RESUMEN
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.