Effects of commercial aldehydes from green leaf volatiles (green odour) on rumen microbial population and fermentation profile in an artificial rumen (Rusitec).

The effects of plant metabolites on rumen metabolism vary greatly depending on their antimicrobial spectrum and applied doses. In this study, the minimum inhibitory concentrations (MICs) of commercial aldehydes, trans-2-hexenal (T2H), cis-3-hexenal (C3H), trans-2-nonenal (T2N), and trans-2-decenal (T2D) from green leaf volatiles, were tested on rumen bacteria. These compounds were found more effective on Gram-positive rumen bacteria than the Gram-negatives, and C3H was the most effective compound. Then, for 14 days, the in vitro effects of C3H compared with monensin (5 mg/day) on the rumen microbial population and ruminal fermentation at 187.5, 375 and 750 mg/day doses were tested based on the MIC value (500 µg/mL) by using the rumen simulation technique (Rusitec). Supplementation with C3H at 375 mg/day increased the cell numbers of Butyrivibrio fibrisolvens significantly. The addition of C3H at 375 and 750 mg/day doses also increased Streptecoccus bovis cell counts. The use of monensin did not affect the cell numbers of these bacteria. On the other hand, C3H did not change the counts of total bacteria, methanogens, or hyper-ammonia-producing (HAP) bacteria like monensin. The numbers of Ruminococcus albus and Ruminococcus flavefaciens were also stable in the presence of C3H but decreased significantly with the addition of monensin (P < 0.05). Fibrobacter succinogenes, Megasphaera elsdenii, and Selenomonas ruminantium cell counts were not affected by either application. In addition, C3H increased the acetate and methane production along with the acetate-to-propionate ratio at all tested concentrations, unlike monensin. Supplementation with C3H decreased propionate production significantly, except at the 187.5 mg/day dose. Butyrate production increased (P < 0.05) only in the presence of 187.5 and 375 mg/day doses of C3H. Production of total volatile fatty acids (VFA) and dry matter digestibility (DMD) did not change in treatment groups. Also, the total protozoa numbers and ammonia-N concentrations significantly decreased (P < 0.05) in C3H-treated samples, similar to monensin. Although C3H did not have favorable effects on energy efficiency, it suppressed rumen protozoa and mitigated rumen ammonia without adversely effecting ruminal fermentation in all applied doses. Based on the result, C3H has the potential to improve protein utilization in the rumen.