BRD is defined as a “disease complex”. It is usually caused by a variety of pathogens including viruses, bacteria and lungworm.
- The viral agents commonly associated with BRD include Bovine Respiratory Syncitial Virus, Parainfluenza 3 & Bovine herpes virus 1 (BoHV-1 which causes infectious bovine rhinotracheitis). While Bovine Viral Diarrhoea virus isn’t a primary respiratory pathogen, acute BVDv infections cause immuno-suppression rendering the animal more vulnerable to other diseases including pneumonia.
- The bacteria associated with acute pneumonia outbreaks include Pasteurella multocida, Mannheimia haemolytica, Histophilus somnus, Mycoplasma bovis while Arcanobacterium pyogenes may be found in chronic cases.
- Parasitic lungworm caused by Dictyocaulus viviparous, is common particularly in the latter part of the grazing season in young stock and also in dairy cows whose immunity has waned. It is not uncommon in dairy cows for a partial loss of immunity to lungworm, combined with a significant challenge from larvae on the pasture to lead to a re-infection syndrome where animals show signs typical of lungworm but never have any lungworm larvae in the faeces. This is because the cow’s immune system is unable to mount a sufficient immune response to prevent larvae reaching the lungs but the immune response prevents the larvae maturing into egg laying adults.
While bacterial pathogens may be the primary agents in some cases of pneumonia, such as in transit/ shipping fever, in many outbreaks the viruses mentioned above act as primary agents with bacteria coming in on the back of compromised respiratory defences due to the viral damage.
Also in many outbreaks of BRD contributing factors such as the stress of weaning, change in diet and variation in ambient temperature and humidity play an important role plus in young calves inadequate colostrum intake is still a common problem on farms. While passive immunity may not be fully protective against viral pneumonia it will help reduce the threat of bacterial pneumonia in young calves.
BRD manifests in numerous ways in cattle, depending on the age of the animal, causative organism(s) and stage of the disease.
- Reduced appetite- Often the first sign- e.g calves slow to drink their milk, suckler cow not properly sucked or animals slow to come to the trough to feed
- The connection between BRD and fever is extremely strong. BRD is one of the most common causes of fever - and fever is often one of the earliest signs of the BRD particularly of viral origin. However animals affected with Mycoplasma bovis may only have a mildly elevated temperature (102.5°F). Animals with chronic pneumonia or end stage pasteurellosis may have normal or in some cases subnormal body temperature.
- Rapid, shallow breathing
- In the early stages of lungworm coughing is marked particularly after exercise.
- Animals with viral pneumonia with often have a prominent harsh cough, while those with bacterial pneumonia may initially have little coughing but when they start to recover they will start to cough up the mucus and pus which has built up in the lungs. In early BRD cases, the lungs and airways are generally painful, so the animal will try to clear the airway with mild, tentative coughing.
- Animals with chronic pneumonia often also have a chronic pronounced cough, at which point treatment is difficult.
- Nasal discharge - Serous initially with viral pneumonia progressing to purulent when secondary bacterial agents are involved. Discharge from the eyes is common with IBR.
- Salivation due to difficulty swallowing either because of pain in the throat or difficulty breathing - “air hunger”.
Diagnosis may be made on clinical signs and epidemiology, but additional tests are often needed (e.g., alveolar washings, nasopharyngeal swabs, blood samples, post-mortem examinations). The key is involving the vet early in the time course of the disease outbreak to take meaningful samples which will aid in making a diagnosis.
Treatment should always be carried out in consultation with your vet who may prescribe antibiotics plus non steroidal anti-inflammatory drugs for acutely sick animals. Anthelmintics may be needed if lungworm is suspected and in some cases lungworm can cause disease even in the absence of larvae in the faeces.
Along with this, symptomatic treatment such as ensuring sick animals are put on a straw bed in a well ventilated draught free shed with easy access to fresh water and feed will help aid recovery.
In some cases vets may recommend treatment of the whole batch with antibiotics depending on their clinical judgment, especially if a number of animals in the group are sick. When choosing an antibiotic in many cases a long acting perhaps more expensive initial treatment may pay back in the longer term with better long term cure rates and animal performance.
Traditionally cheaper antibiotics were used initially and if animals failed to respond, then more expensive antibiotics were used but there is an argument for using a more expensive product first when the chance of a cure is better rather than reserving premium products for end stage chronic cases, many of which will end up dying at some stage anyway. This practice of using more expensive products first line is common place in larger units in USA where they have also introduced the concept of “Post treatment Intervals”.
The principle of applying a post treatment interval is that there is a period of time after treating an animal when, (assuming a proper dose based on the weight of the animal has been given and the product is broad spectrum covering all the common pathogens associated with that condition), it has effective antimicrobial levels in the lungs. On units adhering to post treatment intervals unless the animal is obviously worse in the days following treatment it isn’t eligible for re-treatment until the antibiotic has reached the end of its duration of action, e.g. an antimicrobial lasting at least 9 days would have a 9 day post treatment interval. They have found that this has significantly reduced total drug bills in treating BRD outbreaks and also sick animals are left to recover in peace plus there is reduced labour and in the longer term there is no impact on animal performance
The key to minimising the impact of bovine respiratory disease is-
- Colostrum management in newborn calves
· Aim to give calves 1 litre per 10 kg body weight within 6 hours of birth- calves will weigh on average 40 kg depending on breed, etc.
- Reduce “stress”-
· Ensure animals are eating enough concentrate prior to weaning
· Avoid dehorning or castration in the 3 weeks before or after weaning
· Wean calves and leave them in the same environment if possible for at least a week.
- Vaccination- There are many different options for vaccination schedules but here are some guidelines to bear in mind when discussing a vaccination plan with your veterinary surgeon
· Cover the most likely pathogens (assess risk for the farm system or review previous lab results)
· Get immunity in place before the challenge
i. Young dairy bred calves need immunity in place before they are weaned at around 6 weeks of age.
ii. Spring born suckled calves should be vaccinated pre-weaning whether they are to be kept on the rearing farm or sold through a market.
iii. While pneumonia occurs all year round viral pneumonia outbreaks in calves often are worst in damp, still wintry weather.
· Vaccinate ALL animals in the same air space as vaccination reduces disease but just as importantly it reduces viral shedding from infected animals and therefore challenge.
· Over-whelming challenge will lead to disease even in vaccinated stock
· Age effect: passive immunity acquired from colostrum interferes with injectable vaccines hence the benefit of intranasal vaccines in young calves both for rapid early onset of immunity and to minimise the impact of maternal antibodies on the response to vaccination
· Impaired immune response- Purchased animals have often been mixed and stressed hence they are vulnerable to pneumonia and need rapid protection ideally by intranasal vaccination. However if purchased animals are stressed their ability to respond to vaccination may be impaired. These animals need adequate rest, feed and water (especially after transport/ markets)
- Proper housing- The key elements are
· Ensuring the air is as fresh and dry as possible (pathogens survive longer in damp stale air). Some points to bear in mind include
a. Wider span buildings are harder to ventilate; the stack effect starts to fail at >25m span
b. The steeper the pitch of the roof the better
c. Ensure outlet is at least 1.5 m above inlet and at highest point in shed
d. Inlets should be along the whole length of the shed
e. Remember stack effect won’t work as well if temperature difference is small between inside and outside of the building.
· Avoid draughts.
· Where possible house different age groups in separate air spaces and adopt an all in all out policy.
· Avoid over crowding and ensure calving pens, calf pens and creep areas for suckled calves are always well bedded.Anthelmintic therapy for animals vulnerable to lungworm particularly in the latter part of the grazing season, e.g. Moxidectin Pour On is licensed for use up to 5 weeks prehousing with no need to re-treat for worms at housing.
In the UK, BRD costs the cattle industry £80 million annually1. A survey published ten years ago estimated the cost at £82 per suckler calf affected and £43 per dairy bred calf 2.
Interestingly the single biggest component in each age group was loss in future performance. Ironically the figure quoted for dairy bred calves in this study may be an under-estimate when considering dairy heifer replacements.
Another Dutch scientific paper has estimated that BRD in the first 3 months of life causes on average a 2-week delay to 1st calving and a 2.2% reduction in milk yield in dairy heifers. Based on current economics for an average heifer which has the potential to give 6000 litres in her first lactation this would equate to a further loss of over £503.
Why is pneumonia a problem only on some farms in some years?
While the causal agents are ubiquitous, the disease in truly multi-factorial. Whether disease occurs depends on the level of challenge and the level of immunity. Naïve young stock which are stressed will be much more vulnerable and once one animal is sick it increases the challenge to other animals in the group.
Why is it worst at certain times of the year?
Pneumonia can occur all year round but disease incidence is higher in the winter because-
- Housed animals are in closer contact
- The air is often damper in winter and lower pressure plus less UV light favouring virus survival.
When should I start vaccinating?
Animals need to be healthy when vaccinated and vaccines work best if the immunity is in place before the disease challenge. Also vaccination for viral pneumonia reduces shedding of the virus should that animal be exposed to disease hence minimizing disease build up on a unit.
What if I only vaccinate the replacement heifers and leave the bull calves unvaccinated in the same shed?In many cases the unvaccinated animals may develop disease and the challenge to the vaccinated animals may be such that they also develop less severe disease
How do I know which vaccine is best for my farm situation?
Consult your vet who can advise you which pathogens are threats in your particular farm situation and also which types of disease you can vaccinate against.
What can I do to control Mycoplasma bovis?
Ideally avoid introducing it onto your farm but if it does then batch treatment with an antibiotic licensed to threat Mycoplasma bovis in consultation with your vet may be necessary early in the time course of the disease
1Barrett D.C (1997) RCVS DCHP Thesis 3.Zoetis market research 2005
2Andrews A.H. (2000) Cattle Practice Vol 8 Part 2: 109-114
3Van der Fels-Klerx et al Livestock Production Science 75 (2002) 157-166
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