Poor Silage Warning in North Dakota

NORTH DAKOTA, US - Some producers are finding they have poor-quality corn silage this winter, according to a North Dakota State University dairy cattle expert.
calendar icon 16 December 2008
clock icon 4 minute read

“Properly ensiled, corn silage should have a light, pleasant smell with only a slight vinegar odor,” says NDSU Extension Service dairy specialist J.W. Schroeder. “It should be slightly brown to dark green. If it is dark brown or has an odor that is fruity, yeasty, burned or rancid, excessive heating or improper fermentation has occurred.”

Many crops in North Dakota were starved for heat units this past growing season and matured later than normal. As a result, these fields also were wetter than normal at harvest. So as the season progressed, some producers had little choice but to chop the corn for silage, resulting in improper moisture for ensiling and storage.

Excessively wet silage (greater than 70 percent moisture) usually results in fermentation dominated by undesirable butyric acid-forming bacteria, the loss of large volumes of highly digestible nutrients through seepage and poor animal performance due to low consumption.

For most crops, forage quality and value decrease with maturity; that is, fiber levels increase and digestible energy decreases. However, corn is somewhat unique in that quality increases with maturity. In corn silage, most of the digestible energy is in the grain portion.

Grain yields have been fairly good in many parts of the state this year, but despite waiting to harvest, the forage often was put up too wet for the silo, bunker or bag, Schroeder says.

Once plant cell respiration ceases, bacteria that feed on the available starches and simple sugars during the ensiling process produce acetic and lactic acids. For proper fermentation, silage storage requires air exclusion, temperatures between 80 and 100 degrees Fahrenheit and starches/sugars as food for the bacteria. Fermentation will continue until enough acid is produced to stop bacterial action. The desired degree of acidity, a pH of about 4.2, should occur within about three weeks after the silo is filled.

Three different kinds of silage may be found at different temperature levels during fermentation:

  • Underheated silage is drab green and has a strong odor; slimy, soft tissues; and a pH of 5 or higher.
  • Overheated silage ranges from brown to black and usually has a caramel odor of slightly burned sugar.
  • Properly heated silage is light green to yellow and has a vinegar-type odor, firm plant tissues and a pH below 4.5.

With too much moisture present, typically not the case in a more normal weather year, insufficient acid permits undesirable bacteria to produce butyric acid. These bacteria consume carbohydrates, protein and lactic acid as they multiply. Formation of butyric acid raises the pH and fermentation continues until all the readily available energy is exhausted. That is why a rancid-butter smell (butyric acid) indicates poor-quality silage that is low in energy.

“If you found yourself ensiling corn too wet this year, you can expect problems, such as frozen silage, seepage and a rancid odor,” Schroeder says. “These high butyric acid silages are associated with decreased dry-matter intake in dairy cattle and can be related to increased ketosis in herds since butyric acid is a precursor of one of the ketone bodies, beta-hydroxybutyrate. The net result will be slower gains in heifers, loss of milk production in lactating cows and a decrease in the corn silage you can use in any given diet.”

Mitigating the problem is not easy. Producers who suspect their corn silage is not up to par this feeding season should have it analyzed at one of the region’s forage testing laboratories or work with their feed company’s livestock nutritionist.

“This would be a good time to have your silage tested for organic acids,” Schroeder says.

Analyses commonly included in silage fermentation reports are for pH (alkalinity or acidity); lactic, acetic, propionic and butyric acids; ammonia; and ethanol.

Assuming that all nutrients are balanced properly in the diet, silage fermentation reports may be able to identify the reason for the cows’ intake or performance problems. If the goal is to see what type of fermentation process the silage went through, then collect a sample that is as fresh as possible and has not been exposed to air. Take samples at least 8 to 10 inches below the silage surface.

For chemical fermentation analyses, samples should be frozen immediately after being taken and then shipped, preferably on ice in a cooler, by a next-day delivery service. Ship at the beginning of the week so samples will not sit untested during the weekend.

Once you know the chemical analysis, you can adjust your diets to make up for some of the lost energy value with other feeds.

“Unfortunately, there is no quick fix,” Schroeder says. “While health-related issues are likely to be few, you simply won’t be able to feed as much silage per head per day without giving up some production.”

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