Don't guess at nutrient value of corn silage

Don't guess at nutrient value of corn silage

Variable growing conditions call for precise analyses, not assumptions, of the 2012 corn silage crop.

*Dr. Elliot Block is senior manager, technology, for Arm & Hammer Animal Nutrition.

THE woes of the 2012 corn silage crop have been well documented and discussed, with some regions making it through the strange growing season relatively unscathed while crops in other areas suffered terribly.

Because the corn silage crop in some areas endured periods of drought while other areas began to experience drought conditions but then received rain, these variable conditions affected crop development and nutrient levels. Additionally, some silage may have low starch values, or it may have normal starch values.

In short, the crop is all over the board in terms of quality and composition.

This doesn't mean that dairies and their nutritional advisers feeding the crop are either safe or sorry depending on last season's growing conditions; it means that the challenging climatic conditions in 2012 probably had variable effects on the potential energy value of all components of the silage (starch as well as fiber).

The crops are in the silo, however, and must be fed to cows regardless of quality -- perceived and real.

 

Variability

Corn silage is grown as an "energy feed," with the energy arising from both the starch AND fiber in the corn plant. It is possible for starch values to be low while digestible fiber is adequate or above average.

It is also possible that although the corn crop "caught up" during the growing season, the starch or the fiber portion is not very fermentable. Corn that has not matured or had the kernels fill out may have highly available starch (lower prolamin).

However, cows are milking well on some of the drought-stricken corn. That's because under dry conditions, the plant does not make as much lignin or, more important, the linkages (ester/ether) to the hemicelluloses, resulting in higher digestibility than expected.

There are also examples in the Northeast and Upper Midwest where cows are milking well on corn silage that was put up at less than 35% dry matter and with lower rainfall but was harvested at the right time to get decent yields.

In other words, don't make too many assumptions about the nutrient value of the corn silage produced in 2012.

 

Mine the data

Rations can be formulated around all of the pitfalls IF the proper analytical methods on silage are used.

Obviously, if the analytical values are poorer than desired, the total diet cost will likely increase to make up the shortfalls. However, dairy nutritionists will still be optimizing income over feed cost for the individual farm's available corn silage.

The difficult and costly way to formulate rations given the variability in 2012 silage is to assume certain analytical values for the silage and "tweak the ration" regularly until the nutritionist feels that production performance has been optimized.

This may take months to accomplish, and the wrong assumptions can lead to health problems such as insufficient total dietary energy, subclinical acidosis, low milk fat and protein and all of the associated problems, e.g., poor reproduction, laminitis, anorexia, etc.

The easy way to accomplish sound ration formulation, especially when crop nutrient variability is suspected, is to use the modeling programs and laboratory analytical capabilities that are currently available.

This choice takes a bit more time initially, but it can and will get the cows to a better place in terms of productivity, health and economics much sooner and with less hassle than the "hunt-and-peck" method.

Follow these three steps for success:

1. Know which model your ration balancing platform uses. The major platforms use CNCPS 5.0 (CPM Dairy), CNCPS 6.1 (AMTS and NDS) or National Research Council (NRC) 2001. If other platforms are used, determine which model your platform most closely emulates.

2. Completely analyze forages for the components used in your nutritional model. Keep in mind that simply knowing the starch value is insufficient, particularly this year. It is just as important to get the correct value for the fermentability of that starch.

Corn silage neutral detergent fiber (NDF) values alone are not sufficient either. Use the values for rate and extent of NDF digestibility to get the diet closer to correctly predicting animal performance.

In this regard, NDF is not always NDF. The type of NDF analysis that is best suited for your ration formulation model will differ (more to follow). Every forage lab conducts the analyses requested and has different forms and formats for requesting the analytical procedures. Make certain to request the correct analyses for your ration formulation model.

In addition to the standard nutrient analyses, obtain results for these analyses:

* aNDF -- NDF done with the use of sodium sulfite, which solubilizes most, but not all, of the protein out of the NDF residue. It is used in the CNCPS 6.1 and NRC 2001 models.

* aNDIP -- This is the crude protein measured on the aNDF residue and is used in the CNCPS 6.1 and NRC 2001 models.

* NDR -- This is the NDF analysis performed without sodium sulfite and is used in the CNCPS 5.0/CPM model.

* NDRIP -- This is the protein done on the NDR residue and is used in the CNCPS 5.0/CPM model.

Determine which NDF digestibility assays will be most critical.

The models currently support the measurement of NDF digestibility at 24 and 30 hours.

Next year, the industry will move to a two-pool model, as suggested in the proceedings of the 2009 Cornell Nutrition Conference. This will mean 30-, 96- or 120-hour and 240-hour in vitro digestibility. The 240-hour uNDF will replace the need to do lignin testing and will better recognize the indigestible fiber, which is variable within as well as among plant species. This will allow nutritionists to better fine-tune rations for the amount of forage that can be fed -- but that is a concern for next year.

 

Starch fermentability

Ask for a seven-hour starch digestibility. This is a starting point and allows nutritionists to develop a Kd (rate of digestion).

Researchers are working with various forage labs to develop a more robust, multipoint measurement that will increase the robustness of the predicted single-pool Kd.

It is important that field nutritionists truly understand what to request in an analysis based on ration balancing tools used. For example, if CPM is used, ask for NDR and NDRIP. If CNCPS 6.1 is used, ask for aNDF and aNDIP.

Last, don't forget that stressed crops may contain more mycotoxins, and therefore, a mycotoxin analysis is essential when working with silage.

3. Enter the data obtained from the above into the nutrient profile of the feed. At this point, you can re-optimize the ration and come much closer to accurately knowing how the cow will perform and which ingredients may have to be changed.

Once the procedure is completed, it will be easy to see that it is not a difficult or daunting task. Further, by using these available tools, weeks or months of subpar performance or nutritionally induced health issues can be avoided because "typical values" for these parameters were not used.

Near-infrared (NIR) note of caution: Some of the forage analytical labs have robust equations to give reliable digestibility estimates by NIR analysis, but other labs do not. While NIR analysis will result in accurate estimates for major nutrients (except for minerals) in forages, if the forage you work with is not "mainstream," consider requesting wet chemistry to estimate digestibility and fermentability.

Volume:85 Issue:10

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