Heat stress increases gut permeability in pigs– application of a non-invasive assay

Heat stress plays an important role in livestock animals. Several studies already described increased gut permeability in pigs during heat stress using invasive technologies e.g., Ussing Chamber. In human studies non-invasive sugar tests are quite often used to measure gut barrier function. We therefore evaluated the influence of heat stress on gut permeability of pigs with the dual sugar assay. Eight pigs were placed into metabolic cages (two pigs per cage) at D35 after weaning. Pigs were allowed to adapt to the cages for 4 d. At d 0 of the trial period pigs were kept at thermoneutral conditions (32°C, 24 h) and on d 1,2 and 3 pigs were exposed to heat stress conditions (6 h 35°C, 18 h 32°C). At d 0 and 2 the dual sugar permeability assay was performed. Therefore, agar containing lactulose (500 mg/kg body weight) and rhamnose (100 mg/kg body weight) was fed to the pigs. Urine was sampled 2, 4, and 6 h after sugar intake. Urine samples were frozen at- 20°C and lactulose and rhamnose concentrations were determined via HPLC-MS/MS. All data obtained in the experiment were analyzed with a nonparametric test. There was no significant difference between the cumulative rhamnose and lactulose excretion between d 0 (2.1%; 0.52%) and d 2 (1.2%; 0.84%). However, the lactulose rhamnose excretion ratio was significantly increased (p = 0.0286) of pigs under heat stress conditions (0.66) compared with thermoneutral conditions (0.24). Our study showed that the dual sugar assay can be used to evaluate gut permeability with a non-invasive method. We furthermore could once more highlight the negative impact heat stress can have on the welfare and health of pigs.