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Nutrition by Dr. Jim White
Silage low or high? Depends on the goal
For a number of years there have been projects to address the nutritional shortcomings of corn silage. The projects have usually targeted either protein or energy content. Protein studies have looked at either increasing the amount of protein, improving the quality of protein or doing a better job of preserving the existing protein. The studies concerned with energy content usually look at starch content, plant maturity, fiber digestibility or fiber content.
Often corn silage is a significant part of the ration dry matter. Midwest backgrounders routinely feed corn silage with 10 to 25 percent added grain and supplement to maintain 2 to 2.5 pound average daily gain. Midwest dairy producers will run corn silage as 10 to 50 percent of the dry matter for milking cows. I have fed as high as 75 percent of the dry matter as corn silage, but such a level is more common for the northeastern United States or for the French. At high levels of feeding, corn silage needs to be a source of effective fiber. At the lower levels typically fed in the Midwest, corn silage is looked on as an energy source. If the corn supply is cheap and abundant (days that seem to be in the distant past), then the corn silage fraction most likely to be of greatest interest is the fiber, particularly fiber digestibility. To improve fiber digestibility, there has been some work in selecting corn for lower lignin content, lower fiber content, higher fiber digestibility, the brown mid-rib trait, lignin to fiber ratio, etc. Another approach has been to raise the chopper head and cut the corn just below the ear, leaving the lower part of the stalk in the field.
It is not a bad idea. But before we all dash out and check the hydraulic fluid, perhaps we should consider what the differences are between normal cutting height and high-cut corn silage. The table below is a compilation of Midwest trials comparing corn silage cut at different heights.
With high-cut silage, the dry matter, starch and digestibility increase while the fiber content and yield decreases. This is as you would expect—the ear is usually drier than the leaves or the stalk. The lower internodes are more fibrous and less digestible than the upper internodes. Of course, leaving material in the field will reduce yield.
Other things to consider when thinking about using high-cut corn silage in milking rations:
1) The net gain is minimal for feeding high-cut corn silage. When substituting normal cut silage pound for pound, increased milk is somewhat offset by reduced fat test.
2) When feeding to a NDF specification, say 30 percent NDF, you will use up to 6 percent less grain in the rations.
3) Feeding high-cut corn silage to similar NDF levels has resulted in similar milk production, milk fat and feed intake. Depending on how silages are priced, rations costs will not change or see a 15-cents-per-cow-per-day swing up or down.
4) Lower grain feeding in high-cut corn silage rations is offset by the lower silage yield.
5) Comparing normal cut to the high-cut, the high-cut corn silage will usually calculate as having higher milk per ton of silage, but lower milk per acre harvested.
6) High cut corn silage would be most beneficial when fed to high producing herds, where milk fat can be maintained, i.e. high-forage diets.
7) Agronomic reasons may favor high-cut corn silage, i.e. soil cover or organic matter.
8) High-cut corn silage can be a tool for altering the moisture of the silage, i.e. the custom chopper shows up a week early, but can’t be back for 3 weeks.
9) High-cut corn silage may be more favorable if grain prices are high.
10) High-cut corn silage may be favored if storage capacity is limited.
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