When big rectangular bales are sold to dairies, the price is fair to both buyer and seller only if it accurately reflects the hay's feed value.

That's why it's important to use the right procedure when collecting samples for testing, say California and Idaho researchers. Big bales should be sampled differently from small ones, they say. But one basic sampling principle holds true, regardless of bale size:

"It's primarily a numbers game," says Dan Putnam, University of California extension forage specialist. "In general, the more cores you take, the better job of sampling you're going to do."

He and Steve Orloff, Siskiyou County farm advisor in Yreka, CA, have proposed new guidelines for big bale sampling. So has Ron Thaemert, Lincoln County extension agent in Shoshone, ID. The two sets of recommendations differ, but both call for collection of a large number of samples from several bales.

In 1999 trials, the California and Idaho researchers discovered big quality differences within and between big bales from the same fields. Their new sampling recommendations take different approaches to dealing with that variability. The Californians suggest sampling several locations across each bale end. Thaemert suggests taking a single diagonal sample per bale.

Both groups say more research is needed to determine which approach is best.

In California, ADF ranged from 29 to 41 in a seemingly uniform hay lot, Putnam reports. And it varied by as much as seven percentage points in core samples taken at different locations on the same end of the same bale.

In Thaemert's Idaho research, he measured crude protein differences of up to 3.5 percentage points within bales. Differences that great can lead to unfair pricing if sampling is inadequate, he says.

"We've had some real discrepancies in the pricing of hay. Is the producer getting a fair price from the dairyman or broker? Is the dairyman getting the right quality for the price he's paying? I want to make it fair for both the buyer and producer."

In the California study, supported by the Kern County and San Joaquin Valley Hay Growers Associations, Putnam, Orloff and graduate student Tracy Ackerly intensively sampled 10 one-ton (4 x 4') bales from the same field. Five were baled at 15% moisture, five at 8%. They cored each bale 48 times to a depth of 18". Sixteen cores were taken 1' apart in a grid across each end, then the bale was taken apart and 16 more samples were collected in the middle. Crude protein, ADF and NDF were determined for each core.

They found greater quality differences within bales than between bales. Quality measurements weren't significantly different in the middle of the bales compared with the ends, so they concluded that just sampling bale ends is sufficient.

Their preliminary recommendation is that big bale hay samples should be a composite of at least 20 core samples collected from various locations on the ends of several bales. Push the probe straight in to get a good cross section of stems and leaves, they advise.

"You need a lot of cores and you need to probe different positions on the face of that bale," says Orloff. "The standing recommendation for small bales is one core right through the center. That doesn't appear to be the case for the larger bales."

He and Putnam suggest using a probe that's no more than 18-24" long and 3/8-1/2" in diameter.

"With some coring devices you end up with too much material from an individual core," says Orloff. "That discourages you from taking 20-plus samples, because you end up with too large a sample."

Thaemert, however, isn't concerned about sample size. He uses a 36" probe because it's needed for the diagonal sampling procedure he recommends. He advocates one diagonal sample per bale, starting about 8" from the top or bottom of the bale end, and extending up or down at a 45 degree angle. Collect one sample from each of 10 bales in a 200-ton lot, he advises.

"You're going to have a fairly large sample when you're done," says Thaemert. "But if you do a good job of mixing that sample, you should get a very accurate reading of the quality of that lot."

"The problem with large samples is that they're difficult for labs to handle," Putnam responds. "Labs often subsample large samples, which defeats the purpose."

Thaemert compared diagonal sampling accuracy with straight-in samples collected from the top, middle and bottom of big bale ends. Diagonal sampling collected hay from a cross section of the other three locations.

"My results are showing me that the diagonal sample is the most accurate of the four," he says. "I'm getting a better sample, and it's closer to the average of the other three than any one of those three."

Thaemert adds: "I can't say this is the exact way you need to do it yet, but I believe pretty strongly that this could be a new method."