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Lab Reports

posted on September 1, 2016 /

“Lab Report Refresher” by: Mark Kirk

“Well its all Greek to me!” as our pastor reminded us Sunday this statement conveys the idea of the difficulty to interpret something written in a whole ‘nother language. Ever feel that way about a silage analysis from a forage lab? With all the abbreviations and numbers, what is it really telling us? Let’s sort it out.

Most feed tests are separated into 5 major categories: proteins, fiber, carbohydrates, minerals, and calculations. Within those categories there are several measurements and calculations and some times there is more than one number for a particular line analysis. Which ones should we be most concerned about?

One of the most critical parts to look at is the moisture. Ideal moisture for corn silage is 62-68% moisture. Any drier and the fiber and starch digestibility both suffer, any wetter and you lose the amount of starch as well as can run into fermentation problems.

In the area of proteins, CP or crude protein is one of the first things to consider. For corn silage the typical range is 7-9% and is reported as a percentage of dry matter. Since corn is a luxury feeder of nitrogen CP is strongly correlated to nitrogen uptake. Soluble protein will be between 40-60% of the crude protein. It will increase over time in fermentation. Solubility is related to higher starch digestibility as the indigestible prolamin proteins are broken down into a more useable form.

Fiber measurements are bit more convoluted especially because of all the abbreviations. ADF is acid detergent fiber, this is the mostly indigestible fiber portion with a common range from 20-30% DM. The lower the value the better. NDF is neutral detergent fiber. NDF is the potentially digestible fiber. Measurements are usually between 35-55% DM. Next would be NDFd or neutral detergent fiber digestibility. NDFd is the designation for how much of the NDF is digestible at certain time points. These time points range from 12-240 hours depending on the lab. Most common is 30 hr, good standard corn silage will be in the mid 50’s while BMR corn silage should be in the 60’s. Fairly new on the scene is uNDF, this is the undigesible portion of the NDF at certain time points. The lower the number the better, higher % of uNDF will cause lower dry matter intake.

The most energy dense portion of corn silage is starch. It is typically represented, as a % of DM. Corn silage that is greater than 35% starch is excellent. Percentage of starch is a good place to start but just like fiber we need to know how much of it available to the cow. The industry standard test is 7 hr starch digestibility. Any measurement over 70% starch digestibility is ideal. The newer the corn silage the lower the starch digestibility could be, digestibility will increase the loner corn silage is ensiled.

On most analysis there is a section for calculations. Total Digestible Nutrients, TDN range from 67-74% . Net Energy calculations are divided into several groups; lactation, maintenance, and gain. Milk Per Ton, MPT, is most common these days and is an estimation of you guessed it the approximate amount of milk a ton of corn silage will make. MPT over 3200 is good and anything over 3500 is excellent.

Feed analysis is an ever-evolving science. Most labs have great online helps as well as many university extension services. Helps like these can be just the tools needed to help you decipher the “Greek” in feed reports

    By Mark Kirk