Effects of dietary tannins on total and extractable nutrients from manure

The effects of condensed tannins on N dynamics in ruminants have been a topic of research for some time, but much less work has focused on their impacts on other nutrients in manure. A 4 × 4 Latin square trial was used to determine if intake of sericea lespedeza (; SL; a condensed tannin source), at 0, 10, 20, or 40% of the diet (as-fed basis), would affect concentrations of nutrients in manure and patterns of total excretion when offered with alfalfa (; ALF) to sheep. With SL additions, average daily manure production increased linearly ( ≤ 0.01), from 40 to 50% of the diet mass. The concentrations of total C, total N, soluble P, total and soluble Na, total and soluble S, total and soluble Mn, and total and soluble B in feces increased ( ≤ 0.05) while soluble N, total Ca, total and soluble Mg, soluble Zn, total and soluble Fe, total and soluble Cu decreased ( ≤ 0.02). Total P, total and soluble K, soluble Ca, and total Zn were less affected ( > 0.05). Comparing diets containing 0 to 40% SL, average daily outputs of total C, total N, soluble P, soluble K, total and soluble Na, and total Mn increased linearly ( ≤ 0.01) by 42.0, 71.2, 93.3, 45.2, 111, 148, and 52.4 percentage points, respectively. Total K, total and soluble S, soluble Mn, and total and soluble B increased quadratically ( ≤ 0.02) by 26.1, 52.3, 26.7, 147, 100, and 19.5 percentage points, respectively. Conversely, outputs of soluble Zn and total Fe decreased linearly ( ≤ 0.01), by -51.5 and -24.8 percentage points, while total Ca, total and soluble Mg, soluble Fe, and soluble Cu decreased quadratically ( ≤ 0.05) by -15.7, -12.3, -40.0, -89.9, and -60.3 percentage points, respectively. Outputs of soluble N, total P, soluble Ca, total Zn, and total Cu remained unchanged ( ≥ 0.14). Ratios of manure outputs to feed inputs for C, N, K, and B increased ( ≤ 0.02) but those for P and Mg were unchanged ( ≥ 0.10). Ratios of soluble to total manure outputs (S:O) increased ( ≤ 0.01) for P, Ca, Na, Mn; decreased ( ≤ 0.05) for N, S, Mg, Zn, Fe, Cu, and B; and were unaffected by treatment ( ≤ 0.16) for K. Decreasing S:O ratios are consistent with the formation of complexes that adsorb these nutrients to insoluble fiber fractions of manure and could thus affect mineralization rates. This study suggests that dietary tannins, found in forages like SL, can alter the concentrations, total excretion rates and throughput efficiency of nutrients in manure.