WHAT IS THE RFV?
Now that you know the basics of lab tests, I wanted to talk to you about one of the three main metrics for knowing the quality of your hay - relative feed value (RFV). This is the basic metric everyone wants to know when they ask about hay. It's like when people ask about the performance of your favorite football team, you can talk about the offense or defense, but everyone wants to know how many wins to losses you have.
(RFV) is an index which combines estimates of digestibility (Digestible Dry Matter, DDM) and intake (Dry Matter Intake, DMI). It pretty much tells how how well your livestock will eat the hay. Low RFV means they'll eat less and fill up quicker (but consume fewer nutrients) and a high RFV means they will eat more and digest their hay easily (while consuming more nutrients). So here's the equation:
RFV = DDM x DMI/1.29, where DDM = 88.9-(.779 x%ADF) and DMI= 120/%NDF. Doesn't that look fun? Okay, maybe not.
So if you have an ADF of 29.48 and an NDF of 35.84, you'll get an RFV of 171.1. Pretty good score. For dairy heifers RFV <130 is utility, 130-150 is fair, 150-170 is good, 170-185 is excellent, and 185+ is supreme. Keep in mind they need a higher RFV because they're producing milk. For horses, they just need enough fuel. 150+ is more than enough for horses though. Keep in mind the equation doesn't account for CP. That is why RFV is a good indicator of the quality of hay but it doesn't necessarily give you the whole picture. That is why we also look at the RFQ and TDN. I'll get to those in a later post.