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Effect of diet composition and particle size on nutrient excretion of finishing pigs and the propensity to cause manure pit foaming
Manure pit foaming on commercial swine farms has been a significant problem in recent years. Changes in dietary fiber fermentability and lipid composition may alter manure composition resulting in increased manure foaming and methane production in anaerobic pits. The objective of this experiment was to measure nutrient excretion and manure foaming capability (MFC) of pigs fed 3 diets differing in the source and amount of NDF (% DM) and ether extract (EE; % DM) when ground to 2 particle sizes. Two groups of 24 growing gilts (initial BW =119.5 ± 8.9 kg) were placed into metabolism crates and randomly allotted to 1 of 6 diets (4 replicates/treatment/group). Dietary treatments consisted of 1) corn-soybean meal (7.2% NDF, 4.6% EE; CSB), 2) CSB + 35% DDGS (13.7% NDF, 6.2% EE; DDGS), and 3) CSB + 21% soybean hulls (20.0% NDF, 6.8% EE; SBH). Diets were ground to a mean particle size of 374 ± 29 µm (Fine) or 631 ± 35 µm (Coarse) and fed for 7 wk. Excretion of DM, NDF, and EE were measured after total feces and urine collection on d-21 to d-24. Feces and urine were mixed daily and stored in simulated deep pit storage tanks. The MFC of each sample was measured in the laboratory using a column and N bubbling. Data were analyzed using the MIXED procedure of SAS, with individual pig as a random effect and diet composition, particle size, and their interaction as fixed effects. There was a diet composition × particle size interaction for MFC (P < 0.05). Greater (P < 0.05) MFC was observed for pigs fed coarse SBH compared with fine CSB and SBH, but not for fine or coarse DDGS. There was no diet composition × particle size interaction for excretion of DM, NDF, or EE. Excretion of DM and NDF were greater (P < 0.05) in pigs fed DDGS and SBH than in pigs fed CSB. Excretion of EE was greater (P < 0.01) for pigs fed DDGS than CSB or SBH. Excretion of DM, NDF, and EE was greater (P < 0.05) for coarse compared to fine diets. These results indicate that fiber composition in soybean hulls has a greater impact on MFC than the fiber composition in DDGS, and larger diet particle size reduces DM, NDF, and EE digestibility causing increased content in manure and MFC.
Keywords: diet particle size, fiber, lipid, manure foaming, nutrient excretion, finishing pigs