Forage Nutritive Value over Time in a Reduced Lignin Alfalfa Cultivar.

Forage nutritive value is important for maintaining high production in ruminant animals. Alfalfa (Medicago sativa) digestibility declines as the plant matures due to lignification in secondary cell walls. Scientists at Forage Genetics International, The Samuel Robert Noble Foundation and U.S. Dairy Forage Research Center collaborated to modify lignin content in alfalfa through genetic modification. The hypothesis is that this new cultivar should maintain acceptable nutritive value longer than conventional alfalfa cultivars. The objective of this research was to evaluate the change in nutritive value over time of HarvXtra^TM alfalfa compared with conventional cultivars. Field trials were established in six states (KS, MI, OH, PA, CA, WI) in Spring 2015 with three alfalfa varieties: cv. HarvXtra-008 is the reduced lignin cultivar, cv. 54R02 was selected for high yield, and cv. WL 355RR was selected for high nutritive value. A RCBD was used with three or four replicates. Growth cycle sampled was the main plot factor and alfalfa cultivar was the subplot factor. Growth cycles in the seeding year plots were hand sampled at 20, 23, 27, 30, 34, and 37 days of regrowth to a 5-cm stubble height. Samples were prepared and analyzed by calibrated Near Infrared Spectroscopy. Sample date x cultivar interactions (P > 0.15) were not found for neutral detergent fiber (NDF) and only at MI in the second growth cycle for NDF digestibility (NDFD). HarvXtra-008 was consistently higher (P < 0.05) in NDFD (+49.6 g/kg) and lower in NDF (-29.6 g/kg) than the other two cultivars across locations and dates. In 2016 Ohio data, mean stage weight for HarvXtra-008 across all harvest schedules was statistically lower (P < 0.05) than WL 355RR and 54R02 and leaf proportion for HarvXtra-008 and WL 355RR were consistently higher than 54R02 (P < 0.05). The experiment is continuing at all six sites in 2016.