Multistate Evaluation of Reduced-Lignin Alfalfa Harvested at Different Intervals

Nutritive value of alfalfa (Medicago sativa L.) is limited by indigestible cell wall constituents, especially lignin. Commercially released genetically engineered alfalfa cultivars with reduced lignin (RL) concentration were developed recently by downregulation of the caffeoyl CoA 3-O-methyltransferase (CCoAOMT) enzyme in the lignin pathway. This research compared forage nutritive value and dry matter yield of a RL cultivar ('HarvXtra-008') with non-RL cultivars ('54R02' and 'WL355RR') across six states in the northern United States. A randomized complete block design with a split-plot restriction on treatment randomization was used, where harvest intervals (28, 33, and 38 d) were assigned to whole plots and cultivars were the subplots. Harvest interval and cultivar effects were significant (P < 0.001) for all variables, and cultivars responded similarly across harvest intervals in that forage yield increased and nutritive value declined with increasing harvest interval. HarvXtra-008 was consistently greater in forage nutritive value than non-RL cultivars averaged across harvest intervals: it was 8.4% lower in acid detergent lignin, 3.5 to 7.5% lower in amylase-treated neutral detergent fiber, and 5.3 to 7.7% greater in neutral detergent fiber digestibility, but 4.8 to 7.0% lower in dry matter yield. HarvXtra-008 was slightly higher or similar in nutritive value and had similar or greater dry matter yield compared with non-RL cultivars harvested on a harvest schedule 5 to 10 d earlier and more frequent. Thus, RL alfalfa can extend the time interval when it is possible to harvest forage with adequate fiber digestibility for animals with high energy requirements.