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Digestibility: The key to unlocking forage quality, profitability

Kevin Jones Published on 18 April 2014

Since a dairy cow’s diet consists of from 40 to 60 percent forage, the quality of that forage has an enormous impact on the performance and profitability of the dairy. What exactly determines the quality of forage?

Forage quality is determined by the nutrient content and the digestibility of those nutrients. Protein, NDF, fat, sugar and starch are the nutrients to be most concerned with.



There have been many articles written and speeches given about how harvest timing affects forage quality. Earlier harvest for alfalfa and small grains lowers fiber and increases protein, fiber digestibility and energy. Corn is a little different in that harvest is timed to capture the best combination of starch content and fiber digestibility.

Most everyone knows that forages lower in NDF are considered higher quality. Because fat, fiber, carbohydrates, ash and protein must add up to 100 percent, lowering fiber (NDF) increases carbohydrates or protein or both, which increases the energy or protein of the forage.

But what a lot of people fail to realize is that increasing the digestibility of that forage can add the same or more energy along with keeping the benefits associated with fiber. Increasing 24-hour NDF digestibility from 48 percent to 55 percent in a ration with 55 pounds of corn silage allows for a 3-pound milk increase with no other changes.

The last two months of corn silage samples run through GHC Labs in Idaho show a range of from 35 to 75 percent in 24-hour NDF digestibility.

The question is: How can NDF digestibility be increased? There are several ways to accomplish this. Variety selection can have a big impact on digestibility. There are agronomic practices that will positively affect digestibility. Harvest techniques and silage inoculants can also be used to improve digestibility.


Variety selection is the first option to be used to maximize digestibility. There are huge differences in the NDF digestibility of different varieties. There is more information on corn varieties than on alfalfa or small grains, but there is some information available.

In addition to NDF digestibility, starch digestibility in corn silage is extremely important. Starch digestibility ranges from less than 50 percent to more than 80 percent for seven-hour starch digestibility. Choosing the varieties that will be the most digestible is the place to start.

There is not a lot of information on agronomic practices that can improve digestibility. But this is an area with a lot of potential for progress. The concept is not that different from getting high production and performance from a dairy herd. Anything that will improve plant health will help digestibility.

Stressed plants allow disease and molds to develop, which can lead to toxins in the forage. There are soil additives that help the plant take up more nutrients essential for growth that have shown a lot of promise.

Fungicide treatments at the four-leaf to five-leaf stage in corn have been proven to improve plant health and therefore digestibility. Fungicides on alfalfa have also shown improved leaf retention and therefore better quality. The fertility program, timing of application and the correct rates definitely affects plant health and productivity.

Harvest techniques and inoculants have been shown to play huge roles in the final digestibility of forages. Corn silage kernel processing can greatly impact the performance of a dairy herd. Corn silage processing scores are a valuable tool to evaluate the processing of the kernels at harvest.


Going from a score of less than 50 to more than 70 can have an impact of 4 to 5 pounds of milk on a high corn silage diet. A big issue with alfalfa hay, haylage and small-grain silage is added dirt. As much as 10 percent added dirt or ash can accumulate with poor harvesting techniques, lowering the feeding value significantly.

Inoculants can help digestibility. Our enzyme technology is improving all the time. Enzymes have been added to inoculants to break down the cell walls to provide added nutrients for the bacteria during fermentation.

An added benefit has been increased NDF digestibility. There are inoculants available that have shown the ability to increase NDF digestibility as much as 10 to 15 percent. It also looks like they will increase starch digestibility.

This information is all great as we plan for the upcoming crop year. But what can be done for forages being fed now that might not be as digestible as they need to be? Unfortunately, there are not too many options for improving forage already harvested. As mentioned earlier, enzyme technology shows a lot of promise.

But it is also very hit and miss. There are some labs around with fermentation systems that could be used to test different enzymes or enzyme cocktails on your forages. This is a good place to start and much less expensive than feeding a product to the whole herd.

Another option is to create your own digestible forage. A mixture of 50 percent ground corn and 50 percent soy hulls makes a corn silage replacement with 38 percent NDF and 37 percent starch. This is very close nutrient-wise to a good corn silage.

The difference is the amount of NDF that is fermented in the rumen is increased from 36 percent to more than 50 percent. This would allow for an additional pound of milk for every pound of dry matter replaced. If the diet contains enough effective fiber already, this is a very viable solution.

Starch and NDF make up more than 50 percent of most lactating diets. A change in digestibility one way or the other can significantly affect performance and profitability. While not associated with forge quality, it is important to mention that processing of corn grain is of equal importance.

Whether the dairy feeds ground corn, high-moisture corn or flaked corn, the processing can affect performance greatly. Not enough attention is devoted to evaluating fineness of grind or the flake weight of corn grain. Evaluating starch in the manure is a good place to start. Anything over 5 percent indicates too much starch escaping digestion.

With the current economic ratios in the dairy industry, high feed cost along with high milk prices, the digestibility of the nutrients fed can have an enormous impact on the bottom line. The tools to evaluate feeds and rations are fairly cheap and simple to use. Maximizing feed digestibility may have the most impact on profitability. PD

Kevin Jones is a dairy nutritionist and owner of Ghost Hollow Consulting with his wife, Tammy. The company provides nutritional consulting, feed testing, whole farm record analysis and employee training. He can be reached by email .