“We get feedback from producers and even nutritionists, at times, that all corn silages are pretty much the same – they’re low-protein, high-energy forages,” said Karl Nestor.

“That’s not true anymore,” said the senior animal nutritionist at Mycogen Seeds during the California Alfalfa and Forage Symposium in Visalia last month.

Plant breeders have worked the past 20 years to design silage corns with different nutrient contents, he added. “Hopefully the biggest take-home point from this talk today is that you should take a deeper look at corn silage.”

Judge corn silage on its starch and fiber digestibility rather than just on yield, he said.

“Starch itself is very digestible by the dairy cow; the trouble is getting to it.” Once the protective covering, or pericarp, on corn grain is broken through processing, starch becomes “readily available. So saying starch digestibility sometimes may not be correct. In a way, we might be talking more starch availability.”

Forage dry matter, particle size and endosperm type all affect just how much starch becomes available to a dairy cow.

The pericarp on corn grain softens with higher moisture, allowing better starch digestibility. More mature plants with increased dry matter can reduce starch digestibility and milk production, according to studies. Starch becomes more available when stored at least seven or eight months, recent research shows. “Sometimes you run into a potential acidosis problem in dairy cows and, without much change in the ration, what has simply occurred is that starch has become more available in that stored forage.”

Kernel processing also increases starch availability. “Processing has allowed us to maybe get to some of those digestible starches when we couldn’t before.”

Producers should be aware of two endosperm types in silages: flinty, vitreous and floury, non-vitreous. The more vitreous or hard the endosperm is, the lower the overall starch digestibility.

“One reason why grain hybrids can make somewhat poor choices for silages is that they can contain a lot of vitreous- or flinty-type endosperm,”
Nestor said.

Fiber digestibility, measured as neutral detergent fiber (NDF) digestibility, now can range from 30% to 75%. As NDF digestibility increases, it boosts dry matter intake and increases in milk production, Michigan State University research shows.

“The relationship they reported was that, for every percentage increase in NDF digestibility, milk production is increased 0.55 lb per cow per day. This indicates that NDF digestibility should be a key consideration in your forage selections, as it can directly affect the performance of your dairy cows,” Nestor said.

If choosing a hybrid based on NDF digestibility, pick one that’s at least four or five percentage units different from your reference hybrid, he advised the group. “Differences smaller than this may not be statistically different and may be due to lab variation.”

Brown midrib hybrids can have up to 12 percentage units of increased NDF digestibility over typical corn silages, he added.

Most commercial labs measure NDF digestibility using in vitro or near-infrared reflectance (NIR). In vitro is more costly and gives a better measurement than does NIR, so it can help when deciding between two hybrids. NIR is valuable in ranking hybrids by NDF digestibility.

Be sure to choose one incubation time – a 48-hour, 30-hour, 24- or even a 12-hour in vitro test –and stick with it. That allows you to accurately compare hybrids. Having all tests done at the same lab will also keep comparisons consistent. For more on testing NDF digestibility, see “NDFD Numbers Helpful When Used Correctly.”