Nutrient excretion and odorant production in manure from cattle fed corn wet distillers grains with solubles
2009
Spiehs, M.J. | Varel, V.H.
Twenty-four cross bred steers (BW 452.5 ± 15.5 kg) were used to evaluate nutrient excretion and odorous compounds in urine and feces of feedlot steers fed diets containing corn wet distillers grains with solubles (WDGS). Cattle were weighed, blocked by BW, and assigned randomly to 1 of 4 dry-rolled corn-based diets containing 0, 20, 40, or 60% WDGS (DM basis). A 96-h total fecal and urine collection was conducted. Orts, feces, and urine were collected daily. Samples were analyzed for moisture, total N, total P, water soluble P, and total S. Fresh fecal samples were collected at the end of the balance trial for analysis of VFA, phenol, p-cresol, indole, skatole, ammonia-N, and lactate concentration. Total P, N, and S intake increased linearly as the amount of WDGS increased in the diet (P [less-than or equal to] 0.02). Total P excretion increased linearly (P < 0.01), attributed to a significant linear increase in urinary P excretion as the amount of WDGS increased in the diet (P = 0.02). Water-soluble P excretion in feces was similar for cattle fed all 4 diets (P greater-than-or-equal 0.11). Total N excretion increased linearly as dietary WDGS inclusion increased (P < 0.01) and was due to a linear increase in urinary N excretion (P < 0.01). Total S excretion also increased as WDGS concentration increased in the diet (P < 0.01). Dietary treatment did not affect the concentration of odorous compounds in urine (P greater-than-or-equal 0.07). Total VFA concentration in feces decreased as WDGS increased in the diet (P < 0.01), but branched-chained VFA concentrations (isobutyrate and isovalerate) and phenol in feces increased when WDGS replaced corn in the diet (P [less-than or equal to] 0.04). There was no difference in the concentration of the other aromatic compounds (p-cresol, indole, skatole) in feces from cattle fed the 4 dietary treatments (P greater-than-or-equal 0.09). This study indicates that feedlot cattle fed increasing amounts of WDGS had increased P, N, and S intake and excretion, which may contribute to the production of odorous compounds (primarily long- and branched-chain VFA, and phenol) as well as increased ammonia and H₂S emissions from the feedlot. Increased P concentration in livestock waste will increase the amount of land necessary to utilize manure P. Because of increased urinary P excretion, producers should consider environmental implications of liquid runoff from the feedlot surface as well as solid manure when WDGS are fed to feedlot cattle.
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