A good hay test can prove valuable when designing a winter feeding program. There can be a lot of information on a hay test, and knowing which numbers to focus on may not always be clear. For most producers, the first items to look at should be adjusted crude protein (CP) and total digestible nutrients (TDN).
Some labs will report values on both an as-fed and dry matter (DM) basis. For example, adjusted CP may be listed at 10 on an as-fed basis and 11.1 on a DM basis. The value in the DM column should be used when comparing different hays to each other or to nutrient requirement tables. Comparing samples based on the as-fed values can be misleading.
You may be wondering what the difference is between CP and adjusted CP. Hopefully, when you look at your hay report, the values for CP and adjusted CP are the same. However, in some cases the adjusted CP value will be lower than the CP value. When this occurs, it indicates that the hay was likely baled a little too wet and went through a heating process that made some of the protein and carbohydrates in the hay less digestible. To account for this reduction in protein digestibility, the lab will adjust the protein value down.
When feeding free-choice, hay that contains 12.5% protein or more on a DM basis will meet the needs of most lactating cows. Hay that contains 9% protein will meet the needs of most nonlactating cows in late gestation. When hay is the main component of the diet, there is no benefit to having hay with adjusted CP levels above about 14%.
The energy content of a hay or feed can be reported in a few different ways including TDN, net energy for maintenance (NEm), net energy for gain (NEg), etc. It is not necessary to look at all the different terms used to describe the energy content of a hay because they are all related. In terms of TDN, the higher the number, the better. Not all forage testing labs calculate TDN the same, so make sure to visit with a nutritionist about what lab to use and what tests are most appropriate for your hay sample.
Relative feed value (RFV) can be very misleading when comparing hay samples. Adjusted CP and TDN are much better indicators of hay quality and animal performance.
