Can Forage Tannins Reliably Improve Protein and Nitrogen Utilization on Confinement Dairy Farms?.

This presentation will review studies with birdsfoot trefoil (BFT), which assessed the potential impacts of incorporating forages with <30 g/kg of condensed tannins (CT) onto dairy farms. Work included the development of a modified acetone-butanol-HCl assay to improve the accuracy of estimating CT in forages. Multistate studies indicated CT deposition in BFT was highly influenced by plant genotype, plant maturity, and growth environment. Commonly used in-situ and laboratory methods gave markedly different estimates of degradable protein in BFT, thus improved assays must be developed for formulating rations with CT-containing forages. While consistently restricted by CT, degradable protein was also markedly influenced by growth environment and forage conservation method. In three feeding trials, Holstein cows produced 1.5 to 3.8 kg/day more energy-corrected milk (ECM) when fed total mixed rations formulated with BFT in place of CT-free alfalfa. The concentration of CT in BFT needed to maximize ECM, however, differed among trials, ranging from 10 to 25 g/kg. Cows fed BFT had lower milk urea N and greater milk protein secretion indicating greater protein-use efficiency. Total manure N excretion was similar among diets, but CT in BFT reduced urinary N, which in turn decreased ammonia losses from simulated barn floor or soil surfaces by up to 40%. When collected and applied to cropland with minimal ammonia loss, manure from BFT and alfalfa diets produced similar DM yields of corn silage. Terminated stands of BFT and alfalfa also supported comparable DM yields of sorghum-sudangrass, suggesting that CT did not adversely affect N availability to crops. Our results suggest that forages with <30 g/kg CT can improve milk production and reduce ammonia losses from dairies without affecting crop production. Improved laboratory assays and strategies for improving the nutritional uniformity of CT-containing forages will, however, be needed to maximize their utility for dairy farms.