Corn silage harvest is complete for another year. As is often the case, silage inventory from last year’s harvest is running really low, and you are likely anxious to open a recently filled storage structure to start feeding it to your lactating cows. Not so fast! A proper plan needs to be in place to provide cows a smooth transition from last year’s corn silage to this year’s corn silage. Changing silage sources can have a dramatic impact on cow productivity and health.
Corn grain futures are currently running north of $6 per bushel for the fall months. Spot prices in some of the major dairy markets are still above $8 per bushel, when basis values are taken into account. Efficient utilization of starch in your dairy ration is important to your dairy’s profitability. Corn silage makes up a big portion of the forage in most U.S. dairy rations. Optimizing the starch digestibility in your corn silage can have a big effect on how much corn grain needs to be added to the rations for your lactating cows.
Once a silo or trench is filled with corn silage, packed and sealed, a lot of changes occur over the next couple of weeks and even months. The most obvious is that the temperature of the silage starts to rise as part of the normal fermentation process. Much of this is attributed to the microbial activity that initiates silage fermentation. Over a period of seven to 14 days, the temperature should eventually fall back toward ambient temperature, as the pH declines and lactic acid accumulation terminates the fermentation process. At this point, the fermentation should be about complete; however, nutrient (especially starch) availability will continue to improve over the next several months.
Ground corn is 65%-70% starch. Within the corn kernel, starch is encased in granules that are surrounded by zein protein. With freshly fermented silage, the zein proteins are intact and reduce the digestion rate of the starch. When the fermentation acids begin to accumulate in the silage, the chemical action of these acids gradually solubilize the zein proteins, exposing the starch and increasing the digestion rate in the rumen. The freeing up of the starch granules, while in the silo, is a gradual process. Over a period of three or four months, the rate of starch digestibility changes rather dramatically. This is often the basis for waiting to feed new crop corn silage, if possible. Research has shown that the starch digestibility of the corn in a silo usually plateaus once in storage for five or six months.
Consider variety differences
There are a number of factors that affect starch content and starch digestibility of corn silage. Weather during the growing season and grain maturity at harvest are known to influence the starch content of corn silage at harvest. Starch digestibility is also influenced by corn hybrid. Some of the newer hybrids claim to have higher levels of starch digestibility. Research has shown that the starch availability is improved in the newly ensiled corn hybrids for ethanol production, as compared to conventional varieties. If you chopped this corn hybrid for corn silage, you may want to consider opening that trench first as you start into 2022 silage. The improvements in starch digestibility will likely be advantageous when silage has been in storage less than three months. A complete nutrient analysis from your lab will provide your nutritionist with information on starch content and starch digestibility that is needed to adjust and balance your rations.
Corn silage moisture at harvest
Corn silage moisture at harvest is one of the many factors that influences starch digestibility. Field survey data collected over several years would suggest that when corn silage dry matter is greater than 36%, more starch ends up in the feces, suggesting lower starch digestibility. Dry matter content less than 32% can be problematic as well due to the lower starch content of the plant.
How long to wait
Fermentation may be complete in two weeks; however, you should ideally wait for three to four months before feeding new crop silage. This recommendation is based on the point where starch digestibility is nearing its peak. Higher starch digestibility means more energy for the rumen bugs. This translates into more metabolizable protein and metabolizable energy for the cow. Often, inventory of the prior silage crop is running low, dictating that the silo is opened well before three or four months post-ensiling. To avoid digestive upsets, do not include new silage in your rations until the fermentation process is complete, usually 10 to 14 days post-ensiling. Keep your nutritionist in the loop, as feeding this silage will require ration adjustments to minimize drops in milk production.
Opening the silo
Once the silo is open, it is essential that you take a good representative sample of the silage. When sampling a trench or pile, avoid sampling near the top and around the edges, as this is silage that likely was not packed well. Have the sample sent to a reputable analytical lab and request a full nutrient analysis. With new silage, it is usually a good idea to request a fermentation analysis, if it is not included in the package you have selected. When your nutritionist works the new silage into your ration, it is imperative that he or she knows how the nutrient analysis of the new silage compares to the silage that is currently being fed to the cow.
How fast to transition
Cows need time to adjust when going from old crop to new crop corn silage. Actually, it is the rumen microbes that need the time to adjust. Gradual changes are always the best. Ideally, the full change should take one to two weeks to avoid rumen microbial upsets. A good rule of thumb is starting with 75% old crop and 25% new crop. After five days, move to 50-50. Then on day 10, move to 25% old crop and 75% new crop. At day 14, move to 100% new crop. This may be more time-consuming for the feeder; however, it will minimize some of the adaptation problems and the potential loss of milk production that can occur when switching to new corn silage.
Which nutrients are most important
- Moisture percentage is of primary importance. The moisture content of the ration can tell us a lot about other nutritional characteristics of the silage, including starch digestibility.
- Starch percentage and seven-hour starch digestibility
- Neutral detergent fiber (NDF) and 30-hour NDF digestibility
- Linoleic acid is highly correlated to starch content. The higher the starch content, the higher the linoleic acid. A high level of linoleic acid in the ration is a known risk factor for milkfat depression.
Don’t overlook physical differences
Particle size of new crop corn silage and degree of kernel processing are two important characteristics that must be considered when transitioning to a new silo of corn silage. The Penn State particle size separator is a great tool to help you assess particle size distribution of corn silage. Most labs can run a kernel processing score (KPS). Degree of kernel processing can have a big effect on starch digestibility. A KPS under 50 suggests that the silage is under-processed; scores 50-70 are adequately processed. Scores over 70 indicate the silage has been optimally processed and will result in the highest starch digestibility, with minimal starch passing through to the feces.
Fecal starch
Fecal starch content is an analytical tool that can be used to estimate total tract starch digestibility. Research would suggest that fecal starch content is closely and linearly related to total tract starch digestibility, with an R-squared greater than 0.92. Most commercial labs now have the capability of testing for starch in fecal samples. Historical data would suggest that when fecal starch levels exceed 5%, there is likely excess starch escaping the digestive tract due to lower starch digestibility. Fecal starch analysis can be a cost-effective diagnostic tool to help determine the cause of milk production bottlenecks related to starch digestibility challenges.
Monitoring cow performance
Keeping good performance records is an important part of a smooth transition. Having a good history of0 dry matter intake, milk yield, milkfat percentage and milk protein percentage will help you gauge the impact when you transition to new corn silage. Having this information before and after the change will help your nutritionist make ration adjustments to optimize milk and component yield.
