Testing Starch and 7-Hour Starch Digestibility on Corn Silages

8/17/2013 7:00 AM

I have received numerous phone calls and emails about low milk protein percents, high milk urea nitrogen and extremely low milk fat percents. Some of these problems occurred before the heat wave hit and others afterwards. What we are finding is that starch levels in the corn silage may not be as high as we assume and even though some of this silage has been stored for six or more months, the 7-hour starch digestibilities are low. This summer dairy herds are observing milk protein percents hovering around 2.75 to 2.85 percent. This is usually an indication of cows not getting enough energy in the way of starch and sugars. The herds I have been interacting with have milk urea nitrogens ranging between 13 to 15 milligrams per deciliter.

At Penn State we analyzed the BMR corn silage stored in an Ag Bag for 10 months. The starch tested 39 percent and the 7-hour starch digestibility was 68 percent. This compares to the conventional corn silage that had been stored in a bunk for eight months. It tested 42.5 percent starch with a 7-hour starch digestibility of 77 percent. The cows did not perform as well as expected on the BMR corn silage and the milk protein percent started to slip below 3.0 percent. When the TMR was analyzed, the ration starch was 20 percent instead of the formulated level of 24 percent. Everything else in the analysis checked out.

I assume that the starch level decreased in the silage as we were feeding it out. It may not hurt to be more diligent this summer with checking starch and its digestibility to make sure rations are what we think they are. Recommended ration starch levels can vary depending on many factors. I would expect corn silage 7-hour starch digestibility to be greater than 75 percent for material ensiled longer than six months. Milk urea nitrogens should range between 8 to 12 milligrams per deciliter.

For more information, contact the Penn State Extension Dairy Team. Call us toll-free at 888-373-7232, email dairyteam<\@>psu.edu or visit us at extension.psu.edu/dairy.

Editor’s Note: Virginia Ishler is the Penn State nutrient management specialist.

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