Hay testing is always valuable, but it is especially helpful when using crop residues and developing diets to stretch limited hay supplies. Before sending a sample in for analysis, it is always good to visit with a nutritionist to see what labs they recommend and what tests would be most appropriate for the sample being analyzed. After tests have been paid for, it can be very frustrating to find out the test results are not helpful in making decisions.
In general, a hay probe should be used to collect a composite sample from at least eight to 10 bales for analysis. The hay should at least be analyzed for crude protein (CP), acid detergent insoluble CP, neutral detergent fiber (NDF), NDF digestibility, crude fat and ash. Minerals, nitrates, hydrogen cyanide (prussic acid) potential and other analysis can be added when desired based on each situation.
Key pieces of information from the analysis to look at are total digestible nutrients (TDN), adjusted CP and ash content. TDN is the common term used to describe the energy content of cattle feed. Adjusted CP accounts for any heat damage that makes CP unavailable to the animal.
Labs use different equations to estimate TDN, so values can vary significantly from lab to lab. To get the best estimate of TDN, samples should be sent to labs like Dairy One or Cumberland Valley that use summative equations. Summative equations can account for differences in NDF digestibility and ash content, which can have huge impacts on TDN. Ash content includes the minerals in the forage as well as any soil contamination and is best analyzed by wet chemistry analysis.
The importance of using a summative equation and getting a wet chemistry estimate of ash content is highlighted by the results below for a sample of cornstalks. When an appropriate ash value was not included in the summative equation, TDN was estimated at 57%. However, when the actual ash content of 18.21% was included, the TDN value was only 46%.
If forages are being tested for nitrates, it would be advisable to also test them for hydrogen cyanide potential, based on recent research. Hydrogen cyanide potential decreases as plants mature, so it is generally not common in hay but appears to have been an issue in a few situations. ServiTech labs have a good test for evaluating hydrogen cyanide potential.
