Conversations: Ask your nutritionist about corn silage quality

Feed costs can represent as much as 60-65% of the total cost of dairy production. As producers and their advisors meet in the conference room (or kitchen), the conversation will turn to evaluating the quality of ration ingredients, especially corn silage.

By Jerry Weigel

Representing a growing share of the typical dairy ration, high-quality corn silage is vital for today’s high-producing dairy herds. But what does “high quality” mean? Here are a few questions to help decipher the results of your silage tests.

1) What are you looking for when you evaluate corn silage quality?

I look at representative (at feeding time) silage samples for moisture, fiber digestion, feed intake potential, crude protein (which could be a real economic variable) and any mycotoxin concerns. I also take into serious consideration the nature of the sample, how representative it is (I cannot emphasize that enough), as well as the lab that did the analysis. Finally, I consider what method was used to determine the quality.

Ask your nutritionist about sampling methods and what steps you can take to ensure representative samples are taken. When you receive your test results, ask your nutritionist to explain your corn silage moisture, fiber digestibility and crude protein levels, and how they fit in your feeding program. Find out if mycotoxins are a concern in your area.

2) What are important factors related to starch analysis?

I have to set a limit (approximately 30%) on the amount of available starch in the total dry matter of the diet. After I have the chemical analysis back, determined the net energy for lactation (NE-L) of the corn silage and found that we have good NE-L without excessive starch, it allows some additional ration flexibility with corn grain inclusions or the use of co-products. Additionally, I need to know the degree of silage fermentation – has the silage fermented for two months or four months?

Ask your nutritionist to explain starch evaluation, especially NE-L. Given the test results of your corn silage sample, is there ration flexibility for inclusion of corn grain or co-products? How does silage fermentation factor into starch analysis?

3) What about fiber?

We have to understand and, maybe more importantly, expect how the rumen will react to a given fiber, based on the forage source. As we learn more about the various fiber fractions and how the rumen reacts to these fractions, we can better predict how the forage will perform in the cow and even evaluate any synergies of ingredients within the diets.

Ask your nutritionist about corn silage fiber test results and how these results translate into rumen dynamics. Ask how corn silage fiber will interact with other ingredients in the diet.

4) How can an accurate assessment of my corn silage feed components reduce my total feed costs?

The historical average incorporation of corn silage into lactation rations on a percentage of dry matter has been around 45%, but recent evidence suggests that we could approach 60% with the right corn silage, one with a high-energy contribution. This is especially true when we have expensive corn prices, and we can increase the inclusion levels of corn silage in our TMRs. For example, if corn grain goes from $3.00/bushel to $4.00/bushel and we price silage at 10x per bushel of corn grain, we could reduce the corn grain in the TMR by 2 lbs./cow/day. In this scenario, the potential feed savings could be in the area of 4¢ per cow per day, just by eliminating 1-2 lbs. of corn consumption.

After evaluating the corn silage test results, ask your nutritionist about current corn silage inclusion rates. Given prices/values for other feedstuffs, could the inclusion rate be adjusted higher to reduce purchased corn costs? Why or why not?

5) What’s the best way to evaluate/predict corn silage digestibility?

Ask the cow! On a serious note, the total understanding of forage digestibility is critical to the economic returns of the dairy. Historically, we have only looked at acid detergent fiber (ADF), but recent information has now led us to believe ADF is a poor predictor of silage digestibility. It is my opinion as a nutritionist that there are three predictors for digestibility (neutral detergent fiber digestible, or NDFD): 1) Animal tests where the test ingredient is fed; 2) In vitro studies where the test ingredient is ground to 1 mm and dry matter disappearance is determined; and 3) In situ digestibility evaluation where the test ingredient is measured (as fed) in rumen fluid and fiber disappearance is measured. If one cannot use the cow, it is my opinion in situ is the best method, as this procedure comes the closest to what the rumen observes.

Ask your nutritionist to explain how predicted forage digestibility is determined, and what implications that has for your herd. Ask how herd performance can be expected to compare to predicted digestibility.


Jerry Weigel   is the manager of nutrition and technical service for BASF Plant Science. Contact him via phone at 919-547-2554 or e-mail:, or visit