Fecal phosphorus excretion and characterization from swine fed diets containing a variety of cereal grains

Authors: Leytem, April; THACKER, P - UNIV OF SASKATCHEWAN

Submitted to: Animal Feed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2008
Publication Date: 7/1/2008
Citation: Leytem, A.B., Thacker, P.A. 2008. Fecal phosphorus excretion and characterization from swine fed diets containing a variety of cereal grains. Animal Feed Science And Technology. 7(2):113-120.

Interpretive Summary: It has previously been thought that swine excrete large amounts of undigested phytate as they lack sufficient endogenous phytase enzyme to utilize this form of phosphorus (P) in grain based diets. We have previously characterized the P in swine feces from animals fed both a low phytate and normal barley diet and found very little phytate in the resultant feces. To determine if this lack of undigested phytate in the feces of swine fed barley based diets was due to endogenous phytase enzyme levels in the barley or due to phytase activity in the gut of the swine, we fed five cereal grain based diets with a range of endogenous phytase activity of 16 to over 100 FTU per kilogram of feed. There were four pigs assigned to each diet and diets were fed for a seven day acclimation period prior to sample collection. Fecal samples were collected for three days and pooled per animal. Total tract digestibility coefficients were determined for dry matter, P, and phytate and the fecal P characterized via 31P-NMR. Digestibility coefficients for P and phytate ranged from 0.11 to 0.46 and 0.94 to 1.00, respectively. There was very little phytate P excreted (< 6% of total P) from the swine irrespective of the dietary treatment, suggesting that in low P diets, swine have the ability to digest phytate in a range of cereal grains.

Technical Abstract: To determine the effects of cereal grain phosphorus (P) source on faecal P composition, twenty crossbred barrows, weighing 35.8 plus or minus 3.09 kg, were fed one of five diets with four pigs assigned to each of the diets. The diets contained corn, wheat, high fat-low lignin oat, normal barley or low phytate barley with the cereal grains supplying the sole source of dietary phosphorus. Diets were fed for a seven day acclimation period followed by a three day faecal collection. Total tract digestibility coefficients were determined for dry matter, phosphorus and phytate using the indicator method. Fecal phosphorus was characterized using solution state phosphorus nuclear magnetic resonance spectroscopy (31P-NMR). Water soluble phosphorus (WSP) and the ratio of WSP to total phosphorus (WSP:TP) were determined in the faeces. Digestibility coefficients for phosphorus and phytate ranged from 0.11 (corn) to 0.46 (wheat) and 0.94 (oat) to 1.00 (corn and low-phytate barley), respectively. There was very little phytate phosphorus excreted in the faeces regardless of the source of cereal grain (< 6% of total phosphorus), and phytate degradation was not related to the endogenous phytase level in the diet. There was a negative relationship between the faecal WSP:TP ratio and the concentration of phosphate monoesters in the faeces. In summary, our results indicated that the majority of the phosphorus in the faeces of pigs fed cereal grains was present in the form of inorganic phosphate and only trace amounts of phytate were excreted. This phenomenon did not appear to be related to the content of either phytate or phytase in the grain. Further research should be conducted with diets more typical of those used in commercial swine production to confirm these findings, as there could be greater potential than previously thought for off-site phosphorus losses when swine faeces are applied on agricultural lands.