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

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.

Beta-Adrenergic Agonists, Dietary Protein, and Rumen Bacterial Community Interactions in Beef Cattle: A Review.

Improving beef production efficiency, sustainability, and food security is crucial for meeting the growing global demand for beef while minimizing environmental impact, conserving resources, ensuring economic viability, and promoting animal welfare. Beta-adrenergic agonists and dietary protein have been critical factors in beef cattle production. Beta-agonists enhance growth, improve feed efficiency, and influence carcass composition, while dietary protein provides the necessary nutrients for muscle development and overall health. A balanced approach to their use and incorporation into cattle diets can lead to more efficient and sustainable beef production. However, microbiome technologies play an increasingly important role in beef cattle production, particularly by optimizing rumen fermentation, enhancing nutrient utilization, supporting gut health, and enhancing feed efficiency. Therefore, optimizing rumen fermentation, diet, and growth-promoting technologies has the potential to increase energy capture and improve performance. This review addresses the interactions among beta-adrenergic agonists, protein level and source, and the ruminal microbiome. By adopting innovative technologies, sustainable practices, and responsible management strategies, the beef industry can contribute to a more secure and sustainable food future. Continued research and development in this field can lead to innovative solutions that benefit both producers and the environment.

Rumen Biogeographical Regions and Microbiome Variation.

The rumen is a complex organ that is critical for its host to convert low-quality feedstuffs into energy. The conversion of lignocellulosic biomass to volatile fatty acids and other end products is primarily driven by the rumen microbiome and its interaction with the host. Importantly, the rumen is demarcated into five distinct rumen sacs as a result of anatomical structure, resulting in variable physiology among the sacs. However, rumen nutritional and microbiome studies have historically focused on the bulk content or fluids sampled from single regions within the rumen. Examining the rumen microbiome from only one or two biogeographical regions is likely not sufficient to provide a comprehensive analysis of the rumen microbiome and its fermentative capacity. Rumen biogeography, digesta fraction, and microbial rumen-tissue association all impact the diversity and function of the entirety of the rumen microbiome. Therefore, this review discusses the importance of the rumen biographical regions and their contribution to microbiome variation.

Effects of grazing different ergovaline concentrations on vasoactivity of bovine lateral saphenous vein.

Previous research has demonstrated that exposure to ergot alkaloids reduces vasoactivity of serotonin (5HT) receptors. Chemical suppression of tall fescue seedhead production is a tool to reduce the level of exposure to ergot alkaloids by a grazing animal. Therefore, the objective was to evaluate contractility of lateral saphenous veins biopsied from mixed breed steers following a 87- to 101-d grazing period on 3-ha pastures of bermudagrass (Cynodon dactylon; n = 5 steers; BW = 340 ± 9 kg), or toxic endophyte-infected tall fescue (Lolium arundinaceum) that was not treated (n = 5 steers; BW = 300 ± 6; 0.56 ppm ergovaline) or was treated (n = 5 steers; BW = 294 ± 9 kg; 0.24 ppm ergovaline) with herbicide containing aminopyralid and metsulfuron-methyl. To evaluate contractility, biopsied veins were mounted in a multimyograph and exposed to increasing concentrations of a tall fescue seed extract (EXT; ergovaline source) and 5HT1B (CP 93129), 5HT1D (L-694,247), and 5HT2A (TCB2) agonists. All contractility data were normalized to a maximal response of 1 × 10-4 M norepinephrine and were analyzed as a split plot treatment design using SAS for effects of pasture treatment, agonist concentration, and the interaction. There was no contractile response to any concentration of 5HT1B agonist in any of the pasture treatments. There were pasture × concentration interactions for contractile responses to 5HT2A agonist (P < 0.01) and EXT (P < 0.01). For both EXT and TCB2, veins from bermudagrass steers were more vasoactive to the higher concentrations of these compounds (P < 0.05), and there were no differences between veins collected from the unsuppressed or seedhead-suppressed treatments (P = 0.66). There was also a pasture × concentration interaction for the contractile responses to 5HT1D agonist (P < 0.01). However, these responses were not sigmoidal and reached a zenith at 5 × 10-7 and 1 × 10-6 M. At these concentrations, the response was greatest for veins from the unsuppressed treatment (P < 0.05) and did not differ between veins from suppressed and bermudagrass treatments (P = 0.41). Although reduced levels of ergovaline in seedhead-suppressed pastures did not alter vasoactivity of 5HT2A or 5HT1B receptors in the lateral saphenous vein, elevated vasoactivity of 5HT1D in veins from unsuppressed tall fescue pasture treatment suggests that lower ergovaline levels in seedhead-suppressed pastures can influence the vascular effects of ergot alkaloids.