Compared to grain data, it is also more difficult to obtain meaningful side-by-side silage data given the complexity of weighing silage plots and then analyzing for nutritional traits. There are also considerable differences in how silage growers view the agronomics of silage hybrids compared to dairymen and nutritionists, whose ultimate goal is to turn silage into milk.

Starch
The current cost of grain has sensitized the dairy industry to the importance of starch in corn silage. As corn genetics improve, it is not surprising that silages are increasing in quantity of starch. This is important because starch accounts for more than 65 percent of the energy in corn silage. Furthermore, it takes a huge change in fiber digestibility to offset the energy associated with a very small increase in starch content.

Harvest maturity is a key driver of silage grain content. Advancing maturity results in increasing starch content by as much as .5 to .75 percentage units per day. Contrary to some older studies, it is becoming clear that neutral detergent fiber digestibility (NDFd) does not decline as much as once thought with increasing maturity as long as the plants are still healthy and actively photosynthesizing. In fact, in healthy plants, NDFd tends to remain fairly constant across a normal harvest window of one-third to three-fourths kernel milk line.

Some nutritionists have expressed concern about the hard-texture or vitreousness of corn kernels in silage. Silage growers should understand that when a seed company talks about “soft-texture” they are referring to the grain at dry grain maturity, not at corn silage maturity. And one can not assume a harder-textured hybrid at grain maturity will necessarily be a hard-textured hybrid at silage harvest maturity.

Research shows high test weight, (vitreous) grain does not have a negative effect on ruminal starch disappearance when fed as fermented feeds, such as corn silage or high-moisture corn (greater than 26 percent kernel moisture). The modifying effect of fermentation is often forgotten when people make statements about hard-texture corn. Dr. Jeff Firkins, from Ohio State University, recently summarized the current literature on starch digestibility and concluded that vitreousness of corn grain in silage seems to be of relatively little value. In contrast, vitreousness of dry corn grain should be considered to help users know when to grind corn more finely.

The use of kernel processors can have a huge impact on the variation in the rate and extent of corn silage starch digestion. To simply say silage was processed, is not enough. What is needed is information on the roller mill setting (e.g., typically 1 to 3 millimeter depending upon kernel maturity) and objective quantification of the extent of subsequent kernel damage using currently available laboratory tests.

The notion that corn silage can have too much grain conflicts with common guidelines for the amount of starch dairy cows can safely handle in the ration (typically 24 to 28 percent of the total ration DM). To put this in perspective, one can consider an extreme example of feeding 70 pounds of 30 percent DM corn silage containing 50 percent starch (highly unlikely, even with high-chop corn) consumed per cow per day. This would only contribute 10.5 pounds of daily starch intake. If cows are consuming only 50 pounds of dry matter intake, the total ration starch level from the corn silage in this extreme example would only be 21 percent starch. This is well within the acceptable guidelines of most nutritionists. By maximizing starch from corn silage, one can significantly reduce ration costs from supplemental starch without having to sacrifice reduced fiber digestibility.

Another flaw in the argument that silage can have too much grain is the claim that grain can always be added to corn silage and one should not sacrifice fiber digestibility to obtain high grain yields. Several university research studies have shown no relationship between grain content and stover digestibility.

Fiber
Despite marketing hype, there are very minimal “genetic” differences (2 to 3 percentage points) between commercial (non-brown mid-rib) hybrids for fiber digestibility.

Silage hybrids are no different than bulls. Their genetic transmitting ability must be evaluated independent of environmental influences. It is not valid to assume hybrid genetics as the primary cause of nutritional differences when comparing different hybrids grown in different fields. This is why seed companies and universities only compare similar maturity hybrids grown in the same location and planted reasonably close to each other (e.g., 10 to 12 rows apart, especially where soils are highly variable) in what agronomists called side-by-side, paired comparisons.

The large variation in fiber digestibility observed by nutritionists is more a function of planting population, growing environment, harvest maturity and fermentation efficiency. All you have to do to prove this to yourself is access any of the university silage plot research done in Wisconsin, Minnesota, Michigan or New York. What you will find is that very few hybrids, within the same plot, differ statistically from the plot average. This is because researchers are careful to compare hybrids of similar maturity. However, you will find significant differences among hybrids for tonnage and starch content.

Selecting a silage hybrid
Let plot data (e.g. agronomic traits, maturity, silage yield, starch content and fiber digestibility) help you decide which hybrids meet the specific agronomic and nutritional needs of your dairy. The importance of grain in silage is the basis for the fact that a “good silage hybrid” has to be a relatively “good grain hybrid,” but not all grain hybrids are suitable for silage because they may lack the plant height to meet our tonnage needs. Having 15 to 20 direct, side-by-side comparisons, over at least three growing seasons, is ideal. Demand high repeatability in your “silage proofs,” just like you do from “sire proofs.”

Conclusion
Here is a concluding management checklist to help growers and nutritionists manage and reduce corn silage variability:

1. Establish frequent communication between dairy feeding manager, nutritionist, growers, seed rep and chopper operator because the dairy has to live with the resulting corn silage for an entire feeding year.

2. Select hybrids with plot-proven (and similar) nutrient profiles focusing on yield and starch content which are highly influenced by hybrid genetics. Consider fiber digestibility of hybrids but understand that this is influenced primarily by growing conditions.

3. Minimize the number of hybrids to improve consistency (without compromising agronomic risk).

4. At harvest, focus on harvest timing, degree of kernel damage and bunker/pile compaction.

5. Consider segregating silage (by quality and/or milking string), just as you do with lots of hay.

6. Inoculate silage with a research-proven product to improve both feed value and feeding consistency (VFA profile, smell, taste).

7. Monitor kernel processing on the way into storage and quantify with lab test at feed-out; adjust silage and concentrate levels with the understanding that starch digestibility in corn silage can increase as much as 2 percent each month in storage.  PD

References omitted but are available upon request at editor@progressivedairy.com

Bill Mahanna
Pioneer Nutritional Science Manager
bill.mahanna@pioneer.com

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