PSII-26 Effect of fennel essential oils at different particle sizes and inclusion levels on volatile fatty acid production in an in vitro rumen fermentation system.

Abstract This study aimed to evaluate the effects of fennel essential oils at two particle sizes (normal and nano) and three levels (10, 20, and 30 µL/g of substrate) on total and individual volatile fatty acid (VFA) production in an in vitro batch culture system. The experiment followed a 2 × 3 + 1 factorial design, with fennel essential oils incorporated into a substrate mixture of corn silage (64.35%), alfalfa (3.48%), and concentrate (32.17%). The rumen liquor was collected from four mature cannulated Holstein Friesian cows and incubated for 48 h, with VFAs analyzed at 48 h using gas chromatography-mass spectrometry (GC/MS). Data analysis was done using SAS Studio, while Tukey’s mean separation at 5% significance level indicated no significant trends in VFA production associated with particle size or oil inclusion level. The results revealed that neither particle size nor inclusion level significantly (P >0.05) affected VFA concentrations, including acetate, propionate, butyrate, iso-butyric acid, iso-valerate, and valerate at 48 h of incubation. Specifically, for VFA, no significant linear or quadratic trends were observed for either particle size condition. Acetate concentrations also showed no significant differences across levels or particle sizes. Similarly, Propionate did not exhibit any significant trend for particle size or level. No significant effects were observed for iso-butyric acid, butyrate, iso-valerate, valerate, or acetate-propionate ratio. These findings suggest that neither particle size nor level significantly influences VFA production at 48 h under the conditions tested. It is concluded that the inclusion of fennel essential oils at varying particle sizes and levels, under the tested conditions, had minimal effects on ruminal fermentation and VFA profiles in Holstein Friesian cows. Further studies may be needed to explore different dosages.