Hay is a cornerstone in the diet of many farm animals, including cows, sheep and horses. It is impossible to tell the quality of hay from appearance alone. Testing for hay gives insight into its nutritious value and protein content, and can uncover issues such as mineral imbalances that can degrade an animal's health. If you grow hay to sell it as feed for animals, you can use the results of hay testing to prove your product is high-quality and command a higher price.

Penetrate the bale of hay with a hay probe, also known as a hay corer. The probe should have a diameter of 3/8 to 3/4 inch. Push the sharp tip 12 to 18 inches into the bale at a 90-degree angle. According to the Forage Extension Program at Montana University, you should probe square bales near the center on their ends, while it is better to take a sample from the round edges of round bales.

Rocky Mountain Research & Consulting, Inc. recommends sampling at least 15 bales at minimum to get an idea about the average quality of hay. The group also advises that you can borrow a hay probe from "a hay broker, a county extension agent, or agricultural professional." As of 2008, you could purchase the tool for around $100.

Mix the samples from each lot of hay and seal them in a plastic bag. Do not mix hay from different lots or of different types. Double-bag the samples to further protect them. Label each bag so you know which sample originated from which lot. Keep the bags out of the sun and away from heat.

Contact the testing lab to determine the information you must include with your package, how the lab performs tests and how long you can expect the results to take. Ship your hay samples to the laboratory for testing using a delivery service such as UPS or the United States Postal Service. The laboratory will test for crude protein (CP) and can also test for nutritious elements including acid detergent fiber (ADF) and neutral detergent fiber (NDF).