Many dairy farmers are now paying more attention to the newer analytical parameters describing corn silage, especially neutral detergent fibre (NDF), which is needed in diets to help maximize milk yield, efficiency of feed utilization and animal health.

NDF digestibility (NDFd) is a parameter of NDF that measures the digestibility of the fibre in the corn stem, leaves and other nongrain portions of the whole- plant corn silage and is important for predicting:

• The quantity of corn silage the cow will consume before getting full
  
  
• Potential milk yield by feeding the corn silage

NDFd is analyzed at different rates – 24-hour, 30-hour and 48-hour – to estimate the amount of NDF that would potentially be digested prior to passing from the rumen.

The goal of these results is to help estimate the rumen retention of forage, gut fill and how much volatile fatty acids (VFA) will be produced, which in turn, estimate energy metabolism and milk production. NDF has the greatest nutrient yield and is most digestible over a 30-hour period, expressed as a percent of the total NDF (NDFd 30-hour).

NDFd 30-hour ranges for corn silage

The typical range for NDFd 30-hour for conventional (non-brown midrib) corn silages lies between 46 percent and 60 percent, with an average of around 55 percent. Conventional corn silages with NDFd 30-hour values in the high 40s or low 50s result in lower intake levels and reduced milk production potential.

So what steps can the farm team, nutritionist and feed advisers take to improve this? While there may be some minor differences between conventional corn hybrids in field trials, two of the major and overriding factors influencing NDFd 30-hour results are:

• Weather patterns during the growing season
  
  
• Cutting or chopping height

It’s a given that weather is one variable that cannot be controlled. However, cutting or chopping height can be adjusted and merits consideration as a step in improving NDFd 30-hour.

The lowest portion of the conventional corn silage plant is much less digestible than the rest of the stalk, and, in some growing seasons, may be higher in nitrates. One must ask, how much of that indigestible stalk do we really want to feed? It might add to total yield, but the lower stalk adds no nutritive value to high-performing dairy cow rations.

Yield versus nutritional content

The cutting or chopping height for corn silage should be reviewed annually according to operation size, total forage stocks and overall corn silage inventory. The first priority to be considered is to not run short of ensiled forages, including corn silage. After that, there is good independent research showing the benefits and trade-offs between typical and high-cut conventional corn silage hybrids.

For example, raising the cutting height from 15 centimeters (6 inches) to 30 centimeters (12 inches) will reduce total yield by 3.6 percent. Similarly, going from 30 centimeters (12 inches) to 45 centimeters (18 inches) further reduces total yield by another 3.6 percent.

However, increasing cutting height also increases the finished corn silage quality. A review of 11 published papers on this subject by Pennsylvania State University showed significant increases in nutritional value in the high-cut versus the low-cut conventional corn silage (Table 1).

High-cut conventional corn silage had a higher dry matter content overall, as the proportionally higher grain fraction is drier than the stem. With high-cut corn silage, it is important to note that harvest will occur three to five days earlier to achieve the target dry matter in the final corn silage. Also, with a higher proportion of grain, the starch content will also be higher in the resulting silage.

Proper kernel processing still applies to get the maximum value from the kernel starch. With less stalk harvested, the NDF content is lower in the high-cut corn silage, and as expected, the NDFd 30-hour is higher.

Cow performance

There have only been a few studies that followed the milk yield performance of high-cut and low-cut corn silage in lactating dairy cows. In some of the studies, the higher NDFd 30-hour corn silage was used to allow additional corn silage inclusion rates and lower grain energy inclusion rates, with a net ration cost savings.

Other studies that did not increase forage inclusion rates, found higher average daily milk yield per cow (+1.5 kilograms), but noted it was a challenge to maintain butterfat yield. It is likely the negative effect on butterfat yield observed in these controlled research trials could have been avoided with a more commercial or real-world diet formulation approach, but it is a potential risk that should be considered.

Implementation

It is important producers have a discussion with their nutritionists and feed advisers about forage stocks, corn silage inventory, storage facilities, corn silage quality over the past few years and current corn silage harvesting practices. Is a high-cut conventional corn silage right for you as a way to increase corn silage quality? What are your goals and drivers – maximize yield or high-quality corn silage?

Things to remember:

• This only pertains to conventional corn silage hybrids
  
  
• High-cut corn silage will have lower yields per acre
  
  
• High-cut corn silage can be cut and/or chopped a few days sooner
  
  
• High-cut corn silage has a higher nutritive value than low-cut corn silage
  
  
• The best economic return for high-cut corn silage is to use it in high-yielding dairy cow rations
  
  
• High-cut corn silage allows for higher inclusion rates, with savings in grain energy inputs
  
  
• Feeding high-cut corn silage can increase milk yield per cow, but attention in diet formulation will be needed to maintain and promote butterfat yield

High-cut corn silage is another tool an operation can implement to manage nutritive value, overall ration costs and harvest timing of corn silage. However, there are several operation-specific factors that should be considered before this decision and implementation are made, as well as ration balancing and monitoring after a change is made.

It is important for producers to do their own analyses alongside their nutritionist and feed advisers to ensure a successful transition to high-cut conventional corn silage.  

References omitted but are available upon request. Click here to email an editor.

• Tony Hall

• Dairy Technical Service Manager
• Lallemand Animal Nutrition, North America
• Email Tony Hall

Silage management rules still apply when working with high-cut corn silage

• Ensure the kernel processor setting is no wider than 2 millimeters at harvest to ensure an excellent processing score
  
  
• Discuss the optimal theoretical length of chop (TLC) with your nutritionist. For many, the TLC will range between 14 to 20 millimeters, but that can depend on dry matter at chopping, packing density opportunity and method of storage (tower, bag, bunker or pile)
  
  
• Always use a research- and field-proven silage inoculant to promote both an efficient front-end fermentation along with aerobic stability during feedout
  
  
• Ensure proper pack density is achieved by measuring tons harvested per hour along with tractor numbers and weight