Bovine Respiratory Disease

Published on Wed, 08/02/2017 - 11:17am

Bovine Respiratory Disease

Article provided by Dr. Murray Jelinski and Dr. Eugene Janzen

Bovine Respiratory Disease (BRD) is the most common and costly disease affecting the North American beef cattle industry. In the broadest sense, BRD refers to any disease of the upper or lower respiratory tracts. BRD is commonly associated with infections of the lungs causing pneumonia in recently weaned and feedlot cattle, nursing beef calves, housed dairy calves, and lactating dairy cows.

BRD is a complex multi-factorial disease that involves an interaction between several factors, including:
Host factors (characteristics of an animal that make it more prone to the disease): age, immune status, prior exposure to the pathogens, genetics, etc.
Environmental factors (transport, commingling, temperature fluctuations, crowding, ventilation, auction-sourced, etc.)
Infectious agents (disease causing organisms or pathogens) such as:
• Viruses, including: bovine herpesvirsus (IBR); bovine parainfluenza virus (PI-3); bovine respiratory syncytial virus (BRSV); bovine viral diarrhea virus (BVD), and bovine coronavirus (BCV).
• Bacteria, including Mannheimia haemolytica, Pasteurella multocida, Histophilus somni and Mycoplasma spp.
• Parasites, including lungworm

Clinical Signs
Historically, feedlot cattle exhibiting signs of depression separate themselves from the rest of the pen. Most of the time, this would occur within the first two weeks after arrival in the feedyard. Body temperature has been used to determine whether they should be treated. Body temperature is such an important diagnostic test that many feedlots will treat animals based upon an undifferentiated fever (UF).
Classical clinical signs of bacterial BRD include:
• Fever of over 40°C (>104°F)Subscribe to the Beef Research blog
• Difficulty breathing occurred to varying degrees
• Nasal discharge
• Varying degrees of depression
• Diminished or no appetite (‘off-feed’)

Currently, BRD may not always be “arrival associated” and frequently occurred after the stock attendants have diminished their surveillance of the newly arrived animals. In addition, early selection of sick cattle has become much more difficult because the current causative agents don’t produce the same degree of toxemia that creates the “tell-tale” depression, which is so useful to identify sick cattle. Hence, the early signs of depression and slight breathing difficulty are easier to overlook. Often times, when selected, cattle will display a profound exercise intolerance (hard to get out their “home” pen), obvious breathing difficulty, very little evidence of appetence and show a poor or prolonged response to treatment.

Risk Factors
Ultimately, a mixture of disease organisms is usually responsible for the respiratory infection and illness, but a number of other factors influence the animal’s ability to withstand the infection and illness. Any one risk factor alone may be insufficient to trigger cases of BRD, but together they form an additive effect that can predispose the animal to BRD.
Environmental factors, particularly transport, have been associated with BRD for decades. Therefore, BRD may also be referred to as ‘Shipping Fever’. A study involving calves arriving at 21 US commercial feedlots from 1997 to 2009 concluded that distance traveled was correlated to BRD, average daily gain (ADG) and hot carcass weight (HCW). This, however, has not been substantiated in western Canada.
Weather has always been implicated in the occurrence of BRD, presumably because the greatest incidence of BRD occurs during the fall. However, this finding is confounded by the fact that it is also when the greatest number of calves is being assembled, mixed (commingled), and transported. A study involving 288,388 head of cattle, arriving at 9 US commercial feedlots during September to November in 2005 to 2007, found that maximum wind speed, mean wind chill temperature, and temperature change were associated with an increased incidence of BRD.
A number of studies have found a higher incidence of BRD in auction market versus ranch-derived calves. Furthermore, the incidence of BRD increases with the level of commingling; calves assembled from multiple lots are more likely to get BRD than are pens of calves composed of larger groups of calves. In addition, there is considerable anecdotal evidence that the quality of the calves purchased is highly associated with the incidence of BRD; with poorer quality calves having more BRD.
A preponderance of studies found that lighter weight calves have a higher risk of developing BRD than do their heavier penmates.
A large-scale U.S. study involving 21 million animals found that from the years 1997-1999 females were at a greater risk of developing BRD than were males, but no difference in gender was found for the years 1994-1996.
Most studies looking into the effects of dehorning and castration only examined performance parameters (ADG, feed:gain); however, it is inferred that these stressful events, and others like calving or an overenthusiastic introduction to high grain rations, may precipitate cases of BRD.
The risk factors associated with an outbreak in a particular feedlot may or may not exist in outbreaks involving similar types of animals in similar settings.

Preconditioning appears to have some benefit in preventing BRD, with weaning prior to the sale being the most important component of a preconditioning program. The concept of preconditioning calves to decrease stress levels was first introduced in 1967. While there is considerable variation in what constitutes a preconditioning program, the central components entail:
• Vaccination for respiratory viruses and bacteria
• Weaning days to weeks in advance of sale
• Administration of clostridial vaccines
• Dehorn and castrate far enough in advance of sale for complete wound healing
• Training calves to bunk feeding
The concept of preconditioning has been largely accepted in Alberta; many feedlots prefer to “place” calves in winter (January, February) recognizing such groups of calves have very likely been weaned and “bunk broke” thus completing the most important management aspect.

After Calves Arrive at the Feedlot
Vaccines for respiratory diseases are routinely administered upon arrival at the feedlot, which may also be a difficult time for a stressed calf to mount an effective immune response. A recent review of the scientific literature found no clear benefit from vaccinating calves upon arrival at the feedlot. Another review relating to Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni vaccines concluded that there was a potential benefit for vaccinating feedlot cattle against M. haemolytica and P. multocida but not H. somni.
Nutrition may affect incidence of BRD. One review found that increased energy density (concentrates) will improve ADG without adversely affecting the incidence of BRD. Other studies found that the incidence of BRD tended to increase once concentrates exceeded 50% of the diet. Similarly, BRD morbidity increased once crude protein exceeded 14%.There is not enough evidence to conclude that injected doses of vitamins A, D, and E willreduce BRD. A wide range of studies have also examined supplementing with potassium, thiamine, B-vitamins, copper, zinc, vitamin E, selenium, and bypass protein, but none have significantly affected the incidence of BRD.
Metaphylactic treatment strategies can help control BRD in high risk calves, but feeding oral antimicrobials, either by water or feed, may not be effective. An analysis conducted in the early 1990s concluded that there was a lack of studies to justify the use of mass medicating with oral antimicrobials. Two subsequent studies found that inclusion of chlortetracycline and sulfamethazine in the ration reduced BRD treatments and morbidity. The cost and perceived over-use of antimicrobials in agriculture may limit the future use of oral antimicrobials.

The literature contains a large body of knowledge regarding the beneficial effects of antimicrobial therapy in the treatment of BRD. The question is not, whether to treat with an antimicrobial, but rather, “which antimicrobial works best?” There is no simple answer to this latter question.
Ancillary drugs, such as nonsteroidal anti-inflammatories (NSAIDS) and immunomodulators, have been used to treat BRD for decades. However, many of the studies have been used on experimental models and there is a lack of data from well-designed, large-scale, clinical trials. That said, a more recent study found that meloxicam (NSAID) administered prior to castration significantly reduced the number of animals to develop BRD.
Recommendations regarding the use of specific antimicrobials must come from a veterinarian. However, the veterinarian’s role is often altered to an examination of “Why treatments fail?” rather than, “How should animals be treated and with what?” Common causes of treatment failure include;
• Pathology of the lesion too far advanced
• Wrong diagnosis
• Simultaneous disease process (e.g.: Overt IBR, Post calving metritis)
• Inadequate dosage (e.g. MIC for the organism is higher than “label dose”)
• Overuse or inappropriate use of Ancillary Pharmaceutics