Defining Corn Silage Quality

Corn silage is considered a consistent forage throughout the year compared to the multiple cuttings of hay-crop forage. The main challenge affecting nutrient content can be the amount of rainfall during key development times and the impact on ear to stalk ratio.  With the advances in laboratory testing technology it is no longer just fiber and starch to consider, but their digestibility, the kernel processing score, and particle size distribution.  Based on all this added information, what defines good quality corn silage?

Production Perspective

The Extension dairy team at Penn State has been trying to bring more clarity to what defines corn silage quality. This is not a simple question and there is no clear-cut answer. Assuming the corn silage has an ideal fermentation profile and there are no problems with mycotoxins, what nutrient specifications should producers use to determine high or low quality silage? 

Fiber digestibility has been a key number many people refer to as they discuss the attributes of good quality corn silage. The assumption made is higher fiber digestibility produces more milk. This is not necessarily accurate based on an intensive field study conducted on twenty-four farms by the extension dairy team. During the first sampling period in 2016/2017 the corn silage NDFD 30-hr ranged from 48.6% to 69.7% of NDF.  The individual farms at the lowest and highest fiber digestibility averaged 93 and 78 pounds of milk respectively.  Both farms were feeding between 15 and 17 pounds of corn silage dry matter. For 2016 both farms had similar breakeven cost of production/cwt ($16.47 and $16.79) and feed costs/cwt ($7.86 and $8.14). Fiber digestibility alone does not determine how well cows will perform.

The level of starch and its’ digestibility is gaining more interest when evaluating corn silage quality. On the current project, the starch as a percent of dry matter ranged from 14% to 46% and the 7-hr starch digestibility ranged from 44.4 to 88.7 as a percent of starch. The two highest producing herds averaging over 90 pounds of milk both had their corn silage test 36% starch with a 7-hr starch digestibility of 80%.  The one farm fed 22 pounds of corn silage dry matter compared to 15 pounds on the other. Excluding the two highest producing herds, the range in milk production was 65 to 88 pounds. There was no pattern on starch level and digestibility as it related to level of milk production.

The kernel processing score may not technically be considered a quality parameter however it has been associated with higher milk production. In the current study, the two highest producing herds also had ideal processing scores but so did the lowest producing herd at 65 pounds of milk. The corn silage particle size distribution on the twenty-four farms did not provide any insights on animal performance but it did with storage structure. 

Ration information is collected at the time of corn silage sampling to evaluate the dry matter intake levels of corn silage, small grains, and hay crop forages. The ingredients used to supply energy and protein are captured as well. Currently there does not appear to be a specific strategy that is the silver bullet to achieving high milk production.

The ultimate result is how forage quality and nutrition affect the dairy producer’s bottom line. One single metric does not define corn silage quality. Based on our data to date, no one farm had the ideal forage quality for all metrics; meeting the industry standards for fiber and starch content along with their digestibilities and ideal kernel processing score and particle size.  This is not to minimize the need for good quality forage, but good management and nutrition can overcome some forage quality deficiencies. The other aspect is all these parameters can change over time when switching to a new storage structure and hybrid. The key is to keep track of what fields/hybrids are going into each structure, plan to sample routinely, and make the necessary ration adjustments to complement the forage quality.


Develop a plan for selecting corn hybrids that match the geographical location and manage hybrids in the various storage structures to monitor differences over time and the effect on herd performance. 


  • Step 1: Working with a nutritionist and crop consultant, discuss the needs of the cows and make decisions based on improving quality parameters of the silage in relation to fiber and starch digestibility.
  • Step 2: Record the fields and hybrids planted.
  • Step 3: Record the fields and hybrids going into the particular storage structures.
  • Step 4: Analyze corn silage for fiber and starch digestibility, kernel processing score, particle size distribution and fermentation profile.
  • Step 5: Monitor animal performance based on forage quality fed and discuss any changes with the nutritionist.
  • Step 6: Monitor income over feed cost and compare to the farm's breakeven number to check that income and expenses are in line for the level of milk production.

Economic perspective

Monitoring must include an economic component to determine if a management strategy is working or not. For the lactating cows income over feed costs is a good way to check that feed costs are in line for the level of milk production. Starting with July's milk price, income over feed costs was calculated using average intake and production for the last six years from the Penn State dairy herd. The ration contained 63% forage consisting of corn silage, haylage and hay. The concentrate portion included corn grain, candy meal, sugar, canola meal, roasted soybeans, Optigen (Alltech product) and a mineral vitamin mix. All market prices were used.

Also included are the feed costs for dry cows, springing heifers, pregnant heifers and growing heifers. The rations reflect what has been fed to these animal groups at the Penn State dairy herd. All market prices were used.

Income over feed cost using standardized rations and production data from the Penn State dairy herd.

Note: May's Penn State milk price: $17.36/cwt; feed cost/cow: $5.35; average milk production: 84 lbs.

Feed cost/non-lactating animal/day.