Three-step in vitro digestion model for evaluating and predicting fecal odor emission from growing pigs with different dietary protein intakes.

OBJECTIVE: The objective of this study was to select an effective in vitro digestion-fermentation model to estimate the effect of decreasing dietary crude protein (CP) on odor emission during pig production and to suggest potential prediction markers through in vitro and in vivo experiments. METHODS: In the in vitro experiment, three diet formulations with different CP contents (170 g/kg, 150 g/kg, and 130 g/kg) but containing the same standardized ileal digestible essential amino acids (SID-EAA) were assessed. Each diet was evaluated by two different in vitro gastric-intestinal phase digestion methods (flask and dialysis), combined with fresh pig feces-ferment inoculation. Eighteen growing barrows (31.9±1.6 kg) were divided into three groups: control diet (180 g CP/kg, without SID-EAA adjustment), 170 g CP/kg diet, and 150 g CP/kg diet for 4 weeks. RESULTS: The in vitro digestion results indicated that in vitro digestibility was affected by the gastric-intestinal phase digestion method and dietary CP level. According to the gas kinetic and digestibility results, the dialysis method showed greater distinguishability for dietary CP level adjustment. Nitrogen-related odor compounds (NH3-N, indole, p-cresol, and skatole) were highly correlated with urease and protease activity. The feeding study indicated that both EAA-adjusted diets resulted in a lower odor emission especially in p-cresol and skatole. Both protease and urease activity in feces were also closely related to odor emissions from nitrogen metabolism compounds. CONCLUSION: Dialysis digestion in the gastric-intestinal phase followed by fresh fecal inoculation fermentation is suitable for in vitro diet evaluation. The enzyme activity in the fermentation and the fecal samples might provide a simple and effective estimation tool for nitrogen-related odor emission prediction in both in vitro and in vivo experiments.

Effects of essential oil mixtures on nitrogen metabolism and odor emission via in vitro simulated digestion and in vivo growing pig experiments.

BACKGROUND: Essential oils (EOs) are extensively used in swine production because of their bioactive action in gut health. In addition, some EOs have the potential to reduce waste emission. The present study aimed to find an optimal combination of carvacrol, thymol and cinnamaldehyde to promote nitrogen utilization and reduce waste emission by a model in vitro and an animal study. RESULTS: In the study in vitro, various dosages of essential oils (EOs) were used to evaluate the effect on nitrogen metabolism through a three-step model. Compared with other EO combinations, 2EO (10 ppm cinnamaldehyde and 20 ppm thymol), and 3EO (10 ppm cinnamaldehyde, 20 ppm thymol and 200 ppm carvacrol) displayed greater nitrogen digestibility, lesser ammonia production and lower activity of microbial enzymes. In the animal study, growing male Landrace × Yorkshire pigs (initial body weight: 31.8 ± 3.3 kg, n = 18) were randomly divided into three groups and fed the control, 2EO or 3EO diet for 4 weeks. Pigs fed 3EO exhibited the greatest nitrogen digestibility (85.4%, P < 0.05). EO supplementation decreased the emission of ammonia (130-140 vs. 223 mg g-1 ) and total fecal nitrogen (8.0-9.9 vs. 12.4 g d-1 ) (P < 0.05). Microbial protease and urease activities were inhibited by EO treatments (P < 0.01). Both 2EO and 3EO reduced the content of indole and 3-methylindole (P < 0.01), whereas only 2EO caused a decrease in p-cresol (P < 0.1). CONCLUSION: 2EO was suitable for reducing waste emission and odorous compounds in growing pigs, whereas 3EO was optimal for increasing nitrogen utilization and partially reducing waste odorous compounds. © 2021 Society of Chemical Industry.