New crop hay will start hitting the hay auctions in the next few weeks and it will be important for buyers to understand the value of accurate nutrient testing. Plus, now is a good time to review sampling protocols. Even the best nutritionist can’t balance a ration properly if he or she has flawed test information.
Hay sampling contributes the largest share the variation in hay testing, typically more than the variation between labs. Forage quality often determines between 20 and 50 percent of hay value in most areas, particularly alfalfa hay for dairy buyers. Consequently, lab results are often subject to scrutiny by buyers and sellers, and can be the cause of disputes with the problem generally tracing back to differences in sampling.
Variation is caused by differences between leaf and stem in different parts of a bale, the presence of weeds, baling conditions and other factors. A small amount of variation between samples is normal, but if sampling protocol is carefully followed, sampling variation can be reduced to an acceptable level, and the potential forage quality successfully predicted.
It is important to sample the hay either as close to feeding, or as close to point of sale as possible. Dry matter (DM) measurements are especially subject to changes after harvest and during storage, but other measurements may also change. Hay immediately after harvest normally goes through a process of further moisture loss known as a ‘sweat’. During this period, hay may heat up due to the activities of microorganisms, driving residual moisture from the hay. Thus, moisture content is likely to be reduced in the days and weeks after harvest.
If the hay has been baled with excess moisture, further biological activity may result in molding, and under very high moisture conditions, spontaneous combustion. After hay has equilibrated to about 88-90 percent dry matter (10-12 percent moisture, depending upon humidity), it is typically quite stable. ‘As received’ dry matter measurements should be used to adjust quantity (tonnage, yield), not quality parameters, which should be compared on 100 percent DM basis.
Following these protocols will give producers an accurate read on hay quality.
- Identify a single ‘lot’ of hay.
This is a key first step to proper hay sampling, and one frequently ignored. A hay lot should be identified, which is a single cutting, a single field, variety, or truck load and generally less than 200 tons. Combinations of different lots of hay cannot be represented adequately by a forage sampling method; different lots must be sampled separately. Don’t mix cuttings, fields, or hay types.
- Choose a sharp, well-designed coring device.
Use a sharp coring device 3/8-3/4” diameter. Never send in flakes or grab samples, it is nearly impossible for these samples to represent a hay lot. “Hand-grab’ samples from bales have been shown to be significantly lower in quality than correctly sampled forage. The corer should have a tip 90o to the shaft, not angled, studies have shown that angled shafts push aside some components (mostly stems) of hay, providing a non-representative sample of the entire mix. Too large diameter or probes greater than 24 inches provide good samples, but give too much forage in a 20 probe composite sample with the sampler often stopping before 20 cores are completed or the lab may not grind the whole sample. A range of probe tip designs have been used successfully, from serrated to non-serrated tips, with the most important aspect being that the tip be sharp and not create ‘fines’ during sampling.
- Sample at random
Walk around the lot as much as possible, and sample bales at random making sure that both sides are sampled if possible. This may be difficult, since some of the bales may not be available to the sampler (against walls of a barn or up too high for practical sampling). However, the sampler should make every attempt to sample in a random fashion so as not to bias either for or against any bales in the stack. For example, walk 15 steps, sample, walk 20 steps, sample, walk 5 steps, and sample; while walking around the stack try to represent all areas of the lot. Don’t avoid or choose bales because they look especially bad or good. If 20 cores are taken, they won’t make much difference anyway.
- Take enough cores
Twenty cores are recommended for a composite sample to represent a hay lot. This is the same for a lot of large bales or small bales. This is because core variation in forage quality is tremendous. Sampling a large number of locations and bales to create a composite sample is a key aspect of representing the full variation contained in a hay lot.
- Use proper technique
Sample butt ends of hay bale, between strings or wires, not near the edge. Probe should be inserted at 90o angle, 12”-24” deep. Do not sample in the same spot twice. Do not use any technique that is likely to misrepresent the leaf-stem ratio. The sides or the top of the bale should not be sampled, since these cores will only represent one flake from a single area of the field. With round bales, sample towards the middle of bale on an angle directly towards the center of the bale.
- Handle samples correctly
Seal the composite sample in a well-sealed plastic bag and protect from heat. Double bagging is beneficial, especially for DM measurements. Deliver to lab as soon as possible. Do not allow samples to be exposed to excess sun (e.g. in the cab of a pickup truck). Refrigeration of hay samples is helpful, however, dry hay samples (about 90% DM) are considered fairly stable.
- Choose an NFTA Certified Lab
The National Forage Testing Association, a volunteer group set up by hay growers, sends blind samples to labs, and they must match the true mean within an acceptable range of variation. See Iowa State University Extension publication Forage Testing Laboratories, for a list of commercial forage testing laboratories near you.