Effects of protein concentration and beta-adrenergic agonists on ruminal bacterial communities in finishing beef heifers

Authors: PFAU, ALISON - University Of Tennessee; HENNIGER, MADISON - University Of Tennessee; SAMUELSON, KENDALL - Texas A&M University; HALES, KRISTIN - Texas Tech University; LOEST, CLINT - New Mexico State University; HUBBERT, MIKE - Clayton Livestock Research Center; Lindholm-Perry, Amanda; EGERT-MCLEAN, AMANDA - University Of Tennessee; MASON, KATIE - University Of Tennessee; SHEPHERD, ELIZABETH - University Of Tennessee; VOY, BRYNN - University Of Tennessee; MYER, PHILLIP - University Of Tennessee

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2023
Publication Date: 2/29/2024
Citation: Pfau, A.P., Henniger, M.T., Samuelson, K.L., Hales, K.E., Loest, C.A., Hubbert, M.E., Lindholm-Perry, A.K., Egert-McLean, A.M., Mason, K., Shepherd, E.A., Voy, B.H., Myer, P.R. 2024. Effects of protein concentration and beta-adrenergic agonists on ruminal bacterial communities in finishing beef heifers. PLOS ONE. 19(2). Article e0296407. https://doi.org/10.1371/journal.pone.0296407.
DOI: https://doi.org/10.1371/journal.pone.0296407

Interpretive Summary: Growth promoting products are commonly used by producers to improve cattle growth. However, increasing growth also requires providing a sufficient amount of protein to allow rumen microbes to digest feed and allow for its conversion to nutrients for the animal. Microbes use rumen degradable protein for their growth, but rumen undegradable protein escapes digestion by the microbes and is available for direct use by the animal. There is little research evaluating the effect of growth promoters and protein type on the rumen microbial communities. To evaluate the effect of protein type and growth promoters, heifers were fed three different protein types with and without growth promoters. Rumen bacterial populations differed among animals fed different types of protein indicating that various proteins in the diet have a possible effect on the microbial communities present in the rumen, whereas growth promoters had limited effect on the microbes present.

Technical Abstract: To improve animal performance and modify growth by increasing lean tissue accretion, beef cattle production has relied on use of growth promoting technologies such as beta-adrenergic agonists. These synthetic catecholamines, combined with the variable inclusion of rumen degradable (RDP) and undegradable protein (RUP), improve feed efficiency and rate of gain in finishing beef cattle. However, research regarding the impact of beta-adrenergic agonists, protein level, and source on the ruminal microbiome is limited. The objective of this study was to determine the effect of different protein concentrations and beta-adrenergic agonist (ractopamine hydrochloride; RAC) on ruminal bacterial communities in finishing beef heifers. Heifers (n=140) were ranked according to body weight and assigned to pens in a generalized complete block design with a 3 × 2 factorial arrangement of treatments of 6 different treatment combinations, containing 3 protein treatments (Control: 13.9% CP, 8.9% RDP, and 5.0% RUP; High RDP: 20.9% CP, 14.4% RDP, 6.5% RUP; or High RUP: 20.9% CP, 9.7% RDP, 11.2% RUP) and 2 RAC treatments (0 and 400 mg/day). Rumen samples were collected via orogastric tubing 7 days before harvest. DNA from rumen samples were sequenced to identify bacteria based on the V1-V3 hypervariable regions of the 16S rRNA gene. Reads from treatments were analyzed using the packages ‘phyloseq’ and ‘dada2’ within the R environment. Beta diversity was analyzed based on Bray-Curtis distances and was significantly different among protein and RAC treatments (P < 0.05). Alpha diversity metrics, such as Chao1 and Shannon diversity indices, were not significantly different (P > 0.05). Bacterial differences among treatments after analyses using PROC MIXED in SAS 9 were identified for the main effects of protein concentration (P < 0.05), rather than their interaction. These results suggest possible effects on microbial communities with different concentrations of protein but limited impact with RAC. However, both may potentially act synergistically to improve performance in finishing beef cattle.