79 April 17-19, 2017 Tri-State Dairy Nutrition Conference Agronomic and Nutritional Attributes of Reduced Lignin Alfalfa R. Mark Sulc 1,2 , Angela Parker 2 , Kenneth Albrecht 3 , Kim Cassida 4 , Marvin Hall 5 , Doohong Min 6 , Steve Orloff 7 , Xuan Xu 6 , and Dan Undersander 3 2 Dept. of Horticulture and Crop Science, The Ohio State University 3 Dept. of Agronomy, University of Wisconsin-Madison 4 Dept. of Plant, Soil and Microbial Sciences, Michigan State University 5 Dept. of Plant Science, Pennsylvania State University 6 Dept. of Agronomy, Kansas State University 7 University of California Cooperative Extension, Siskiyou County 1 Contact at: 2021 Coffey Road, 202 Kottman Hall, Columbus, OH 43210-1086, (614) 292-9084, email: sulc.2@osu.edu. Abstract Alfalfa (Medicago sativa) growers are faced with the recurring dilemma of having to balance yield and forage quality when harvesting their alfalfa crop. Yield increases while digestibility decreases as the plant matures, primarily because of increasing lignin content in the stems. A consortium of scientists at Forage Genetics International, The Samuel Robert Noble Foundation and U.S. Dairy Forage Research Center collaborated to alter the lignin content in alfalfa through genetic modifcation, resulting in the recent commercial release of the HarvXtra ® alfalfa brand. A number of alfalfa varieties having the reduced lignin HarvXtra ® trait are being marketed. Reducing the lignin content in alfalfa should extend the time interval when forage can be harvested and still maintain adequate nutritive value for ruminants with high nutritive requirements. Field trials were established in 6 states (KS, MI, OH, PA, CA, and WI) in spring 2015 to evaluate yield and nutritive value over time of the transgenic HarvXtra-008 alfalfa variety compared with 2 other varieties (one selected for high quality and one for high yield). Forage samples were collected over time during 2 growth cycles in 2015 and analyzed for nutritive value. Forage yield and nutritive value were also evaluated under 28, 33, and 38-day cutting intervals in 2015. Across all 6 states in the seeding year, HarvXtra-008 forage had consistently lower neutral detergent fber (-2 to -3.8 units of NDF), lower acid detergent lignin (-1 unit of ADL), and higher NDF digestibility (+4.2 to +5.4 units of NDFD) compared with the other alfalfa varieties. This represents a 7 to 10 day advantage in nutritive value for HarvXtra-008. When cut on the 38-day schedule, HarvXtra-008 yielded similarly or more and often had higher nutritive value than the other varieties cut more frequently on 33- or 28-day schedules. Results with HarvXtra-008 from the frst year are promising for alfalfa growers who want to maintain high forage nutritive value while increasing forage yields with less frequent harvests. More years of data will show how harvest interval affects nutritive value, yield, stand persistence, and proftability of alfalfa with the reduced lignin transgenic trait. Introduction Alfalfa is a high-yielding forage legume with nutritional attributes that complement those of corn ( Zea mays L. ) silage when used in dairy rations. Morphological and physiological changes occur in the plant as it matures that increase yield of DM per acre but decrease the nutritional value of the forage. As alfalfa approaches the ideal time for harvest, its nutritional value declines on a daily basis due to the accumulation of indigestible plant constituents in the cell walls. The yield