Corn silage viewed as cropping option

Producing corn silage for dairy rations could be a good fit for some Southeastern cropping systems, says John Bernard, University of Georgia animal and dairy scientist.

“There are opportunities for producing corn silage for yourself, and also for producing for dairies in the Southeast that need additional forage beyond what they can provide,” Bernard told a group of farmers at the recent Sunbelt Expo Field Day in Moultrie, Ga.

Corn silage, he says, is the primary forage used in dairy rations in the Southeast. “As we look at some of our beef operations, corn silage also fits in nicely as a supplement to pasture during the winter.”

Many things must go into the making of a good crop of corn silage, notes Bernard. “It starts with the selection of a good corn variety. Then, we must focus on maintaining the quality of the crop, and this includes more than just high yields.

“Whenever you feed a crop, it must be very digestible. It has to be something the animal can use to convert to milk or meat. If the crop doesn't convert very well, then you won't be successful,” he says.

Corn grain represents approximately 50 percent of the total dry matter (TDM) in typical corn silage, so how farmers manage the crop is different from other forages, says Bernard.

“Although corn is more forgiving than other forages in terms of quality, other factors are necessary to maintain quality, including stage of maturity at harvest, proper storage and silo management,” he says.

As corn matures, the fiber content decreases while the starch content increases, he continues. “The decrease in fiber concentrations is a dilution effect related to the increase in grain content. Fiber digestibility decreases as the corn plant matures, similar to that of other forages. This is due to increased lignin concentrations.

“Starch digestibility decreases after the grain reaches the two-third milkline because of the hardening of the kernel.”

Under normal circumstances, adds Bernard, dry matter intake is not affected by the state of maturity that corn was harvested, but milk yield is affected.

“Milk yield increases as corn matures from early dent to the two-thirds milkline and then declines. The decline is due to the lower energy value related to the lower digestibility of starch and fiber in corn harvested after the two-third milkline.”

Based on normal changes in nutrient content and apparent digestibility, it's recommended that corn be harvested for silage beginning at one-half milkline so that harvest can be completed by two-thirds milkline, says Bernard. The stage of maturity can change from one-half to two-thirds milkline very quickly in the hot, humid conditions of the Southeast, he adds.

Hiring a custom harvester has become a common practice because harvest timing is so critical, he says, and because most producers don't have the machinery to harvest their crop in a timely fashion.

“Corn that has reached two-thirds milkline or black layer can be mechanically processed during harvest to improve digestibility. Processing can be achieved by using a kernel processor on the silage chopper.

“These processors have two counter-rotating rolls with one roller running at a faster speed than the other. This crushes or shears the kernel, cob and stalk, thereby increasing starch digestibility. But it also may decrease the effectiveness of the fiber in the silage.”

Kernel processing increases the digestible energy content of corn silage at all stages of harvest, says Bernard, but the largest increase is realized when corn is at two-thirds milkline or black layer.

“Kernel processing typically isn't recommended for corn that has not reached two-thirds milkline because of reduced fiber effectiveness coupled with lower increases in nutrient digestibility and animal performance.”

One observation dairy producers make when feeding kernel-processed corn is that there is less corn in the mature forage, he says. Also, fewer cobs will be visible in the feed bunk because of reduced sorting.

“It has been suggested that kernel processors should be set no wider than four millimeters for corn at two-thirds milkline or black layer, but there is limited research to provide exact guidelines, he says.

Corn harvested for silage, says Bernard, should be treated with an inoculant that has sound research data. “Ideally, the inoculant would be applied in the chopper to provide good distribution in the silage. When this isn't possible, it's important to get the inoculant mixed into the silage as thoroughly as possible.

“It's important to store inoculant properly and apply them according to the manufacturer's directions. Inoculants drop the pH of the silage by increasing lactic acid production. This reduces the time until fermentation stabilizes. Many research trials have shown that inoculated silage is more stable during feed-out.”

Once corn has been chopped, he says, it's essential to get it packed tightly in the silo to exclude air. “This is one of the most important jobs associated with making good silage. Poor packing results in prolonged respiration burning up digestible nutrients. The packing tractor should be the first piece of equipment to start running and the last to quit each day.”

Once the silo has been filled and tightly packed, it should be covered to exclude air and rain, adds Bernard. “Nutrient losses in the top three feet of bunker silos are 16 to 37 percent greater for uncovered silos compared with covered silos. The nutrients lost are those that are most digestible, so the reduction in feed value is greater.

“Depending on the size of the silo, this can represent a loss of several thousand dollars in the value of the silage.”

When the silo is opened, it's important to manage the face of the silo to minimize secondary fermentation losses, he says. Ideally, six inches of silage should be removed from the entire face of the silo each day to keep the silage fresh.

“If the silo is too wide to achieve this, silage should be removed from one-half of the silo for several days or weeks. Care also should be taken to keep the face of the silo firm. Dry matter losses may double or triple when the face of the silo is loosened and feed-out is extended from one day to two or three.”

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