GDD Relationship to Alfalfa Harvest

Ideally, alfalfa should be harvested at the lowest fiber content where it will provide adequate dietary levels and allow a reasonable grain amount to be added to maximize the dairy animal's energy intake and milk production. This generally ranges from 40 to 45 percent neutral detergent fiber (NDF), according to dairy nutritionists at Michigan State University. That NDF percent is generally reached at around an accumulation of 750 growing degree-days (GDD) base 41 degrees F.

The GDD accumulations are posted each Thursday on the World Wide Webb at http://www.agweather.geo.msu.edu in the "current weather" category under which is listed the "Base 41F Growing Degree Day Accumulations for Alfalfa Harvesting." If you don't have internet access you can contact Dennis Pennington.

Mike Allen, MSU Extension dairy animal nutritionist, says for an initial NDF content of 40 percent, growers should start cutting alfalfa 750 GDD, base 41 degrees F. It will take about 220 additional GDDs to reach 45 percent NDF. Producers who store alfalfa in a horizontal silo, or are feeding it in a high NDF and low protein diet, should start cutting at 680 GDD, base 42 degrees F, which corresponds to 38 percent NDF. He suggests producers begin tracking the GDD accumulation daily in their region at 550 until the optimum time approaches to begin harvest.

Allen points out the system is not perfect but it is probably better than relying on calendar days to manage alfalfa harvest. MSU Extension meteorologist Jeff Andresen, says growers should be aware that GDD accumulations had reached values as high as 170 by the end of March across the state's southern sections and may have to be taken into account when looking at the GDD numbers on the Webb.

Generally, northern Michigan's growing conditions are currently running about three weeks ahead of normal. In southern Michigan, growing conditions are about 1.5 weeks ahead of normal, according to Andresen.

For more information contact:

Dennis Pennington
Barry County MSU Extension
206 W. Court Street
Hastings , MI 49058
Phone: 269-945-1388
Fax: 269-948-3323
Email: pennin34@msu.edu
Web: www.msue.msu.edu/barry

MSU is an affirmative action, equal opportunity institution, Michigan State University Extension programs and materials are open to all without regard to race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, marital status, or family status. Issued in furtherance of MSU Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Margaret A. Bethel, Extension Director, Michigan State University, E. Lansing, MI 48824