Livestock producers should take caution when changing animals from one source of silage to another. Too quick of a transition and quality differences can lead to unbalanced TMRs, acidosis, cows going off feed and potential health issues.

Ultimately, dairy cows could suffer a loss of milk production and potentially a drop in butterfat content. This is because new-crop silage can have higher or lower sugar, starch and NDFD levels than the old crop, plus different acids.

Chop length, processing and other factors may differ as well, notes Kevin Putnam, DuPont Pioneer dairy specialist.

Making a smooth transition
Animals need time to adapt to differences in feed sources, particularly from old-crop to new-crop silage. Experts suggest a gradual change. Feeding a mixture of old and new sources for several days can make the transition smoother.

“Rumen microbes require consistency. Abrupt changes between corn silage crops may result in rumen microbial upsets, depending on how much corn silage is in the ration,” Putnam explains.

“They need a minimum of seven to 10 days to adapt to new-crop silage. So transitioning feed over a 10-day period can help minimize some of the adaption problems.”

Sometimes the new-crop silage isn’t completely fermented, so essentially, green forage ends up in the ration and adds to rumen adaption problems.

To transition from last year’s corn silage to freshly ensiled or green corn forage, there are a couple of different options.

As stated earlier, a slow transition is the best, but if that isn’t an option, alter inclusion levels of forage sources in the ration.

If a high corn silage ration is fed, and alfalfa or grass forages are also in the diet, balance the ratios to at least 50-50 for as long as possible, considering alfalfa or grass-forage inventories.

Another option is buying fermented silage from a neighbor. And for a long-term proactive plan, a transition pile for next year or chopping an early hybrid about three weeks prior to when the silo will be filled, so there is feed at least three weeks fermented available, could be great options for avoiding having to feed green-chop.

Know what you’re feeding
“When transitioning into new-crop corn silage that has been fermented, feed characteristics need to be closely evaluated. Being aware of these differences between new-crop and old-crop silage can make for a smoother transition,” Putnam reports.

Several factors can impact the nutrient composition, or quality, of silages. Producers should consider environmental conditions for clues to silage quality, including a normal growing season versus a stressed-crop growing season.

For example, a year with dry conditions pre-silk will give you higher NDFD versus a year with adequate moisture and heat.

A year with adequate moisture and heat will usually result in a bigger plant and could result in lower starch levels due to the fiber portion diluting down the starch percentage.

Silage management practices provide another clue for determining nutrient availability.

Consider any operational changes to harvest maturity, harvest moisture levels, processing or packing, and covering practices from one year to the next. These may vary between old-crop and new-crop silage, making it important to understand the differences before making the transition.

“In the Northeast, I have been checking NDFD of standing corn to compare NDFD of 2012 corn silage to 2013 corn silage.

Due to most of the area experiencing adequate rainfall and heat this year in comparison to last year’s dry conditions, I expected NDFD to be lower. On average, I’m currently seeing 30-hour NDFD about four to five points lower than last year,” Putnam reports.

When analyzing and comparing differences between new-crop and old-crop silages, look for differences between the following:

• Starch, sugar and neutral-detergent fiber (NDF)

• Kernel processing

• Maturity of hay-crop silages

• Maturity of corn silage

• Length in storage

• Chop lengths

• Growing condition

• Dry matters

• Time in storage

Timing is everything

For many years, nutritionists have recommended that dairy producers wait until after Christmas to feed new-crop corn silage. Recently, researchers have brought to light a rational explanation for this decades-old recommendation.

It starts with the physiology of corn kernels and the changing rates of starch digestion. The starch granules are encased inside the kernel by zein proteins.

Over time in fermented storage, silage microbial activity and the chemical action of fermentation acids gradually solubilize zein proteins, freeing up starch granules for more rapid digestion by rumen microbes.

Another piece to this is the pericarp, or outer skin of the kernel – this is not digestible by rumen bacteria, making processing so important.

The more the kernel is processed, the more of the zein protein and starch matrix is exposed to the silage acids. This can lead to more starch digestibility at feedout.

As corn kernels in corn silage begin fermentation, they undergo their most rapid changes during the first two to three months in storage.

In animal trials in both the U.S. and Europe, it was proven that the rate of starch digestion changes rapidly over this period, providing scientific basis for the long-held recommendation to wait to feed new-crop silages.

Studies also indicate that corn silage starch digestibility plateaus after about five to six months in storage.

This finding is further supported by the monitoring of protein solubility and Amm-N in corn silage samples submitted to commercial laboratories; these samples indicate a rise in protein solubility and Amm-N concentrations caused by the solubilizing of the zein protein the longer the silage is in storage.

For the long term, these nutritional changes can cause problems of their own.

Part of the reason we tend to see higher milk production during the beginning months of the year is due to the corn silage having been ensiled for four months; starch digestibility has increased, other feed sources (haylage) are usually consistent, and the weather promotes less stress.

However, if starch levels aren’t adjusted for, these increases issues can occur when spring comes. The higher ruminal-available starch can lower rumen pH and issues can be magnified when summertime stresses occur.

This can lead to subacute rumen acidosis (SARA) and summertime heat stress, causing slug feeding, sorting, etc., and can lead them into full acidosis and milkfat depression.

By waiting to feed new-crop silage, growers avoid rapid changes in nutrition levels triggered by ensiling and maintain a more consistent feeding program. Determining when to feed new-crop silage is often influenced by inventory.

Fortunately, it appears that most rapid nutritional changes abate within the first two to three months of ensiling. Therefore, if feed inventories allow, it is best practice to wait at least two to three months after harvest before feeding new-crop silage.

In summary:

• Store forage in the silo at least two to three months before feeding.

• Producers and nutritionists should alter diet formulations when transitioning from old-crop to new-crop silages.

• Transition from old to new silage with a planned blending schedule where, for example, on day one, a minimal amount of new silage is fed, and by day 10, all new silage is fed.

• Continue to account for the upward drift in ruminal starch digestibility that occurs following the early dynamic period of ensiling.

• Monitor cow performance and health for signs of potential issues. PD

—From Dupont Pioneer

Kevin Putnam
Dairy Specialist
DuPont Pioneer