In an earlier article, I discussed how the beef industry might be able to reduce the impact of bovine respiratory disease (BRD) by utilizing Hazard Analysis Critical Control Points principles and practices. Here, we’ll take a look at how that might look in practice.
Background
The BRD bacterial species preexist in the upper respiratory tract of healthy calves. Current understanding suggests that BRD occurs when the microbiome and virome are perturbed by a transient stressful event, which suppresses the immune system. Then, the viruses replicate, damage occurs to the natural defense mechanisms of the respiratory tract, and bacteria invade the lower respiratory tract, causing infection. The challenge is to identify and quantify the factors that account for the immunosuppression. This is easier said than done, since knowledge of biomarkers for quantification of stress is incomplete and chuteside implementation is not yet possible.
Hazards
Metaphylaxis has been the answer. Metaphylaxis is the administration of antimicrobials, often preemptively, to a cohort of feeder cattle judged to be at high risk for BRD. Injectable products have been shown to be more effective than oral products. Yet while this is an effective strategy, antimicrobial resistance by BRD pathogenic bacterial species occurs.
One must accept the presence of BRD bacterial species and viruses in or on feeder cattle. Viruses associated with BRD exist in the respiratory tract of cattle upon feedlot arrival, but a University of Saskatchewan study found in 2021 that BRD subsequently occurred in only 50% of the sampled crossbred heifer, steer and bull beef calves (average 570 pounds).
Nevertheless, there is a kind of bacterial transference that is to be avoided. It is the cross-contamination involving BRD pathogenic bacterial strains that harbor the genes for antimicrobial resistance. These genes emerge in response to repeated exposure to antibiotics and, once present, multiply as a component of BRD bacterial growth. The concerning knowledge is that this antimicrobial resistance persists in BRD bacteria even after there is no longer exposure to the causative antibiotic. Any practice that would impede development of antimicrobial resistance in BRD bacteria, or any intervention that would impede transfer of these organisms from a surface or harborage site onto calves would qualify as a critical control point.
A collaborative project between Agriculture and Agri-Food Canada and University of Saskatchewan found that bacterial strains associated with BRD and possessing AMR were isolated more often from dairy-type than from beef-type cattle in Canadian feedlots. Also, beef-type cattle from backgrounding operations presented higher odds of antimicrobial bacterial cultures as compared to auction-derived calves. Since high levels of resistance to tetracycline and macrolide (e.g., tilmicosin, tulathromycin and tylosin) antibiotics are prevalent in Alberta, the response has been to recommend a surveillance program for antimicrobial resistance for the purpose of enabling judicial choices in antimicrobial use going forward. While surveillance results would be informative, this does not solve the challenge posed by further development of antimicrobial resistance.
Here, a HACCP approach is suggested for the purpose of bringing even more information to bear on the judicial use of antibiotics, with the aim of further slowing the pace of AMR development. While it is not publicly known whether new antimicrobial products are in development, it is probable that bacterial species will eventually develop resistance to them, too. To preserve the effectiveness of existing and future antimicrobials, it seems prudent to exercise control over BRD pathogens by implementing additional critical control points.
Corrective actions
Some studies have addressed sanitation in the context of BRD control, especially for receiving and hospital pens, feedbunks and water troughs, and avoiding crossover between equipment use for feed versus manure handling. However, in looking at the literature, you would be hard pressed to find cattle processing equipment mentioned. It has been suggested that bacterial biofilms in the feedyard environment might be a harborage site for strains having AMR.
Returning to the E. coli O157 challenge faced by the beef industry, this bacterial strain which is present on cattle hides is a significant risk factor leading to carcass contamination. A 2008 study of Scottish cattle studied transference of E. coli O157 to the brisket from sources other than the animal itself, its farm of origin or herdmates. Commercial transport to harvest was identified as a pre-harvest risk factor. Do the hides of calves pick up BRD pathogens from contact surfaces? Is licking behavior of calves involved in pathogen transfer?
In recent years, I toured a multinational sanitation company and viewed their displays of environments in which their chemistries have been applied. One such display was of a hospital surgery room. Of course, a surgery room would be sanitized between patients. Upon reflection, cattle processing facilities came to mind, with groups of cattle going through the same alley and squeeze chute. They each spend very little time there, but they do have contact with surfaces touched by many predecessors.
One has to wonder if sanitation for a cattle processing facility has been evaluated as a critical control point. If these facilities are under roof, there is no opportunity for UV rays to exercise their cleansing effect. I have observed a few processing areas that were designed for and were washed down (disinfected?) at the end of the day. Could the processing equipment and surrounding facilities be a site for cross-contamination between cohorts of cattle? Is there merit in implementing sanitary design principles into remodeling or design of cattle processing facilities?
Has anyone conducted a metagenomic profiling of cattle processing facilities in auction barns, background yards and feedyards, as has been done for meat plants? Would genes for antimicrobial resistance be found in a cattle processing facility? If so, how would one envision alley and squeeze chute sanitization to be done in an efficient and effective manner? The Beef Quality Assurance manual includes tables that display descriptive characteristics of cattle viruses as well as characteristics of disinfectants.
Another tactic could involve maternal bovine appeasing substance (mBAS), which is a proprietary mixture of fatty acids. A recent Texas A&M University study administered mBAS to high-risk Angus-influenced bull calves averaging 440 pounds upon arrival at the feedlot and prior to processing. The purpose of topical application of mBAS was to reduce stress in these calves. Following castration, serum cortisol concentration, an indicator of stress, was reduced by mBAS treatment. The mBAS did not affect BRD incidence or calf growth, but return to health after BRD treatment was better for mBAS-treated calves and mBAS reduced BRD deaths from 10% to 1.66%. Also, medication costs were not affected by mBAS versus control, but the return on investment was huge for mBAS because of reduced death loss.
To reduce the incidence of BRD and to preserve efficacy of the antimicrobial approach, additional tactics will be needed. Novel thinking based on the available science that describes the development of BRD will be rewarded.
Summary
If one incorporated a sanitation program into an auction barn and/or feedyard operation, would it decrease pathogen load or pathogen transfer? Administration of mBAS seems to enable the immune system to tolerate stressors during on-arrival calf processing. It’s certainly a line of thought worth exploring.
References omitted but are available upon request by sending an email to the editor.
