Effects of Plant Extracts on Amino Acid Metabolism in Pig Small-Intestinal Bacteria in Vitro

As alternatives to feed antibiotics, plant extracts have been used in animal husbandry for many years to improve animal health and growth. However, the underlying mechanisms remain largely unknown. Recent studies showed the important role of bacteria in amino acid (AA) metabolism in the pig small intestine. We hypothesized that the beneficial effect of plant extracts may result, in part, from their regulatory role in AA catabolism by small-intestinal bacteria. Three plant extracts, cinnamaldehyde, thymol, and anethol, were incubated with pig small-intestinal bacteria. Ileal digesta collected from the ileal cannula of four 20 kg ± 5 kg Duroc x Landrace x Large white pigs were mixed, processed and inoculated into the chemically defined media (including mixtures of AA). Concentrations of the plant extracts in the media were 0 (control), 25 , 50 or 100 umol/L. Incubation was carried out for 24 h at 37 °C, and samples were taken at different time points for the determination of ammonia-nitrogen (NH₃-N), AA and polyamines. At the end of the 24-h culture, the addition of thymol, cinnamaldehyde or anethol at concentration of 100 umol/L reduced (P ≤ 0.05) ammonia production by 16 %, 22 %, and 42 %, respectively. Compared to the control, 50 and 100 umol/L thymol, cinnamaldehyde or anethol reduced (P ≤ 0.05) the bacterial utilization of aspartate, glutamine, histidine, tyrosine and tryptophan over a 12-h period of incubation. In addition, 50 and 100 umol/L thymol or cinnamaldehyde reduced the 12-h bacterial utilization of glycine, and similar observations were observed with anethol after a 24-h period of incubation. Putrescine concentration increased (P ≤ 0.05) in the media with 50 and 100 umol/L thymol after a 12-h period of incubation. Likewise, cadaverine concentration increased (P≤ 0.05) in the media with 50 and 100 umol/L thymol or cinnamaldehyde. Collectively, these observations indicate that thymol, cinnamaldehyde or anethol can inhibit AA degradation in pig small-intestinal bacteria, and the essential oils sever as good alternatives to antibiotics for improving AA nutrition, growth and health in pigs.

Works in the laboratory were supported by the National Key Basic Research Program of China (2013CB127303), Natural Science Foundation of China (31301979). The authors also thank Ms. Yan Lei (Dadhank Biotech Corp) for support. Corresponding author: daizhaolai@cau.edu.cn.