Farm Animal Medicine and Surgery. Graham R Duncanson
with antibiotics and NSAIDs should always be secondary to changes in animal husbandry, particularly modifications to ventilation, prevention of draughts and lower stocking rates. Causative agents include the viruses and bacteria in the following list:
• Bovine herpesvirus 1 (BHV 1) will cause respiratory disease, particularly in older growing cattle, which is called infectious bovine rhinotracheitis (IBR). It will also cause the reproductive disease infectious pustular vulvovaginitis (IPV). The respiratory form of the disease manifests as serious pyrexia with an ocular and nasal discharge. Remarkably, the clinical course of the disease is much improved by injections of a combination of penicillin and streptomycin. The disease is readily detected by serology, which can be used in herd eradication schemes. There are good vaccines which are available either as live vaccination for intra-nasal or im use or as attenuated dead vaccination for sub cut injection. Care should be taken to use a marker vaccine if later eradication schemes are envisaged. See also ‘Bovine herpesvirus 1 (BHV 1)’ as a cause of abortion under ‘Diseases of the Reproductive System’ below.
• Bovine respiratory coronavirus (BRCV) has only recently been recognized as a serious potential respiratory pathogen. It now needs to be considered when investigating a BRD outbreak.
• Bovine respiratory syncytial virus (BRSV -or just plain RSV) is a very serious pathogen, particularly for young growing cattle – either suckler calves or concentrate-fed animals. It causes serious pyrexia, coughing, and nasal and lacrimal discharge. Dyspnoea and mouth breathing is a feature of advanced cases. Passive immunity helps but does not prevent the disease. There are good vaccines available.
• Bovine parainfluenza virus 3 (PI3) is a paramyxovirus which causes relatively mild disease signs but is a prime initiator for secondary bacterial infections. There are good vaccines available.
• Infectious bovine rhinotracheitis (IBR) is caused by BHV 1 (see above).
• Mannheimia haemolytica (formerly Pasteurella haemolytica) is probably the most important bacterial pathogen in the BRD complex. It can cause disease in its own right without a viral initiator. It is the main pathogen causing ‘shipping fever’. It is actually sensitive to penicillin in high doses even through it is a Gram-negative rod. However, there are a large number of other suitable antibiotics which are perhaps more effective and have a considerably longer action. NSAIDs are very useful. There are vaccines available.
• Pasteurella multocida is a bacterium that is also often found in the ‘shipping fever’ complex. It is also seen as a secondary to BRSV and PI3 infections in younger calves. It can cause pneumonia in its own right. Like M. haemolytica it is sensitive to high levels of penicillin, but more modern antibiotics and NSAIDs would be more appropriate for treatment.
• Arcanobacterium pyogenes is found at the end stage of a BRD case, i.e. it is a tertiary pathogen. Although it is sensitive to antibiotics in vitro the bacteria are infective in pus-filled abscesses. Euthanasia is the only option.
• Histophilus somni is a serious bacterial pathogen in its own right but is often linked with M. haemolytica. The bacteria can cause BRD on their own or be secondary to a virus. H. somni often occurs later on in the disease process and is difficult to treat with antibiotics. Changing the type of antibiotic used and NSAIDs are helpful treatments.
• Mycoplasma spp. include M. disbar and M. bovis. These are emerging pathogens in BRD. They synergize with other pathogens and cause fatal disease. Oxytetracycline is the antibiotic of choice. They will also infect the joints, causing acute lameness in young cattle which are already systemically ill. NSAIDs are very worthwhile treatment. The species are not included in any vaccines.
• Ureaplasma spp. may have a secondary role in BRD but it is not clear how important they are in respiratory disease. They are more important in reproductive disorders.
Bovine tuberculosis
This very important zoonotic disease is found throughout the world and is notifiable in the European Union (EU), USA and elsewhere. It primarily affects the respiratory tract and associated lymph nodes. Historically, it was very important when it affected the udder and caused contamination of the milk. The main causative organism is Mycobacterium bovis, but other Mycobacterium spp. are also found. The disease can be spread by other wild mammals, e.g. badgers in the UK and opossums in New Zealand. It is a chronic wasting disease, only causing a cough and respiratory signs in the later stages. Peripheral lymph nodes may be enlarged. The disease is transmitted by the respiratory and ingestion routes. Herd screening is not easy as the standard comparative avian and bovine tuberculin intradermal test, as used in the UK, reveals false positives. The gamma inter-feron blood test is used as a follow-up. There is no treatment and affected animals should be slaughtered as soon as possible.
Contagious bovine pleuropneumonia (CBPP)
This very serious cattle disease is caused by Mycoplasma mycoides mycoides and is notifiable in the EU and the USA. It is found in Africa, India and China. It causes severe respiratory signs of coughing and an elbow abducted stance. There is a carrier state which can be confirmed by routine serology testing. On the whole, treatment with oxytetracyclines should be carried out after careful evaluation as this may increase the number of carrier animals.
The shipping fever complex
This is a specific serious respiratory condition that is separate from BRD. It is caused by M. haemolytica and Pasteurella multocida as noted above, and follows a stress, usually transport. Treatment is with oxytetracyclines and NSAIDs, and this is normally successful so more modern and expensive antibiotics are not required. There is a vaccine available.
Respiratory diseases caused by fungi and their treatment
Aspergillosis
This is extremely rare but will occur in very badly ventilated cattle sheds when mouldy straw is used. Actual hyphae will be seen in the lungs of this invariably fatal condition. A more common condition is a hypersensitivity reaction to the fungal spores which will give signs of acute respiratory distress similar to ‘fog fever’ in adult cattle. Fresh air and dexamethazone are the required treatment.
Respiratory diseases caused by parasites and their treatment
Lungworm (parasitic bronchitis)
This occurs 3 weeks after ingesting Dictyocaulus viviparus larvae. The excellent oral vaccination against this condition, which uses irradiated larvae, is sadly being neglected with the use of pour-on ivermectin-type anthelmintics. The animals at risk are 2 year old breeding heifers and, of course, adult cows. Lungworm causes devastating effects in naive adults, with very marked violent coughing. (Plate 2). Mortality may be as high as 10%. Treatment with anthelmintics, antibiotics and NSAIDs is often not very effective, with many survivors being left with irreversible lung damage.
Miscellaneous respiratory diseases, their causes and treatment
Anaphylaxis
This has a sudden onset of severe dyspnoea and muscle tremors. The rectal temperature will be raised to 42°C. The occurrence is normally linked either to a recent injection or is found in a dairy cow heavy in milk with a massively stocked udder. If the latter is the cause milking out will prompt a swift recovery. In other cases, animals should be injected with dexamethazone iv, or if pregnant with NSAIDs iv.
Fog fever
There are many theories on the aetiology of this condition of interstitial pneumonia. The theory with the most credence is that of a toxicosis resulting