Forage testing’s 800-pound gorilla

By Mike Rankin

Most married folks learn over time it is often beneficial to avoid known topics of controversary, especially when they involve the other’s small quirks. Such a strategy just leads to a more happy and healthy life. In fact, “Don’t sweat the small stuff” is probably a good mantra even outside of a marriage.

But what if it’s big stuff? Those issues should be addressed, as painful as it might be.

Three sectors of the forage industry that have long been “hitched” are livestock producers, forage producers, and the forage testing laboratories. In a sense, each relies on the other for a profitable livelihood. Whether you feed forage or sell it, an accurate forage test is paramount to profitability.

The aforementioned 800-pound gorilla in the room has always been forage testing accuracy, and more specifically, why different results can be obtained from different labs. It qualifies as “big stuff” and has always been the source of a lot of angst.

Before getting too deep into this topic, let’s get a couple items on the table. First, forage testing has totally changed the industry and is at least partially responsible for the gains made in livestock production during the past 30 years.

Second, I don’t know of one person in the forage testing field . . . and I know a lot of them . . . who gets their kicks by sending people an incorrect forage test. Their livelihood is founded on accuracy. I do know there may be different opinions on how to achieve the most accurate test possible, just as there are differences of opinion on how to make milk, raise beef, or fertilize hay.

It’s also important to recognize that the largest source of error is in the sampling process, but we’ll leave that aspect alone for now. There are plenty of good reference materials that clearly define proper protocols for sampling hay and silage. Not following the correct protocols for obtaining a sample puts the burden of blame squarely on the sampler, not on the forage testing laboratory.

Most people are aware that there is a National Forage Testing Association (NFTA) that certifies labs each year based on procedures and forage test sample results. There is also a NIRS Forage and Feed Testing Consortium that supports labs in their ability to obtain accurate results from NIRS (near infrared reflectance spectroscopy) testing. Most forage labs (at least the reputable ones) participate in these quality control efforts.

Why do we get dissimilar results from different labs when the “same” sample is sent?

Let’s begin with the concept of “same sample.” How a same sample is defined becomes crucial to this discussion. A few years ago, I came up with this explanation of the various scenarios.

Same forage sampled twice: In this case, a hay lot or silage is sampled and bagged, and then the process is repeated, and a second set of samples is taken and bagged. These two samples are not the same, even if proper sampling procedures were followed in both cases. They are two samples from the same forage lot, but they are not the same sample.

Two subsamples are taken from the same parent sample: Here, the lot of hay or silage is sampled, and then two samples are taken from that larger original sample. The two subsamples are still not the same sample even though they both came from the same parent sample.

Same as previous, only the original sample is dumped and quartered: Though this might be a recommended technique to reduce the size of a large parent sample (especially for silages), grabbing two of the quarters and sending them off to different labs still doesn’t constitute the same sample. Both leaf and stem composition are likely different.

Send one sample to lab, and then they send whatever remaining unground forage material they don’t use to a different lab: Once again, not the same sample.

Send one sample to lab, entire sample is ground, mixed, and then split to forward one-half to a different lab: This is really the only accurate way to get “same” samples analyzed. Or about as close as you can get. It’s important to get the entire sample ground.

Most forage labs are more than willing to send the split, ground sample to another lab. In most cases, you won’t see errors beyond those inherent with lab technique precision, unless one lab is using significantly different lab procedures or NIRS equations than the other.

Other reasons

Even if you have the same dried, ground, and mixed sample analyzed by two different labs, results may still vary. For a metric like neutral detergent fiber digestibility (NDFD), labs will often differ because the in vitro wet chemistry procedure uses rumen fluid, and not all rumen contents are created equal. As such, the NIRS calculation for NDFD will likely show the same bias as a lab’s wet chemistry. This is a big problem in the industry and one that is currently being worked on.

Some measurements such as dry matter, crude protein, acid detergent fiber, neutral detergent fiber, and ash should not vary significantly between reputable labs. If they do, verification with wet chemistry is probably needed.

It can be frustrating when two forage testing labs return different forage quality results, especially if it means a lost sale. Though compared results will never be perfect, they should always be within an acceptable range of error assuming the same ground sample was analyzed by both labs.

Over the past years, here’s the approach I’ve always suggested when it comes to forage lab business relationships.

1. Find a lab you’re comfortable working with and that you know reports accurate, consistent results. Stick with that lab for your forage testing needs (sales or feeding) so that you can make valid forage quality comparisons over time on your own forage production.

2. If a buyer insists on a forage test from a different lab, only compare results from dried, ground samples. Have this done lab to lab. It’s the only way to make a same sample comparison. If the results are vastly different and you want to pursue a next step, wet chemistry remains an option.