**2.2 Current prevention and control strategies for BRD in feedlots**

Prevention and control of BRD in large commercial feedlots in North America are aimed mainly at bacterial pathogens, through the use of antimicrobials and vaccination programs. Cattle considered at high risk for the development of BRD are often given metaphylactic antimicrobials upon feedlot arrival [26]. Metaphylaxis

**21**

*Bovine Respiratory Disease in Feedlot Cattle: Antimicrobial Resistance in Bovine Respiratory…*

is defined as the mass treatment of an entire group or population of cattle with an antimicrobial to prevent and minimize an expected outbreak of disease [26]. Overall, 59.3% of feedlots in the USA with a capacity of >1000 head cattle use injective metaphylaxis, with approximately 21.3% of the cattle placed in the feedlot, receive metaphylactic antibiotics [6]. In Western Canada, more than 80% of the cattle in some feedlots receive injectable metaphylactic antibiotics on arrival to the feedlot (Personal communication with Dr. Steve Hendrick, Coaldale Vet Clinic, Alberta, Canada). The decision for metaphylactic intervention is primarily based on the nature of cattle population arriving at the feedlot. Cattle populations that are lighter body weight, multiple sources origin, and have poor health history and experienced long distance travel are often subjected to metaphylactic treatment at feedlot entry [26]. Metaphylactic treatment reduces BRD-associated morbidity and mortality by eradicating the already existing bacterial infections and preventing colonization and proliferation of pathogens in those immunosuppressed and vulnerable animals. Although efficacy of metaphylaxis to reduce BRD incidence in feedlots and subsequently improve cattle performance and carcass characteristics has been relatively well documented [26, 27], metaphylaxis is facing more and more public scrutiny due to the increased antimicrobial resistance in BRD pathogens, as well as increased public and scientific concerns regarding the overuse of antimicro-

Bacterial vaccination is another common practice for the prevention of BRD in feedlot cattle in North America. There are a number of commercial vaccines available against *M. haemolytica*, *P. multocida*, *H. somni* and *M. bovis* [28]. These vaccines are made from bacterins or killed whole bacterium. Bacterial vaccines are less frequently used in feedlots compared to virus vaccines. This might be due to the controversial and limited efficacy of these vaccines against BRD bacterial pathogens [28].

**2.3 Current challenges associated with BRD prevention: antimicrobial resistance**

Despite advances in antimicrobials and vaccines, increased metaphylactic use and best management efforts to mitigate BRD, the prevalence of BRD in feedlot cattle continues to be increasing [9]. Although data are lacking, one contributor to increased BRD prevalence might be the development and spread of AMR in BRD pathogens. Recent studies have shown the emergence of BRD bacterial pathogens that are resistant to all classes of antibiotics used to treat BRD. For example, *P. multocida* strain isolated from a cow that died of BRD in Alberta has shown resistance up to five different antibiotics commonly used to control BRD (Alexander lab, unpublished data). *M. haemolytica* isolates isolated from Canadian and the US feedlots also exhibited resistance to more than three antibiotics [12, 13, 29]. Multidrug-

resistant *H. somni* isolates have also been detected in Albertan feedlots [13].

(n = 107) BRD [13]. Likewise, Anholt et al. [31] observed that 100% of the

*M. haemolytica* (n = 233), *P. multocida* (n = 117) and *M. bovis* (n = 226) and 67% of the *H. somni* (n = 75) isolates isolated from both living and dead BRD-affected cattle, originated from 60 different commercial feedlots in southern Alberta, exhibited resistance towards at least one antimicrobial class. Over 90% of all isolates (n = 745) displayed resistance to macrolide antimicrobials, which are the class of antibiotics

The prevalence of multidrug-resistant BRD bacterial pathogens is relatively high and increasing in both Canadian and the US feedlots over the years [30]. A recent study conducted in commercial feedlots in Alberta, Canada, revealed that there were significantly high levels of resistance (>70%) against tulathromycin and oxytetracycline in *M. haemolytica* and *P. multocida* isolates and high levels of resistance against oxytetracycline (67%) and penicillin (52%) in *H. somni* isolates isolated from the lower respiratory tract of feedlot cattle with (n = 210) and without

*DOI: http://dx.doi.org/10.5772/intechopen.81718*

bials in livestock production.

*Bovine Respiratory Disease in Feedlot Cattle: Antimicrobial Resistance in Bovine Respiratory… DOI: http://dx.doi.org/10.5772/intechopen.81718*

is defined as the mass treatment of an entire group or population of cattle with an antimicrobial to prevent and minimize an expected outbreak of disease [26]. Overall, 59.3% of feedlots in the USA with a capacity of >1000 head cattle use injective metaphylaxis, with approximately 21.3% of the cattle placed in the feedlot, receive metaphylactic antibiotics [6]. In Western Canada, more than 80% of the cattle in some feedlots receive injectable metaphylactic antibiotics on arrival to the feedlot (Personal communication with Dr. Steve Hendrick, Coaldale Vet Clinic, Alberta, Canada). The decision for metaphylactic intervention is primarily based on the nature of cattle population arriving at the feedlot. Cattle populations that are lighter body weight, multiple sources origin, and have poor health history and experienced long distance travel are often subjected to metaphylactic treatment at feedlot entry [26]. Metaphylactic treatment reduces BRD-associated morbidity and mortality by eradicating the already existing bacterial infections and preventing colonization and proliferation of pathogens in those immunosuppressed and vulnerable animals. Although efficacy of metaphylaxis to reduce BRD incidence in feedlots and subsequently improve cattle performance and carcass characteristics has been relatively well documented [26, 27], metaphylaxis is facing more and more public scrutiny due to the increased antimicrobial resistance in BRD pathogens, as well as increased public and scientific concerns regarding the overuse of antimicrobials in livestock production.

Bacterial vaccination is another common practice for the prevention of BRD in feedlot cattle in North America. There are a number of commercial vaccines available against *M. haemolytica*, *P. multocida*, *H. somni* and *M. bovis* [28]. These vaccines are made from bacterins or killed whole bacterium. Bacterial vaccines are less frequently used in feedlots compared to virus vaccines. This might be due to the controversial and limited efficacy of these vaccines against BRD bacterial pathogens [28].
