Supplementation of a Basal Goat Diet With Incremental Doses of Canola Essential Oil Modulates In Vitro Rumen Fermentation and Microbial Diversity

Abstract

Background: Canola essential oil (CEO) contains linoleic and oleic fatty acids that can inhibit the growth of pathogenic micro-organisms and alter microbial digestion to increase ruminal fermentation and nutrient utilisation.

Objectives: The study evaluated the effect of supplementing a basal goat diet with incremental doses of CEO on chemical constituents and in vitro ruminal fermentation parameters and microbial diversity.

Methods: Experimental treatments were a basal goat diet containing 0.0025% antibiotic growth promoter (AGP) without CEO (POSCON), a basal diet without AGP and CEO (NEGCON), and NEGCON supplemented with 0.5 (CEO5), 1.0 (CEO10), 1.5 (CEO15), and 2.0% (v/w) CEO (CEO20). The treatment samples were homogenised, oven-dried, milled and analysed for chemical constituents. For the in vitro experiment, each sample (1 g) was weighed into serum bottles containing a pre-mixed phosphate buffer solution (pH 6.8) and pre-warmed (39°C) overnight. Ruminal inoculum from three donor goats was used for the incubation. Rumen fermentation parameters and volatile fatty acids were determined and the 16s rRNA gene of the fermentation medium was sequenced and amplified to detect the archaea and bacteria abundance.

Results: Dry matter and organic matter contents were lower (p < 0.05) for CEO15 and CEO20. Crude fat increased with CEO doses with the highest value recorded for CEO20. Treatment CEO20 produced the highest (p < 0.05) value for the immediately fermentable fraction, effective gas production and 96-h partition factor. Lag time had a positive quadratic effect whereas acetic and butyric acids conferred a positive quadratic effect in response to CEO inclusion. A total of 15 phyla, 46 genera and 65 species were identified. The Firmicutes, Bacteroidetes and Actinobacteria predominated the phyla groups while unclassified microbes, Prevotella and Succiniclasticum across all treatments predominated the genera and species. The genus Methanobrevibacter and Ruminococcus reduced significantly at CEO15 and CEO20.

Conclusion: The inclusion of CEO in a basal goat diet increased gas production, partition factor at 96 hour of incubation and decreased total volatile fatty acids. However, 1.5% CEO level enhanced the abundance of fermentative bacteria such as Firmicutes and Actinobacteria while 1.5% and 2% CEO levels reduced the abundance of methanogenic microbes.

Keywords: 16s rRNA; antibiotics; essential oil; microbial abundance; rumen fermentation; volatile fatty acids.