Variation in Starch Content can Determine Corn Silage Quality

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Corn silage quality has typically been thought of as one of the more consistent forages produced on the farm. However, advances in forage testing have let us know that’s not really true.   

There can be a lot of variation in neutral detergent fiber (NDF) and starch content throughout the year, writes Virginia A. Ishler, Extension dairy specialist at Pennsylvania State University. Depending on the growing season and hybrid selection, the starch content can vary tremendously. Many farms do not include starch in their 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 or 48 hours) 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 2013/14 in monitoring corn silage quality over time (ensiled four to six weeks vs. six to seven months) have observed that one-third of the samples increased in starch digestibility. This is similar to the published research found in the Journal of Dairy Science. However, one-third of the farms showed no change and another one-third showed a decrease in starch digestibility. 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 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 three time points throughout the year, which include NDF, NDF digestibility (30 hours), starch and seven-hour starch digestibility. Record this key information, including the storage structure and hybrid.

Step 1. Send out samples after having fermented four to six weeks, six to seven months and nine to eleven months.

Step 2. Keep a record of dry matter percentage, 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.

Silage quality
NDF – 40.4% DM
NDFD, 30 hours – 50.6% NDF
Starch – 33.2% DM
7-hour starch digestibility – 81.9% starch
Silage quality 2
NDF – 31.1% DM
NDFD, 30 hours – 61.3% NDF
Starch – 43.4 % DM
7-hour starch digestibility – 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 will be feed costs for dry cows, springing heifers, pregnant heifers and growing heifers. The rations will reflect what has been fed to these animal groups at the Penn State dairy herd for the past six years. All market prices will be used. 

Standardized IOFC starting July 2014 

Income Over Feed Cost

Standardized feed cost/nonlactating animal/day starting July 2014

Standard Feed cost nonlactating

Virginia Ishler
Virginia A. Ishler, Extension Dairy Specialist, Penn State University

Headline image courtesy of Penn State University.


Original article by Virginia A. Ishler can be viewed here.

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