Farm Animal Medicine and Surgery. Graham R Duncanson
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to be infected under 2 years of age. The disease has an insidious onset with just a slight change of character. Full-blown signs of aggression and paraplegia are often brought on by parturition. Diagnosis other than that from clinical signs relies on histology of the CNS. The disease is similar to Creutzfeldt-Jakob disease (CJD) in man and is notifiable in the UK.
Listeria monocytogenes
L. monocytogenes causes a very serious zoonotic disease, with animals showing neurological signs, pyrexia and abortion. Animals can pick up the organism from other animals but the normal spread is from contaminated silage. The most prominent neurological sign is circling and a raised rectal temperature. Diagnosis can only be confirmed by culture from a cerebrospi-nal fluid (CSF) tap. Treatment should consist of high levels of oxytetracyclines and NSAIDs. See also ‘Bovine iritis (silage eye)’ under ‘Ocular conditions’ below, and ‘Abortion and its causes’ under ‘Diseases of the Reproductive System’.
Nervous acetonaemia
This is a metabolic disease of dairy cows (see below).
Obturator nerve damage
This occurs during parturition of a relatively fetal oversized calf and may be linked to sciatic nerve damage (see below). The obturator nerve controls the motor function of the muscles that adduct the hind legs, so that the animal does the splits and lies down in sternal recumbency like a frog. Immediate treatment is vital to prevent further nerve damage; it should consist of NSAIDs and securing the hind legs with ‘Somerset shackles’. These should be adjusted to prevent the legs from abduction by more than 40 cm for a large cow.
Rabies
This is caused by a rhabdovirus, and where the virus occurs is the most important cause of encephalitis in cattle, thanks to its zoonotic implications. Cattle are infected by a bite of an infected carnivore and invariably die. They exhibit both the dumb and the furious signs. Cattle are a particular danger to man as they excrete the virus in their saliva, which is produced excessively and gives the appearance of an oesophageal foreign body. There is no treatment but there is a vaccine available although it is not licensed in the UK. The disease is notifiable in the UK.
Sciatic nerve damage
Damage causing paralysis occurs in the pelvic canal during parturition. Both the sciatic and the obturator nerve may be damaged, causing ischiatic paralysis. The signs will include abduction of the hind legs together with the hock being overextended and the fetlock partially flexed. Treatment involving NSAIDs and a high level of nursing needs to be instituted immediately. The cow needs to be moved either outside if the weather is clement or on to a deep muck bed. The prognosis will be related to the severity of the clinical signs. A rising serum creatine kinase (CK) level indicates a very poor prognosis.
Ocular conditions
Besnoitosis
Apart from cysts in the sclera conjunctiva, this disease can be asymptomatic. Cattle can show an initial acute phase with generalized skin oedema, swollen lymph nodes and a reluctance to move. This may lead to a chronic phase of alopecia, skin thickening with wrinkles and cracks, and hyperpigmentation. Besnoitosis has been reported in Africa, Asia and South America, and very sporadically in south-west Europe. The cat is the normal intermediate host, and infects cattle by contaminating feed-stuffs. Biting insects may also spread the condition. Diagnosis is from the cysts in the sclera, which are pathognomic. Treatment is with oxytetracyclines and supportive nursing. See ‘Protozoal skin diseases’ under ‘Diseases of the Integument’ below, for further information.
Bovine iritis (silage eye)
This condition is seen in cattle fed silage contaminated with the bacterium L. monocy-togenes, particularly when the silage is fed in ‘ring feeders’. Normally both eyes are affected. Diagnosis can be confirmed by observing the iritis with an ophthalmoscope. Treatment is with a sub-conjunctival injection of atropine sulfate and dexamethasone.
Congenital cataracts
These occur as a result of an autosomal recessive gene seen in Friesians, Holsteins, Jerseys and Herefords.
Foreign bodies
These are normally oat flights (see Plate 1). Careful removal needs to be carried out under sedation and local anaesthesia.
Horner’s syndrome
This is a syndrome-associated interruption of ocular sympathetic nerve pathways. The signs are miosis, enophthalmos and loss of sweat on the ipsilateral side of the muzzle. The normal cause is trauma to the neck or abscesses in the chest or behind the eye. If the root cause is an abscess that should be drained and the animal given antibiotics. If the cause is trauma, NSAIDs would be appropriate treatment.
Infectious bovine keratoconjunctivitis (New Forest eye)
This is the most common ocular disease in cattle in the UK. There are several theories on the cause. One eye is normally affected, with approximately 10% of affected cattle having some signs in the other eye. Initially there is excess lacrymation followed by corneal damage. The condition is spread by flies. Many animals will self-cure. There are various accepted treatments:
• long-acting antibiotic eye ointments
• sub-conjunctival injections of antibiotics
• parenteral injections of long-acting antibiotics
Squamous cell carcinoma of the third eyelid
This is the most common tumour affecting the bovine eye worldwide. It occurs in non-pigmented third eyelids, e.g. in Herefords, and is more prevalent in the tropics. If the condition is noticed early enough the third eyelid can be cut off with sharp scissors under sedation and local anaesthetic blocks. Provided the tumour can be removed totally leaving a margin on the third eyelid the prognosis is good. Otherwise, enucleation is required.
Thelazia spp.
These nematodes live in the lacrimal ducts and are spread by flies. They have a worldwide distribution mainly in the tropics and subtropics, and cause conjunctivitis and keratitis. Treatment is with ivermectins parenterally.
Vitamin A deficiency
This is rare except in totally barley-fed bulls and bullocks. There is a retinal degeneration which is irreversible.
Metabolic Diseases
These can also be viewed as a category of neurological conditions.
The predominant signs
• Anorexia
• Lack of rumination
• Ataxia
• Recumbency
Acetonaemia
This is also called ketosis as by definition there are raised levels of ketones in the blood and milk, which can be demonstrated in the latter by Rothera’s powder turning purple. Acetonaemia is primarily a condition of dairy cows either too fat at calving and with an