The Effect of Adding Thymol on Rumen Fermentations, the Digestibility of Nutrients and Bacterial Count of Arabi Lamb’s Rumen Fluid in Vitro

Abstract

This study aimed to investigate the microbial responses to thymol supplementation in the rumen fluid of Arabi lambs and determine the effective dose of thymol on rumen fermentation. Thymol was added at different concentrations (0, 200, 300, 400 mg thymol/L of rumen fluid) with four replicates for each treatment during a 24-hour laboratory incubation period. The Real-Time PCR-DNA technique was used to count the bacteria in the rumen fluid, and the fermentations of the rumen fluid were examined. The results indicated that thymol did not have an effect on the pH and ammonia nitrogen concentration of the rumen fluid. However, the addition of thymol at concentrations of 200, 300, and 400 mg/L showed significant improvements in metabolic energy, total fatty acids, and total gas production compared to the control treatment (0 mg thymol). Methane gas concentration significantly decreased when thymol was added at a concentration of 400 mg/L. The digestibility of organic matter and fiber improved at concentrations of 300 and 400 mg/L, respectively. The digestibility of crude protein was significantly higher (P<0.05) in the control and 200 mg/L treatments compared to the 300 and 400 mg/L treatments. Regarding the number of bacteria, there were no significant differences between the treatments in the average total number of bacteria and the number of fiber-degrading bacteria of the genus Ruminococcus flavefaciens in the rumen fluid. However, the addition of thymol led to a significant increase in the number of fibrous bacteria from the genus Ruminococcus albus. The third treatment (300 mg/L) showed the highest number of Ruminococcus albus bacteria (5.86 × 710 CFU/mL rumen fluid) compared to the first and second treatments (4.55 × 710, 4.71 × 710 CFU/mL rumen fluid, respectively). In conclusion, thymol improved metabolic energy, total fatty acids, digestibility of organic matter and total gas production, while reducing methane gas concentration. The addition of thymol did not significantly affect the total number of bacteria but increased the number of fibrous bacteria from the genus Ruminococcus albus.