IntroductionThe objectives of this study were to evaluate the impacts of two modified-live virus (MLV) vaccination protocols and respiratory disease (BRD) occurrence on the microbial community composition of the nasopharynx in feedlot cattle.MethodsThe treatment groups included in this randomized controlled trial included: 1) no viral respiratory vaccination (CON), 2) intranasal, trivalent, MLV respiratory vaccine in addition to a parenteral BVDV type I and II vaccine (INT), and 3) parenteral, pentavalent, MLV respiratory vaccination against the same agents (INJ). Calves (n = 525) arrived in 5 truckload blocks and were stratified by body weight, sex, and presence of a pre-existing identification ear-tag. A total of 600 nasal swab samples were selected for DNA extraction and subsequent 16S rRNA gene sequencing to characterize the microbiome of the upper respiratory tract. Nasal swabs collected on d 28 from healthy cattle were used to evaluate the impact of vaccination on upper respiratory tract (URT) microbial communities.ResultsFirmicutes were less abundant in INT calves (n = 114; P < 0.05) and this difference was attributed to decreased relative abundance (RA) of Mycoplasma spp. (P = 0.04). Mannheimia and Pasteurella had lower RA in INT (P < 0.05). The microbiome in healthy animals on d 28 had increased Proteobacteria (largely Moraxella spp.) and decreased Firmicutes (comprised almost exclusively of Mycoplasma spp.) compared to animals that were treated for or died from BRD (P < 0.05). Cattle that died had a greater RA of Mycoplasma spp. in their respiratory microbiome on d 0 (P < 0.02). Richness was similar on d 0 and 28, but diversity increased for all animals on d 28 (P>0.05).
The objectives were to evaluate the effects of metaphylaxis (META) and pull-and-treat (PT) programs on health, antimicrobial use, beef production, economics, and greenhouse gas emissions in cattle at medium risk for bovine respiratory disease (BRD). A randomized complete block design was used at two US commercial feedlots. Steers and heifers [2366 total; 261 (±11.0) kg initial weight] were blocked by sex and feedlot arrival, and allocated to one of two pens within a block (16 pens total, eight blocks). Pens were randomly assigned to treatment: META, tulathromycin injection at initial processing; or PT, tulathromycin injection only for first clinical BRD treatment. Data were analyzed with linear and generalized linear mixed models. There was greater BRD morbidity in PT than META cattle (17.2% vs. 7.3% respectively; p < 0.01), and greater total mortality (2.5% vs. 1.1% respectively; p = 0.03). Per animal enrolled, 1.1 antimicrobial doses were used for META compared to 0.2 for PT (p < 0.01). Per animal enrolled, final live (p = 0.04) and carcass (p = 0.08) weights were greater for META than PT; however, net returns ($/animal) were not significantly different (p = 0.71). Compared to PT, total lifetime estimated CO2 equivalent emissions from production were reduced by 2% per unit of live weight for META (p = 0.09). While antimicrobial use was reduced with PT, there may be substantial negative impacts on other outcomes if META was not used in this type of cattle population.
Mycoplasma bovis is a bacterium member of the family Mycoplasmataceae, characterized by a small genome, lack of cell wall, and high nutritional requirements for in vitro growth (Li et al., 2011; Parker et al., 2018; Dudek et al., 2020). Traditionally, M. bovis has been linked to chronic BRD cases and treatment failures (Booker et al., 2008; Hermeyer et al., 2012; Gershwin et al., 2015; Becker et al., 2020). Several virulence factors have been implicated in M. bovis ability to persist in the lungs of cattle with BRD, such as variable surface proteins (Vsp), adhesins, nucleases, H2O2 production and biofilm formation (Burki et al., 2015; Perez-Casal, 2020). Due to the difficulties of growing M. bovis in the lab, the inherent culture bias (Prakash et al., 2021) could have shaped our current knowledge of M. bovis in BRD. Recent evidence has emerged linking M. bovis presence in the upper respiratory tract with acute BRD status (Timsit et al., 2018; Centeno-Martinez et al., 2022). However, the association between M. bovis and other BRD agents, especially Mannheimia haemolytica, over time remains unknown during the first month on the feedlot. A more comprehensive understanding of the dependencies among BRD pathogens over time will help develop new non-antibiotic control strategies and subsequently reduce the burden of BRD on beef cattle production. Therefore, this study aimed to evaluate the association of M. bovis and M. haemolytica during acute BRD in feedlot cattle.
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