Let’s say you took several cores from one large square bale and several more from the next one. Then you had the two samples analyzed the same way at the same forage lab. Would their forage quality be about the same?
Maybe. But most likely not, according a recent National Forage Testing Association (NFTA) hay-sampling demonstration.
Even the quality within one of those bales could be highly variable from one spot to the next, says Kevin Grooms, an NFTA board member and laboratory director with Olsen’s Agricultural Lab, McCook, NE.
He was part of a study in which NFTA board members probed large square, large round and small square bales during an annual meeting to check hay-quality variability.
Six groups of people, including forage-lab personnel and members of the National Hay Association and American Forage & Grassland Council, were trained to take samples. Bales were divided into six sections, each of which was sampled by someone in each of the six groups.
“Essentially, we were getting six cores out of one-sixth of each bale,” Grooms says. Samples were then analyzed and the results studied.
“Everyone was very surprised. We knew that there was going to be variability between bales as well as within a bale, but we didn’t predict that it was going to be so great.”
For instance, the relative feed value (RFV) among samples from two 3 x 4’ large square bales varied as much as 58 points. Crude protein (CP) varied by 3.61 percentage points. One of those bales averaged 181 RFV points and 22.7% CP. But RFV varied within that bale by 44 points and CP by 2.35 percentage points. The other bale’s samples averaged an RFV of 154 points and a CP of 21.04%. RFV results varied within the bale by 27 points; CP by 1.62 percentage points.
RFV varied by 33 points and CP by 2.3 percentage points among samples from two 3 x 3’ large square bales tested. Within the two bales, RFV varied by 27 and 16 points, and CP ranged around 1.6 and 0.76 percentage points, respectively.
Samples compared from two large round bales showed a variability range of 44 RFV points and 3.44 CP percentage points. RFV averaged 123 for one bale with a range of 35 points among samples within the bale. CP for that bale averaged 15.9% with a range of 3.55 percentage points. The second bale averaged 130 RFV showing a range of 27 points. Its CP averaged 15.54%, but samples within that bale varied by 3.12 percentage points.
Small square bales were also sampled, but not in the same procedure as the large bales, Grooms says.
The demonstration showed “that variability exists within any given bale of hay or forage,” he says, and that “multiple samples must be taken to average out the variability of a lot of hay. The sampling points should be consistent throughout the lot. And bales to be sampled in a lot must be selected randomly to better represent the overall lot.
“In one lot of hay, you should core at least 20 bales, compositing them into one sample bag,” he says. Don’t split or sub-sample unground samples – doing so will create two potentially different samples.
If a ground split can’t be obtained, Grooms advises sellers and buyers to take samples from the same spot in a bale. “We know of hay producers who send bales overseas. They will sample in a certain area of a bale and then will put a marker in it. That way, the buyer can sample the bale right next to where the grower sampled it.”
The more cores taken, the better representation from a hay lot, he says. Sometimes one-core samples are submitted to his lab that are supposed to represent entire hay lots. On the flip side, he may get a box of freshly cut alfalfa taken from a windrow that’s also not representative.
The demonstration taught board members another lesson, says Tom Keene, the University of Kentucky hay marketing specialist who showed them how to take samples.
“It’s pretty hard work if you do it right – climbing over bales and trying to get probes in the right angles and the right ends of bales. I think it gave them much better insight into collecting a sample,” he points out.
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