Effects of a moderate and aggressive implant strategy on the rumen microbial community and metabolome in steers

The effects of growth-promoting implants have been well-defined for their ability to impact growth in beef cattle. Production-relevant microbiomes in the rumen have also been associated with growth traits. However, the role of implant strategies on the rumen microbiome is not understood. The objective was to determine if varying doses of implant hormones cause gain-associated ruminal microbial community shifts. To assess this, a completely randomized design was used and 336 fall-born steers between 450-470 days of age from the germplasm evaluation population at the US Meat Animal Research Center (Clay Center, NE) were divided into two treatment groups: 1) a moderate implant strategy of Revalor-IS (80 mg trenbolone acetate and 16 mg estradiol) followed by Revalor-S (120 mg trenbolone acetate and 24 mg estradiol) and 2) an aggressive implant strategy of Revalor-IS followed by Revalor-200 (200 mg trenbolone acetate and 20 mg estradiol). Steers were fed the same diet (57.0% dry-rolled corn, 30% wet distiller’s grains with solubles, 8.0% alfalfa hay, 4.25% supplement, and 0.75% urea, on a DM basis). Body weights were collected once per month with initial weights of 439.8 ± 43.1 kg. After implants were administered for 84 days, rumen content was collected via orogastric tubing. Samples were sequenced targeting bacterial V1-V3 16S rRNA gene regions, V3-V4 for archaea, and partial 18S rRNA gene of protozoa. Sequences were processed in R utilizing phyloseq with DADA2 and analyzed with DESeq2 to test differential abundances. Untargeted metabolomics was performed on rumen fluid using the UHPLC-HRMS system. Production data between implant strategies was analyzed using a mixed model ANOVA (SASv9.4, Cary, NC) followed by analysis of least square means. Alpha- and beta-diversity between strategies did not differ for bacteria, archaea, or protozoa (P > 0.05). Average daily gain was different (P = 0.01; 1.72 vs 1.66 ± 0.02 kg, aggressive vs moderate, respectively); however, large microbial community shifts were not associated implant strategy. Two metabolites, acetyllysine and N-acetylornithine, were significant between implant strategy (P ≤ 0.04). Understanding associations between the rumen microbiome and implant strategies may allow improvement of growth in beef cattle.