You've got hay with a RFV value of 90 and one with an RFV of 134. Which one do you feed to milk cows? To pregnant beef cows or ewes in the last trimester? Which one could you get by feeding to dry cows and ewes early in the gestation cycle?
First, you need to know what RFV means. "It stands for relative feed value," says Chris Parker, Morgan County Extension ag educator. He works with farmers in his area with livestock to help them understand feedstuff reports from labs. Often the results are on a forage. In Parker's office is a hay probe available for use by anyone in the county. It attaches to either a bit and brace or an electric drill. Most county extension offices in Indiana have such a probe for loan so you can collect a good forage sample and have it analyzed," Parker says.
Factors feeding into RFV include crude protein content, acid detergent fiber and total digestible nutrients. The RFV value helps you compare one feedstuff to another. That's useful when trying to decide when to feed a certain type of hay.
Labs determine RFV values by running what's called Near-infrared analysis. Purdue University doesn't' do the tests, but you should be able to get a list of labs that perform such services from the county Extension educator. Samples run about $15 each.
So what are the answers to the questions? You would definitely choose the hay with a 134 RFV to feed to lactating dairy cows in full production," the Extension educator says. "That is good hay. Crude protein is likely in the 16 to 18% range, and fiber is relatively low compared to other types of hay."
You don't have to have a pure legume, such as straight alfalfa, to get these kinds of scores. A mixed hay with legume and grass can reach that level. Part of the secret is cutting at the right time. You want to cut before just as the grass begins to head out and before many alfalfa blooms are present. Tonnage may not be as high following such a plan, but quality will be much higher.
Pregnant animals as they approach the end of gestation also need good hay with plenty of energy, Parker says. On the other hand, animals which are just maintaining themselves, such as beef cows in the early stages of gestation, could get by on the hay with the RFV of 90. If you have that type of hay, feed it first before calving approaches, Parker advises. If you're buying it, don't necessarily pass sit up, but pay less for it and know what you're going to feed it to before you buy it.