25 Measuring Intestinal Permeability When Urine is not an Option

Abstract

Abstract The need to understand intestinal health is of increasing importance as the livestock industry seeks to maintain performance efficiency while eliminating prophylactic antibiotic usage. Intestinal permeability is a biomarker of intestinal health as it measures the movement of an indigestible marker across the intestinal barrier with excretion in the urine as the primary biological specimen collected for measurement. The adoption of these methods into poultry has been slow due to the lack of urine excretion. Therefore, the objective of this study is to compare differences in intestinal permeability assays in serum of poultry to determine if these assays could be a reliable method to detect changes in intestinal permeability in poultry under a known stressor. To compare the two commonly used methods [fluorescein isothiocyanate-dextran (FITC-D) method and lactulose/mannitol (LMS) dual sugar method], 2 independent trials were conducted with 40 pens split across 2 fed status (fed or fasted for 12 hours) and 4 sugar treatments (no sugar, FITC-D, LMS, FITC-D+LMS). All pens were sampled at 3 timepoints (14, 28, and 42 days of age) with 5 birds sampled per timepoint. Serum FITC-D was determined through fluorescent spectrophotometry, while mannitol and lactulose concentrations were determined using ion chromatography. Data were analyzed using PROC Glimmix. Fed status, sugar treatment, age, and all 2-and 3-way interactions were included as fixed effects. Trial was included in the model as a random effect with pen included as a repeated effect. Serum lactulose and FITC-D increased in fasted compared with fed birds (P < 0.006). Surprisingly, mannitol, which was expected to be similar across fed and fasted, was increased in fed compared with fasted birds (P < 0.001). The increased concentrations of mannitol in fed birds and measurable concentrations of mannitol in birds not given mannitol suggest another molecule eluted at the same rate as mannitol. Therefore, we propose under these conditions that mannitol, and its ratio with lactulose, are not appropriate methods for measuring intestinal permeability in poultry. Lactulose and FITC-D were increased in serum when the birds were provided those sugars and serum concentration of both sugars decreased at 28 days compared with 14 and 42 days (P < 0.003). FITC-D had a significant 2-way interaction for the sugar by fed status (P < 0.05) whereas other 2-and 3-way interactions were similar across treatments (P > 0.202). Serum lactulose concentrations were affected by all 2-and 3-way interactions with elevated serum lactulose concentrations in broilers provided lactulose and fasted (P < 0.001). Birds that did not receive lactulose had very low to undetectable concentrations of lactulose. This reduced background noise for the detection of serum lactulose and the ability statistically to detect small changes in intestinal permeability make lactulose a potential serum biomarker for intestinal permeability in poultry.