Estimation of true phosphorus digestibility and endogenous phosphorus loss in growing pigs fed conventional and low-phytate soybean meals.
This study reevaluated the method of regressing of total P output against dietary P intake to simultaneously estimate true P digestibility and endogenous P loss in growing pigs fed either conventional or low-phytate soybean meal (SBM). Four isocaloric diets were formulated to contain increasing concentrations of each type of SBM (8 diets total), and therefore contained increasing concentrations of dietary P. Dietary P and Ca concentrations were deficient because they were supplied solely by SBM, and Ca:total P ratios were less than 1:1. Sixteen barrows (initial BW 17.7 +/- 1.8 kg) were surgically fitted with a simple T-cannula at the distal ileum, randomly assigned to metabolism crates, and fed the experimental diets in a replicated 8 x 8 Latin square design. Feed was provided at 90 g/kg of BW(0.75) and fed in 2 equally sized meals at 0800 and 2000, with diets containing Cr sesquioxide (3 g/kg) as an indigestible marker. As the P concentration increased from 0.9 to 3.9 g/kg of DM, the apparent prececal P digestibility increased for conventional SBM (P < 0.05), but no relationship was observed for low-phytate SBM. The output of total P [mg/(kg of BW(0.75).d)], either prececal or total tract, exhibited a linear relationship (P < 0.01) with increasing P intake. However, a quadratic response (P = 0.02) was also detected for total tract P output from pigs fed low-phytate SBM. True P digestibility was not different between prececal and total tract collection sites (P > 0.10), but was greater (P < 0.01) for low-phytate SBM (62.6%) compared with conventional SBM (44.5%). Endogenous P estimates were not different between the SBM varieties and averaged 4.83 mg/(kg of BW(0.75).d). However, endogenous P estimates were highly variable between individual animals and, therefore, were not significantly different from zero. In this study, estimates of endogenous P loss from pigs were relatively low compared with previously reported values, and evidence of nonlinearity in P output was observed. These results suggest that the difference in true P digestibility between conventional SBM and low-phytate SBM is influenced by dietary phytate content when growing pigs are fed P-deficient diets.
Dilger
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Department of Animal Sciences, Purdue University, West Lafayette, IN 47097-2054, USA.
Adeola
O
O
D000821:Animal Feed / Q000032:analysis; D000818:Animals; D004032:Diet / Q000662:veterinary*; D004063:Digestion / Q000502:physiology*; D004435:Eating; D041981:Gastrointestinal Tract / Q000378:metabolism; D016014:Linear Models; D008297:Male; D010758:Phosphorus / Q000378:metabolism*; D016226:Phosphorus, Dietary / Q000378:metabolism*; D010833:Phytic Acid / Q000008:administration & dosage* / Q000378:metabolism; D011897:Random Allocation; D013025:Glycine max / Q000378:metabolism; D013552:Swine / Q000254:growth & development / Q000378:metabolism*
D016226:Phosphorus, Dietary; D010758:Phosphorus; D010833:Phytic Acid