While farmers were fretting about the cool spring weather and early rains delaying corn planting, first cutting got ahead of many people. Late planting will likely present its own challenges when corn silage harvest begins this fall, but dairy farmers are already trying to find ways to cope with the quality of first-cutting hay. That’s according to Stuart Rymph a dairy nutrition and technical services specialist with Purina Animal Nutrition based in Wisconsin.
The upside, Rymph says, is that with a relatively cool spring, lignin levels in alfalfa should have been lower and neutral detergent fiber digestibility (NDFd) higher than normal for a given stage of maturity. However, the actual alfalfa maturity at harvest was much more advanced than normal, more than offsetting any potential gains from the cool weather. He explains that high NDF coupled with lower NDF digestibility means forages will have more “fill” effect; passing out of the rumen more slowly as it takes longer to digest, potentially reducing total dry matter intake (DMI). “With lower NDF digestibility, farms will probably not be able to push as high a percentage of forage as they did the last couple of years,” he says. This will require you to work closely with your farm clients in testing feedstuffs.
Most forage-testing labs now offer some type of NDF digestibility test — usually based on some variation of an in vitro (in glass/flask) digestibility. The very nature of the in vitro tests, using rumen fluid to ferment samples, can introduce significant variability — both from lab to lab and also between runs at the same lab. Near Infrared (NIR) tests can be much more consistent (repeatable) but they are just correlations and calculations based on the in vitro runs ― so variation among the original in vitro runs is still inherent in the NIR results. “Ranking feeds by NDFd categories works better than thinking the latest number is ‘exact,’” notes Rymph.
“Because of this variability, comparing sample results from two different labs doesn’t really tell you much,” he says, recommending that dairy producers and nutritionists stick with one lab and one incubation period (12, 24, 30 or 48 hours) for all testing. This will provide the nutritionist and producer with relative comparisons to assess forage digestibility.