Effects of preservation conditions of canine feces on in vitro gas production kinetics and fermentation end products

This study investigated the effect of chilling and freezing (for 24 h) canine feces on in vitro gas production kinetics and fermentation end product profiles from carbohydrate-rich (in vitro run 1) and protein-rich (in vitro run 2) substrates. Feces were collected from 3 adult retriever-type dogs fed a canned diet for at least 2 wk. Each fecal sample was divided into 3 portions: 1 portion was used immediately as an inoculum (fresh) and the other 2 portions were used after either chilling to 5 degrees C for 30 min and storage in crushed ice for 23.5 h (chilling) or freezing to -20 degrees C for 30 min and storage in a prefrozen (-20 degrees C) container for 23.5 h (freezing). The medium solution for run 1 contained N whereas that for run 2 was N free. Substrates included fructooligosaccharide (FOS), sugar beet pulp, and wheat middlings in run 1 and soybean meal, poultry meat meal, and feather meal in run 2. Gas production kinetics were calculated from cumulative gas production data measured for 72 h. After incubation, fermentation liquids were analyzed for short-chain fatty acids, NH3, and aromatic compounds. For both in vitro runs, chilling feces did not affect gas production kinetics and end product profiles of substrates compared with inocula from fresh feces. Freezing feces decreased the maximum rate of gas production in phase 2 for FOS (P < 0.001) and across substrates increased gas produced (P <= 0.005) and time of maximum gas production in phase 2 (P < 0.001). Furthermore, compared with fresh fecal inocula, inocula from frozen feces resulted in increased overall indole concentrations in run 1 (P = 0.006) and indole concentrations from soybean meal and poultry meat meal in run 2 (P < 0.001). In run 2, phenol concentrations were greater (P = 0.015) for frozen feces than for fresh feces (P = 0.015). In conclusion, freezing canine feces for 24 h slightly altered fermentative characteristics of fecal inoculum whereas chilling feces in crushed ice for 24 h maintained fermentative characteristics. Chilling feces in crushed ice is a practical method to preserve feces during transport between laboratories within 24 h for in vitro fermentation studies evaluating dietary ingredients.