Feeding an Essential Oils Blend to Neonatal Holstein Dairy Calves Increased Rumen Propionate Concentration and Resulted in Higher Representation of a Previously Uncharacterized Strain of Prevotella Ruminicola

Antibiotics are extensively used in dairy production to increase immunity, reduce stress and susceptibility to pathogens, as well as stimulate growth in neonatal calves. Antibiotic use in animal production has become a public health concern, and essential oils (EO) have been proposed as a viable alternative. To evaluate the effects of feeding a commercial blend of EO (carvacrol, caryophyllene, p-cymene, cineole, terpinene, and thymol) and prebiotics (arabinogalactans) (Stay Strong; Ralco, Inc., Marshall, MN) on the rumen microbiota of neonatal weaned Holstein dairy calves, 20 calves blocked by age were randomly assigned to either a milk replacer (MR) (24:20% CP: fat; as-fed basis) supplemented with EO (3.75 g/feeding) or MR without supplementation. Treatment and control MR were fed at a rate of 0.40 kg/calf twice daily until d 35, then reduced to once daily at d 36 to facilitate weaning. Pelleted calf starter (20% CP) and water were provided ad libitum. Rumen samples were collected by stomach tubing one day after weaning for bacteria composition and volatile fatty acid (VFA) analyses. Amplicon sequencing was carried out targeting the V1 - V3 region of the 16S rRNA gene, which generated a total of 347,254 high quality, non-chimeric reads, ranging from 1,803 to 69,842 reads per sample. Twenty six species-level Operational Taxonomic Unit (OTUs) with a relative abundance at least 1% were found across all samples. Only one OTU, corresponding to a previously uncharacterized strain of Prevotella ruminicola, showed higher (17.84 % ± 14.80 %) relative abundance (P < 0.05) in calves fed EO compared to control (2.34 % ± 4.62%). The VFA analysis showed higher concentration of propionate (P< 0.05) with EO fed calves (40.25 mM ± 9.09 mM) compared to control fed calves (31.05 mM ± 9.42 mM), whereas, there was no difference in total VFA and other VFAs (acetate, butyrate, isobutyrate, valerate, and isovalerate) concentrations . Together, these results suggest that EO supplementation can modulate rumen microbiome and VFA composition during rumen development of dairy calves.