ADF, NDF, RFQ, RFV
What do all those numbers on forage analysis results really mean? What can we do to improve them? Marvin Hall, Penn State explained the details of forage analysis and what producers can do to improve their forage quality at a recent Penn State Extension study circle for organic crop and dairy producers “High Quality Forage for Organic Dairies” in Parkesburg, PA.
We all know that dairy cows perform better (make more milk) on higher quality feed. But what makes one feed higher quality than another? Dr Hall explained that, in general, feed is higher quality if it consists of more highly digestible material. Sugars, starches and proteins in the plant are easy for animals to digest. Even non-ruminants, like people, can digest them. But plants also have cell walls that vary in digestibility. When the plant cell is young, it consists mainly of cellulose and hemi-cellulose which are readily digested by microbes in the rumen. However, as the cell walls age a substance called lignin is added to the cell walls which makes them less and less digestible. Lignin is what allows the plants to stand up. Lignin is not digestible.
A typical forage analysis has numbers for:
Crude Protein
ADF (acid detergent fiber); the amount of cellulose + lignin in the forage (cell wall).
NDF (neutral detergent fiber); the amount of cellulose + hemi-cellulose + lignin in the forage.
These are numbers based on lab tests. For example ADF is a test which uses an acid detergent that breaks down hemi-cellulose. The ADF and NDF tests tell you how much of your forage is made up of very digestible not so digestible material. The results can be used to calculate relative feed value (RFV) and a number of other indicators of feed quality.
So what does a GOOD forage analysis look like? Dr Hall says that in general you can follow the 20:30:40 rule. If you have about 20% Crude Protein; 30% ADF and 40% NDF you are in pretty good shape. Higher numbers for ADF or NDF mean the forage digestibility is declining and the forage is not as good.
While ADF and NDF give an indication of how digestible the forage is, they do not tell you exactly how digestible the cell wall is in the rumen. Recently, labs are using new tests NDFD (Neutral Detergent Fiber Digestibility) to measure the digestible of the cell wall. They use this number to calculate relative feed quality (RFQ). RFQ takes into account how digestible the digestible part of the feed is, as well as how much there is. Depending on the lab you work with this test might be standard or an additional fee. But, according to Dr. Hall it is likely well worth the additional $5. So let's take a look.
In the mid-west hay is often sold according to standards based on the RFQ. In PA we might be a little behind the times since a lot of feed is sold according to protein levels and relative feed value (RFV) only. New research based on feeding studies shows that RFV that does not take into account digestibility may underestimate the potential milk production for grass hay. Keep in mind these are all relative measures. But if you are comparing a grass to a legume hay, RFQ will give you a better measure.
What are some management suggestions to get the best Relative Feed Quality (RFQ)?
1. The number one factor according to Dr Hall is plant age. As plants mature beyond bud (legumes) or boot (grasses), the plant cells get old and start to have more and more lignin. Yield may continue to increase until flower but quality will be decreasing as the plants mature.
2. Watch your mechanical management. It is important to think about when you are raking and tedding your hay. You don’t want to do this when the plants are at less than 40% moisture or they will lose a lot of leaves which contain the most digestible material and protein. If they have already dried past this point raking with a little dew can make a difference.
3. Farmers can also chose alfalfa varieties that do not lose quality so quickly as they age. These varieties are usually designated with an initials HQ in their name.
DuPont, T.; Hautau, M; Hall, M. Penn State Extension
