A low-fiber diet requires a longer adaptation period before collecting feces of pigs compared with a high-fiber diet in digestibility experiments using the inert marker method

The objective was to determine a minimum adaptation period in total tract digestibility experiments using the inert marker method for pigs fed a low- or high-fiber diet. Eight barrows with an initial body weight of 81.5 kg (standard deviation = 5.1) were assigned to 2 dietary treatments in a crossover design. A low-fiber diet was formulated based on ground corn, cornstarch, and soybean meal to contain 50 g/kg amylase-treated neutral detergent fiber. A high-fiber diet was prepared based on ground corn, corn distillers dried grains with solubles, and corn cobs to contain 296 g/kg amylase-treated neutral detergent fiber. In both diets, chromic oxide was included at 5 g/kg as an indigestible inert marker. Daily feed allowance was approximately 2.4% of initial body weight. Equal meals were provided at 0800 and 1700 h. After feeding diets without supplemental chromium (Cr) for 4 days, experimental diets with supplemental Cr were provided to pigs for 8 days. Total fecal collection was conducted during the 8 days with 24-h intervals. Daily Cr concentrations in feces increased linearly and quadratically (P < 0.001) in both low- and high-fiber diet groups as the collection days passed. The break point for fecal Cr concentration in the low-fiber diet group and high-fiber diet group was day 5.46 (SE = 0.145, P < 0.001) and day 3.49 (SE = 0.098, P < 0.001), respectively, based on a one-slope broken-line analysis. Coefficient of apparent total tract digestibility values of energy and nutrients (dry matter, organic matter, and crude protein) on day 3 and day 4 were lower (P < 0.001) than those on day 6 to 8 in the low-fiber diet. In pigs fed the high-fiber diet, the coefficient of apparent total tract digestibility of energy and nutrients on day 3 was lower (P < 0.001) than those on day 4 to 8. In conclusion, the minimum adaption period to achieve a constant inert marker concentration in feces is longer in a low-fiber diet compared with a high-fiber diet. We suggest an adaptation period of at least 6 days before grab sampling of feces when dietary fiber concentration is low.