefully, nobody is still in that camp.
These days, the ability to make great corn silage has morphed into a war on corn kernels where “obliteration” is the battle cry. Of course, technological advancements in kernel processors have made that happen along with the ability to measure kernel processing scores (KPS).
It’s become really simple from a goal standpoint: If you don’t do a good job of kernel processing, starch (corn kernels) will merely take up space in the manure spreader.
Let’s conclude this brief starch discussion with one more rock-solid axiom of starch digestibility brought forth by Ferraretto: “As time of fermentation progresses, starch digestibility improves.” There is also about a 5 to 10 percentage unit gain in KPS.
Ferraretto noted that the current research suggests to not even feed corn silage until it has fermented 90 to 120 days in storage. He also mentioned that the development of new hybrids may shorten this recommendation in the future.
One final note on starch digestibility: Poor kernel processing at harvest cannot be compensated for by greater storage time. If it’s bad going in, it will be bad coming out. In other words, you have one shot to get it right.
Fiber manipulation
As with starch, research is also bringing to light new ways of improving fiber digestion in corn silage. Unlike conventional forage crops, corn for silage must be harvested based on whole-plant moisture. Harvest timing is not really an option to change fiber digestibility.
There are, however, two primary methods to improve fiber digestibility. One is hybrid selection with the most obvious (and maybe only) example being the selection of brown midrib (BMR) hybrids, which have significantly higher fiber digestibility than conventional hybrids.
This is where we come to the trade-offs. Brown midrib hybrids will typically have lower dry matter yields than the top tier of conventional hybrids. Further, many BMR hybrids will be lower in starch content and digestibility than conventional hybrids. Newer BMRs with a floury endosperm have been developed to help overcome this issue.
Another method to impact fiber digestibility is manipulating cutting height; this is a practice that is receiving more research attention and use in the field. The concept is simple — leave more lignin in the field.
Ferraretto and his graduate students recently completed a meta-analysis of cutting height research studies and developed simulation equations to predict the impact of high-cut corn on silage yield and quality.
In one of these simulations that was compared to an actual field study with good agreement, cutting corn at 24 inches versus 6 inches improved neutral detergent fiber digestibility (NDFD) by 3 percentage units, lowered NDF by 4 percentage units, and raised starch by 4 percentage units. At the same time, yield was lowered by about 10 percent, the same as might be expected by planting a BMR hybrid.
Ferraretto noted that perhaps the combination of greater plant densities and cutting height might lead to improved quality without compromising yields. Stay tuned. More research is on the way.
We’ve come a long way in improving corn silage. The savvy corn silage producer has learned that the benefits of new hybrid and machine engineering technologies can only be realized if silage production and storage strategies are top notch. Only in such situations can the combined milk-producing ability of both starch and fiber be fully exploited.