Corn Silage Variability

Jun 24, 2015
By Virginia Ishler
Extension Dairy Specialist
Production perspective:
The Extension Dairy Team has been working with approximately 60 farms evaluating corn silage quality over time. Samples are taken in the fall and again in the spring. Fiber and starch digestibility are being tested at both time points. Within farms it is amazing how much change is occurring in fiber and starch content and digestibility. As a nutritionist we tend to over-simplify things. For example, we focus on fiber digestibility as if that one parameter alone determines how well cows will perform. Unfortunately that does not match up with the reality on-farm. We are observing every combination imaginable related to fiber and starch measurements and the question becomes how do you deal with this nutritionally? 
The figure below shows the changes occurring in corn silage over time. If the forage is not tested routinely it is not surprising why cows may start performing better in the spring or in some situations why they are not milking as well as they did in the fall. When examining individual farms the extremes can be quite dramatic. For example, the starch digestibility (7-hr, % starch) on one farm went from 75.4 percent in the fall to 56.4 percent in the spring. This silage was resampled and tested twice with the same result. Another farm went from 60.7 percent in the fall to 78 percent in the spring (7-hr, % starch). Differences are being observed for fiber digestibility but appear less frequently and are not as extreme. 
Regular forage testing is recommended, especially for corn silage. The added expense of testing for both fiber and starch digestibility is warranted. 
Changes over time from fall 2014 to spring 2015 on nutrient parameters of corn silage.
 NDF, %DMStarch, %DMNDF digestibility 30 hr, % NDFStarch digestibility 7-hr, % Starch
Average-excludes outliers for NDF% (n=35)    
Outliers – major increase in NDF% (n=6)    
Outliers – major decrease in NDF% (n=7)    
Note: Data was sorted on 48 participating farms based on neutral detergent fiber changes from fall 2014 to spring 2015. This information is for illustration purposes only. Further analysis is being conducted to account for hybrids, storage structure and sampling time.
NDF=neutral detergent fiber
Action plan for sampling forages  
Goal – Develop a schedule for analyzing forages throughout the year. 
Step 1: Wait 5 days after opening a new structure to send forages for analyses.
Step 2: Sample corn silage in the fall and spring. Include fiber and starch digestibility.
Step 3. Sample hay crop forages when feeding a new cutting of alfalfa or grass.
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® 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 for the past 6 years. All market prices were used.
Standardized IOFC starting July 2014
IOFC May 2014
Note: May’s PSU milk price: $17.51/cwt; feed cost/cow: $6.55; average milk production: 84 lbs.
Standardized feed cost/non-lactating animal/day starting July 2014
Feed Costs May 2015
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