Diet and measurement techniques affect small intestinal digesta viscosity among dogs

Because increasing viscosity of gastrointestinal tract contents has been shown to alter physiologic responses in many species, and no single standardized method of intestinal viscosity measurement exists, effects of diet and measurement techniques were studied in a canine model. Three experiments were conducted to evaluate the use of mixer viscometry, effects of freezing, centrifugation, time of sampling, and dilution of digesta, and effects of diet on viscosity of canine ileal digesta and simulated small intestinal digesta viscosity. Digesta viscosity values measured at 21°C were within 5% of those at 21°C after a 24-hour freeze. Viscosity constants of whole digesta sampled between 8:00 am and 2:00 pm daily ranged from 6575 to 32 692 mPa · s and 7.47 to 9.03 mPa · s after centrifugation. Digesta sampled between 2:00 pm and 8:00 pm daily had viscosity constants of whole digesta ranging from 7137 to 17 345 mPa · s and 6.42 and 9.46 mPa · s after centrifugation. Digesta samples diluted with Millipore filtered water, to determine whether a dilution factor could be used to estimate viscosity, had drastically underestimated viscosity constants. Ileal digesta viscosity constants were similar for dogs fed test diets varying in carbohydrate source and ranged from 6901 to 12 590 mPa · s. During simulated small intestinal simulation, viscosity peaked between 6 and 9 hours. Data indicate that alteration of digesta by centrifugation or dilution underestimates viscosity data. Viscosity of whole digesta can be measured using mixer viscometry. Variations in diet ingredients appear to alter intestinal digesta viscosity, indicating further need for investigation of the role of diet in viscosity.