Corn Silage Quality

Virginia A. Ishler, Penn State Extension

Corn silage quality was typically considered one of the more consistent forages produced on a dairy farm.

Production perspective

Over the years with advances in forage testing that statement is no longer accurate. There can be a lot of variation in neutral detergent fiber (NDF) and starch content throughout the year. Depending on the growing season and hybrid selection the starch content can vary tremendously. There are many farms that do not include starch in the analyses, which can significantly affect how cows may respond to the formulated ration. In addition there is the digestibility of each of those nutrients. Most labs will test for NDF digestibility and offer differing hours (i.e. 24, 30, 48 hrs.) to closely mimic what is happening in the cow. Nutritionists tend to have their preference on the value they feel is most representative. Starch digestibility changes over the duration of storage. Data summarized by the Extension Dairy Team from 2013-2014 in monitoring corn silage quality over time (ensiled 4 to 6 weeks vs. 6 to 7 months) have observed that a third of the samples increased in starch digestibility. This is similar to the published research found in the Journal of Dairy Science. However, a third of the farms showed no change and another third showed a decrease in starch digestibility. This project is being repeated in 2014-2015 to evaluate if the same trend occurs. The bottom line is that knowing your forage quality is just as important as knowing your cows. Neither cows nor forages are a static entity. Both are dynamic and as such need a monitoring plan to help maintain consistency and precision feeding.

Action plan for monitoring corn silage quality

Goal – Using wet chemistry and the same lab, test corn silage at 3 time points throughout the year, which include neutral detergent fiber (NDF), NDF digestibility (30 hr.), starch, and 7-hr starch digestibility. Record this key information including the storage structure and hybrid.

Step 1. Send out samples after having fermented: 4 -6 weeks, 6-7 months and 9-11 months.

Step 2. Keep a record of dry matter percent, NDF, NDFD, starch, starch digestibility, storage structure, and hybrid.

Step 3. Make notes related to ration changes, milk production and components associated with the corn silage analysis.

Step 4. Discuss corn silage quality and animal performance as necessary with the advisory team or appropriate consultants.

NDF – 40.4 % DM
NDFD, 30 hr – 50.6% NDF

Starch – 33.2%DM
7-hr starch dig – 81.9% starch

NDF – 31.1 % DM
NDFD, 30 hr – 61.3% NDF

Starch – 43.4 %DM
7-hr starch dig – 68.2% starch

Economic perspective:

Monitoring an economic component is necessary 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 will be calculated using average intakes and production for the last six years from the Penn State dairy herd. The ration will contain 63% forage consisting of corn silage, haylage and hay. The concentrate portion will include corn grain, candy meal, sugar, canola meal, roasted soybeans, Optigen and a mineral vitamin mix. All market prices will be 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 for the past 6 years. All market prices will be used.

Standardized IOFC starting July 2014

Note: November’s Penn State milk price: $24.06/cwt; feed cost/cow: $6.33; average milk production: 83.0 lbs.

Standardized feed cost/non-lactating animal/day starting July 2014


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