July 15, 2004

Accuracy of Forage Sample, It’s in Your Hands

By J.W. Schroeder, NDSU Extension dairy specialist

Knowing the quality of forage is paramount to pricing, whether you are buying or selling. Hay sampling is probably the most important aspect of forage quality testing. Accuracy is in the hands of the sampler.

When you think about it, we expect a lot from very little. A pinkie-sized ground-up sample weighing less than a gram must represent tons of hay from a variety of fields. Once in the lab, this gram is sub-sampled from about a half-pound of material provided by the sampler, so it is critical that the sample given to the lab accurately represents the hay being tested. Whether the sample accurately represents a stack is the responsibility of the sampler. The lab can only test the sample presented to them!

Weather damage and delayed harvest has had a significant effect on hay, especially alfalfa. The proportion of protein and fiber of leaves and stems are very different and influenced by harvest stage and conditions. To determine nutrient quantity and quality, the sample of forage must represent the leaf to stem ratio of the bales, as well as the weed composition of the hay. Both can vary considerably across and between fields. Aside from supply and demand issues, accurate analysis of forage can be the single greatest determinant of price. Following proper protocols will help the sampler obtain a fair, representative sample of the hay lot.

When these sampling protocols are followed closely, different samplers can usually repeat the lab measurements within a reasonable range. These protocols are fairly universal, but they do vary slightly from region to region. Here are some important steps and guidelines for taking alfalfa hay samples:

• Identify a single lot of hay – Lots must be from the same cutting, variety and field. They also must be at the same stage of maturity and harvested within 48 hours of each other. Do not mix lots. A lot must not exceed 150 to 200 tons. If you know of differences in quality, separate into different lots.
• Choose a good, sharp coring device - The coring device should have an inside diameter on the cutting edge of at least 3/8 inch and no more than 5/8 inch. The cutting edge should be at right angles to the shaft and kept sharp. Dull probes will cause material to be pushed out of the core. Do not use an open auger or corkscrew type device which selectively samples leaf or stem parts.
• Sample at random - Walk around the entire stack and sample bales at various heights to the best of your ability. Do not avoid some bales or choose others; sample at random. Try to obtain cores from as broad a group of bales as possible within the stack.
• Take enough cores - Per lot, sample a minimum of 20 bales (one core per bale). Take more cores (20-40) in larger lots or if the hay is very variable.
• Use good technique - Probe the ends of bales near the center and at least 12 to 18 inches into the bale. The probe should be at a right angle to the bale end. Do not slant the probe or sample from the sides.
• Handle samples properly - Combine cored samples into a single sample and store it in a sealed freezer bag. Do not expose the sample to heat or direct sun and send it to the lab quickly. Moisture estimates are particularly prone to change in the sample before it gets to the lab.
• Not too big, not too small - The sample should weigh about a half pound (220 grams). If you get a larger amount, the diameter of your probe may be too large. Many labs will not grind a large sample, which defeats the purpose of careful sampling. Too small a sample will not adequately represent the hay lot.
• Split samples correctly - If you want to test the performance of a lab, send a fully ground and mixed sample to another lab. Never split an unground sample. Reputable labs will return your ground sample to you for further testing if you wish. (You should reject labs that are unwilling to do this).

Many disputes about hay testing results can be attributed to differences in sampling methods. The principle of hay sampling is to obtain randomly chosen samples, which represent the average composition of the hay stack or lot. Never present an un-cored sample to a lab such as a flake or a small handful of forage.

Research has shown that, if these simple guidelines are followed, reliable results can be obtained, even if you are using different probes or people. Nonetheless, a minimum of +/- 0.5 percent variation in results is normal and should be expected due to typical variations in sample and lab practices.

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Source: J.W. Schroeder, (701) 231-7663, jw.schroeder@ndsu.nodak.edu
Editor: Rich Mattern, (701) 231-6136, richard.mattern@ndsu.nodak.edu

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