Farm Animal Medicine and Surgery. Graham R Duncanson
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ingestion of large quantities of L-tryptophan in lush autumn grass. The disease occurs only in adults and the main sign is respiratory distress, with the rectal temperature remaining normal. It is a disease of beef suckler cows, and the affected animals tend to be separate from the rest, and are quieter than normal. Animals may be found dead or die following exercise. Care should be used in rounding up animals for treatment, which is far from evidenced based. Apart from more normal therapies, e.g. antibiotics, NSAIDs, steroids, etc., atropine and methylene blue have been advocated. In reality, the advice must be to stick to antibiotics and NSAIDs. The prognosis is guarded.
Inhalation pneumonia
This can occur when a cow is drenched carelessly with a liquid medicine, e.g. liquid paraffin or vegetable oil. It can also occur with a misplaced Agger’s pump. General anaesthetics (GAs) in adult animals are particularly hazardous. Inhalation pneumonia can occur in untreated ‘milk fever’ cases which have become bloated in lateral recumbency. The signs will vary from violent coughing to death depending on the volume of liquid inhaled. Treatment would consist of antibiotics and NSAIDs.
Diseases of the Circulatory System
Circulatory diseases with various causes and their treatment
Anthrax
This serious zoonotic disease is caused by a Gram-positive spore-forming bacterial rod called Bacillus anthracis and is notifiable in most parts of the world, including the UK. Ingestion is the most common method of infection, and there is very rapid extracellular multiplication of the bacteria, with toxin production and sudden death (although the author has seen a case that recovered which had been promptly treated after diagnosis by a colleague). Diagnosis is confirmed on staining a blood smear with McFadyen’s stain and seeing the rectangular rod-shaped bacteria with the blue-staining capsules.
Bleeding disorders
These are relatively rare and therefore represent a considerable diagnostic challenge for the clinician (Bell, 2011). In disorders of primary haemostasis, only a small amount of blood loss occurs from an injury site before a fibrin clot is formed by secondary haemostasis. Petechiae will be seen in the mucosa. In disorders of secondary haemostasis, large-volume bleeds will be seen in the body cavities. Primary disorders will cause thrombocytopenia, which is seen in acute bracken fern toxicity, acute infection with BVD virus, trichothecene mycocytosis, bovine neonatal pancytopenia (typically in calves under 1 month of age showing pyrexia and unexplained haemorrhage from the nose), ingestion of bone-marrow suppressive substances, e.g. furazolidone (now prohibited in the EU), and inherited bovine thrombopathia in Simmental cattle. Secondary disorders are seen in inherited deficiency of coagulation factor XI, Warfarin poisoning and mouldy sweet clover poisoning. Treatment is with blood transfusions (see Chapter 4).
Bovine leucosis
This is sometimes called bovine lymphosarcoma. There are two separate diseases recognized: bovine enzootic leucosis and bovine sporadic leucosis. Bovine enzootic leucosis is linked with a retrovirus and is spread by direct contact and dirty needles. It is a notifiable disease in the UK and is confirmed by agar gel immunodiffusion (AGID). The disease has been eradicated in most EU countries but is found in North America. Bovine enzootic leucosis is normally seen in older cattle, where it causes widespread tumours. There is no treatment. Bovine sporadic leucosis is seen in young growing calves, which exhibit swollen lymph nodes, salivary glands and thymuses. The disease causes rapid emaciation and death, and is confirmed at post-mortem.
Bovine petechial fever
This disease in endemic in Kenya and is caused by the blood parasite Ehrlichia ondiri. It is transmitted by an unknown arthropod vector from the bushbuck, Tragelaphus scriptus. The signs are petechial and ecchymotic haemorrhages on all the mucus membranes. There is some immunity as the disease only seems to infect animals brought into endemic areas. The treatment is with oxytetracyclines.
Cor pulmonale
This sporadic condition is right-side heart failure, normally following chronic pneumonia. The treatment is centred on the original cause of the condition together with frusemide as a diuretic.
Dilated cardiomyopathy
This is an inherited condition found in Holstein cattle. The signs are slow-developing peripheral oedema and pleural effusion, typically in 2-3 year old cattle. Diagnosis can be confirmed on ultrasonography. There is no realistic treatment and animals should be slaughtered.
Endocarditis
This is normally vegetative and caused by Arcanobacterium pyogenes. Diagnosis will be confirmed by auscultation and observing the peripheral signs which will vary according to which valve or valves are affected. The most common sign is engorged jugular veins. Treatment is a very prolonged course of antibiotics which seldom cure the disease. If the cow improves it is important that she receives full antibiotic cover at her next calving.
Heartwater
This is caused by a rickettsia, Ehrlichia ruminantium, which is spread by Amblyomma spp. ticks. It occurs in tropical Africa, the Caribbean, South and Central America and tropical parts of the USA. The disease is normally acute with a high fever and an increased vascular permeability, which causes hydropericardium and hydrothorax. These signs lead on to fatal neurological signs. Diagnosis is confirmed by the presence of the organism in Diff-Quik stained brain smears. Treatment is with high doses of oxytetracycline. Control is through effective tick control and vaccination.
Lightning strike
This assumes an over-importance in farmers’ minds in the UK as it normally is the only condition which their cattle are insured against. Sudden death in groups of cattle without signs of a struggle after a storm is reasonable evidence of lightning strike, particularly if they are all in contact with a wire fence. Burn marks may be seen on the medial aspects of the legs and haemorrhagic streaks will be seen on careful skinning.
Lyme disease
This condition is caused by the spirochaete Borrelia burgdorferi and is a worldwide zoo-nosis. It is not primarily a disease of cattle but will cause joint infection, which may be an immune-mediated response. Cattle will have swollen joints on their lower limbs and will be stiff on movement. Diagnosis is by PCR. Treatment with oxytetracycline for 3 weeks together with NSAIDs has been suggested.
Mycoplasma wenyonii
This condition is not fully understood and it is thought to be spread by arthropods or needles from mass vaccination procedures (Strugnell and McAuliffe, 2012). The main clinical signs in the UK are hind limb oedema, pyrexia and painful, swollen udders in dairy cows, with reduced fertility in stock bulls. Clinical signs gradually resolve and a full recovery may take 10 days or longer. Diagnosis is from fresh blood smears taken in a clean environment and stained with Giemsa. Treatment with 3 days of tylosin at 5 mg/kg im is said to be more effective than oxytetracycline at 10 mg/kg im.
Circulatory diseases caused by protozoa and their treatment
Anaplasmosis
The main organism causing this disease is Anaplasma marginale. It is tick borne and occurs in the tropics and subtropics. The main signs are pyrexia and anaemia. Diagnosis can be confirmed by thin blood smears stained with Giemsa. Treatment