Dairy producers recognize the importance of high quality alfalfa in dairy cattle rations. High quality alfalfa in the ration provides protein, energy, and minerals and increases milk production while maintaining low feed costs and proper rumen function.
According to Michigan State University Extension, one of the most important factors in determining alfalfa quality is its maturity at harvest. As alfalfa matures, its fiber content increases while its fiber and dry matter digestibility decrease. On the flip side, if alfalfa is harvested at an immature stage it becomes difficult to feed because its fiber level is too low for most high-producing cows. Also, the yield of the first cutting of alfalfa is typically the largest of the year accounting for 35-40 percent of the year’s total crop. Thus, timing of first harvest is always a balance between these two nutritional factors, plus early harvest tends to lower the life of alfalfa stands.
When alfalfa is fed to high producing lactating dairy cows the goal is to harvest it at 40 percent neutral detergent fiber (NDF) content. At this fiber content the dairy producer and dairy nutritionist are provided with a feed that gives the cow adequate fiber for normal rumen function and maintains high feed intake necessary for good milk production. It also provides flexibility to keep the cow’s ration at the proper energy density, keep protein supplementation at a reasonable level, and maintain good overall animal health. For a more complete discussion of these very important issues I recommend reading “Timing Spring Alfalfa Harvest—The Final Word?” an excellent Michigan State University publication.
Usually the yield of alfalfa dry matter is the highest at the first cutting, thus, timing first cutting to get an optimal NDF level is very critical. Currently the best method to use for timing optimal first cutting is harvesting based on accumulated growing degree days (GDD). Growing degree days are a temperature-based index measuring the amount of accumulated heat the crop has been exposed to during the first portion of the growing season. Growing degree days are calculated by averaging each daily minimum and maximum temperature beginning March 1, then subtracting the base temperature of 41 degrees F to get the number of GDD’s for each day, then keeping a running total. Daily GDD for days with an average temperature of less than 41F are not counted. Research, much of it performed by Michigan State University scientists, has shown that in the upper Midwest alfalfa averages about 40 percent NDF when 750 GDD’s are accumulated. It takes an additional 220 GDD to reach 45 percent NDF, thus, beginning harvest at 750 GDD’s will give about a 7-day window to complete alfalfa harvest before 45 percent NDF is reached (unless weather is abnormally hot).