The lab conducts feed analyses and recently began using the digestible organic matter index (DOMI), a formula created by Cumberland Valley Analytical Services (CVAS), a major feed analytic lab in Maryland.
New Index for Ranking Forage Quality
Digestible organic matter index gives a more accurate indication of hay value because it removes the ash and indigestible fiber from the equation.
When selecting hay to purchase, or testing hay, stockmen often use analytical tests to check crude protein (CP) levels and fiber components [acid detergent fiber (ADF) and neutral detergent fiber (NDF)]. Some laboratories use an index system that facilitates comparing the nutrient value of various batches of hay. The index provides one number that predicts quality of a hay sample, making it simpler to evaluate and compare forages.
Two indexes have been used for several decades. RFQ (relative feed quality) is a good equation, but costly. Most people use relative feed value (RFV) when evaluating forages. RFV has been the industry standard for more than 20 years.
However, a newer index works better, according to veterinarian Fred Muller and ruminant nutritionist Lynn Van Wieringen at Ag Health Laboratories in Sunnyside, Wash. Their lab conducts feed analyses and recently began using the digestible organic matter index (DOMI), a formula created by Cumberland Valley Analytical Services (CVAS), a major feed analytic lab in Maryland.
The DOMI gives a more accurate indication of hay value because it removes the ash and indigestible fiber from the equation. It evaluates digestible organic matter, which contains nutrients such as crude protein and readily available carbohydrates.
Van Wieringen says an index value — just one number — is handy, rather than having to compare multiple numbers.
“If you are looking at different alfalfa hay samples, for instance, you might look at various nutrient analyses, but it is nice to have one number to help with the ranking,” she says.
“We’ve known for quite awhile that we need a different ranking system. One of the limitations when using RFV is that it merely looks at two fiber values — the ADF and NDF,” says Van Wieringen. “It doesn’t take into account other nutrients in the hay, such as crude protein or digestibility of the fiber. Another problem is that soil contamination (dust, etc., in the hay) will elevate ash content and can skew the RFV value downward. A large portion of the ash will show up as fiber in this test.”
By contrast, the DOMI gives a more accurate indication of hay value because it removes the ash and indigestible fiber from the equation. It evaluates digestible organic matter, which contains nutrients such as crude protein and readily available carbohydrates.
The DOMI is generally reported as pounds of organic matter per ton of feed.
“If you have a value of 1,300 pounds of digestible organic matter in a ton of hay, that would be better than hay with [a] 1,100-pound value,” says Muller.
“A slide presentation on our website (www.aghealthlabs.com/) includes a graph that shows DOMI vs. RFV on various samples. Forages that have RFV of 170 might have a wide spread in the DOMI. I use this chart to show people the variation between what the old RFV would tell you and the actual DOMI. Some of those feeds have very good DOMI numbers, and some might not be as good as the RFV predicted,” explains Muller.
“If you pick a single DOMI and then look at the range of RFV on various forages, some will differ by 20 points. At 1,300 DOMI, some samples will be as low as 140 RFV and some as high as 160 RFV. So which are you getting? You don’t really know using the old index. We are excited about the DOMI as a better tool to help people buy better feed than we were able to predict with the old RFV index,” he says.
“Our goal is to help people more accurately evaluate forages so they can select better quality purchased feed, or make better plans for feeding the various batches of hay they’ve harvested,” says Muller.
Editor’s Note: Heather Smith Thomas is a cattlewoman and freelancer from Salmon, Idaho.