Use New Forage Tests To Build Better Rations
Not all forage fiber is the same. And neutral detergent fiber (NDF) doesn’t tell you everything you need to know to formulate high forage diets for high producing dairy cows.
Total NDF is not a good predictor of animal performance, explains Dave Combs, dairy nutritionist at the University of Wisconsin. To understand how cows will perform when fed forage you need to know how fast the forage fiber is digested and how much of that fiber is not digestible (uNDF).
Research during the last decade has led to several new forage tests. Nutritionists can use these new tests to build better rations to optimize cow health and performance. The first step is learning a new alphabet. TTNDFD, aNDFom, and uNDF240 are just a few of the new tests available.
TTNDFD stands for total tract neutral detergent fiber digestion in ruminants. Researchers at the University of Wisconsin were looking for a quick, low-cost test that could accurately determine how fiber is utilized in cows. Previous in vitro tests looked at digestion at a given point in time, 24 hours, 30 hours, 48 hours but those tests did not correlate well to animal performance, says Combs. And uNDF is only part of the equation.
TTNDFD combines uNDF with rate of digestion to provide more accurate estimates of animal performance. The test utilizes an NIR scan to estimate the uNDF as well as the disappearance at 24, 30 and 48 hours. These four factors are combined to calculate the rate of digestibility. TTNDFD can be used to compare digestibility of two different forages in the diet such as alfalfa to corn silage. Previous tests such as NDFD30 only allowed users to make apples to apples comparisons such as alfalfa to alfalfa or corn silage to corn silage. Test results are generally available the same day the sample is received, provided it arrives before the cutoff time. The test is currently available at Rock River Laboratory in Watertown, WI, and the University of Wisconsin.
aNDFom is a modification of the NDF test with amylase, sodium sulfite and ash correction. aNDFom provides a more accurate measure of NDF. Making hay in a hurry, using big chopping equipment and flood irrigation all can lead to some soil contamination of forages. The problem is that soil does not solubilize in NDF solution, and the result is inflated NDF results. “Inflation of the NDF content means the diet as formulated is lower in actual NDF,” says Mike Van Amburgh, dairy nutritionist at Cornell University. Intake and rumen health can both be compromised when NDF is not accurate.
Nutrition software uses NDF to calculate energy from available carbohydrates and effective fiber. When ash and soil contamination are not accounted for the amount of NDF and therefore the amount of energy available and the digestibility will both be inflated. Van Amburgh recommends that nutritionists use aNDFom in place of NDF. Benefits include better rumen health through greater rumen fill and better predictions of energy and protein supply due to more accurate numbers.
Before new tests were developed uNDF240 was the best measure of unavailable NDF. The test was done through in vitro incubation under specific conditions. But 10 days is a long time to wait for test results and forages don’t stay in the cow that long anyway. Commercial labs now provide uNDF240 through NIR analysis.
Research at Cornell University with uNDF has identified fast and slow pools of NDF. While research is ongoing, the data so far suggests that uNDF240 may be useful to predict dry matter intake.
Getting fiber right pays
Producers have gotten really good at harvesting high-quality forages. But sometimes there is not enough fiber in those forages, or digestibility is too low to meet the cows’ needs in order to optimize cow health and performance, explains Combs. At a minimum, cows need 30% NDF in the diet for rumen health. Fiber digestibility should be at least 42% to 45%. Failure to meet these minimums in fiber requirements can leave a lot of money on the table.
In corn silage we know that if starch digestibility falls from 98% to 95% the loss is 2 to 5 lbs of milk/cow/day. The same is true with fiber digestibility. Every two to three unit decrease in fiber digestibility reduces milk production by 1 lb/cow/day, says Combs. Corn silage has a wide range of digestibility – 30% to 51% as measured by TTNDFD. When fiber digestibility is low you can easily lose 7 to 8 lbs of milk per cow per day. That’s a lot of money left on the table. The new tests can help you build better rations to capture some of that lost milk production.
To learn more about these new forage tests, please see these papers:
“Relationship Between NDF Digestibility and Animal Performance,” presented by David Combs at the Western Canadian Dairy Seminar.
“How do We Make Better Decisions in Dairy Cattle Diets and Management with Forages and Nitrogen,” presented by Mike Van Amburgh at the Northeast Dairy Producers Conference.