Effects of Dietary Tannins on Total and Extractable Nutrients in Manure.

Sustainable intensification of agroecosystems may include integration of livestock and crops with a portion of the animal’s nutritional requirements derived from crops or residues and excreta nutrients recycled locally. While plant tannins, are known to influence ruminant nutrition less is known about their influence on manure. We employed a 4x4 Latin square sheep trial to determine if intake of Sericea lespedeza (Lespedeza cuneate, SL; a condensed tannin source), at 0, 10, 20, or 40% of the ration, would affect concentrations of total C, N, P, and B in manure and patterns of total excretion when fed with alfalfa (Medicago sativa). With SL additions, average daily manure production increased from 0.4 to 0.5 of the ration mass (dw). The concentrations of total C, N, and B in manure, daily outputs, (concentration X daily manure dry mass), and manure/feed ratios (O/I) for each element also increased. Concentrations of water-extractable N decreased with added SL, and thus accounted for a smaller proportion of the total N in manure (S/O), but with greater manure outputs, no significant variations of daily outputs occurred. Variations in concentrations of extractable B in manure were small, and daily outputs increased together with manure mass, but S/O ratios decreased. Manure concentrations, daily outputs, and O/I ratios for total P (P₂O₅) were not significantly affected by different rations, although highest outputs and ratios coincided with 40% SL additions. Conversely, concentrations, daily outputs, and S/O ratios of water-extractable P were all significantly increased by SL. Additions of SL resulted in greater throughputs of total C, N, B, and increased water-extractable B, and P in manure. Increasing O/I, together with decreasing S/O observed for N and B, are consistent with interactions with condensed tannins that affix these two nutrients to insoluble fractions of manure and could thus affect mineralization rates. This study suggests tannins affect manure quality and thus grazing ruminants on some crops or residues may result in significant variations delivery of organic matter and nutrients to soil.