Yes, it’s a mouthful, but “neurological” just means “relating to the central nervous system”, and the central nervous system consists of the brain and spinal cord. So neurological signs in animals are the clues the animals give us that there is something wrong with their brain and/or spinal cord. And of course, because the central nervous system is such a complex structure, the signs of abnormality in it are many and various. Adding to the complexity is the fact that there are many possible causes of brain and cord damage, including traumatic injury, poisons, infections and abnormal metabolism. You can see that it is difficult to summarise what causes neurological signs what to do about them.
Possibly the most helpful thing I can do in a short article like this is to list the most common causes of neurological signs in livestock and indicate the probable cause and the type of treatment required. This may give you an idea what to expect when you consult a veterinarian.
Regardless of the cause, an animal with brain damage will usually show abnormal behaviour and/or abnormal movements. (For this reason, I prefer the term “neurological signs” to “nervous signs”. “Nervous signs” somehow implies nervousness or anxiety, when anxiety is only one of the many different signs that brain damage can cause.)
An animal showing neurological signs may seem confused, it may be unusually dull or unusually agitated. It may have a fine tremor of the head and maybe neck, it may be staggery or it may appear drunk. It may be partially or completely paralysed. It may be partially or completely blind.
Spinal injuries usually cause partial or complete paralysis and/or sensation of the part of the body below the injury. Changes low in the cord usually cause hind limb problems, and the higher the injury is the more of the body is affected.
Some of the more common causes of neurological signs in cattle
- Polioencephalomalacia (PE) is a disease caused by vitamin B1 deficiency in ruminants like cattle, sheep and goats, often triggered by a change in feed that leads to a reduction in the amount of thiamine or vitamin B1 in the rumen. The signs include blindness, dullness, aimless wandering. It’s important to get the animal treated as soon as the signs appear, and this means thiamine injections by your vet.
- Ryegrass staggers is caused by toxins (poisons) produced by an endophyte (a type of fungus) in some types of ryegrass. The disease occurs in late summer/autumn (January to March) in all but the south half of the South Island. The signs are tremors and staggering in cattle, sheep and deer, and alpacas and horses are particularly susceptible. Affected animals are susceptible to paddock accidents like getting caught in electric fences or falling into streams. Treatment involves getting affected stock off the ryegrass pasture they are on and onto some other type of feed or endophyte-safe ryegrass.
- Metabolic diseases such as acetonaemia (sleepy sickness), milk fever (hypocalcaemia) and grass staggers (hypomagnesaemia) generally occur most often in cows and ewes around the time of birth They cause sudden death or neurological signs (ranging from extreme dullness in acetonaemia to unusual agitation and convulsions in hypomagnesaemia) and the animal eventually goes down, unable to rise. Urgent treatment by appropriate injections is needed.
- Bacterial meningitis in young calves can be caused by infection from a wound such as a castration wound. Antibiotic treatment may be successful in cases treated early.
- Lead poisoning can be caused by licking old lead paint (most common in calves kept indoors) or licking old vehicle batteries. Treatment is prolonged and difficult but your vet can inject substances to help remove the lead from poisoned animals.
- Hepatic encephalopathy is a mouthful for a disease in which neurological signs develop as a result of severe liver damage (e.g. ragwort damage). The liver damage leads to toxins circulating in the blood and these cause abnormal behaviour. No treatment is possible apart from TLC (tender loving care).
- Traumatic injury to the head or back is fairly common and the signs that result reflect the site and degree of damage done to the brain or cord. In mild cases there may be some improvement with time and good care.
Some of the more common causes of neurological signs in sheep
- Listeriosis (a bacterial infection of the brain causing staggeriness and dullness and possibly aimless circling, often associated with eating poor quality silage). Antibiotic treatment from your vet may help in early cases.
- Bacterial meningitis and brain abscesses can occur in sheep of any age. The infection may have spread from a wound or from a disease somewhere else in the body. Very early cases may respond to antibiotic treatment by your vet.
- Spinal abscesses in lambs can result from spread of infection from a tailing or castration wound. The affected lamb becomes completely or partially paralysed usually in the hind end.
- FSE (focal symmetrical encephalomalacia) - a form of delayed pulpy kidney disease that cause neurological signs. There is no cure but it can be prevented by clostridial vaccination.
- Tetanus is caused by clostridial bacteria in deep wounds, and it’s commonly associated with docking or castration wounds. The signs are gradual onset of stiffness leading to a rigid rocking horse position then death. The disease can be prevented by clostridial vaccination.
- PE, ryegrass staggers, metabolic disease, meningitis – as for cattle.
- Trauma as for cattle; see above. Occasionally rams can break their neck when fighting
Some of the more common causes of neurological signs in deer
- Malignant catarrhal fever is caused by a type of virus carried by sheep. It results in a wide range of signs from sudden death to dullness and dysentery. There is no cure and it is nearly always fatal.
- PE and ryegrass staggers can occur in deer as in cattle (see above).
- Trauma is a relatively common cause of neurological signs in deer. See above. Because of their flighty nature there is an in creased chance of deer being injured especially when being mustered and yarded. The aggressive behaviour of stags during the rut can also predispose to injury.
Some of the more common causes of neurological signs in horses
- Ryegrass staggers and trauma are probably the most common causes of neurological signs in horses. See above.
- Because horses are sometimes kept to a ripe old age, brain tumours are probably more common in this species than in other types of livestock. The signs are many and varied, depending on their size and rate of growth and site in the brain.
Important: New Zealand is free of the transmissible spongiform encephalopathies (TSEs) such as ‘mad cow disease’ in cattle, scrapie in sheep and chronic wasting disease in deer, and that’s the way it should stay.
In order to provide evidence of New Zealand’s disease status regarding the TSEs, MAF is required to test a certain number of brains from livestock that have shown any of the signs consistent with these diseases. Consequently they offer financial incentives to farmers for the brains from cattle, sheep or deer that are over 2 years old and that showed neurological signs before death or euthanasia. So it is important that you report any adult cattle, sheep or deer with neurological signs to your veterinarian and he or she will take it from there. You may lose the animal, but you will get some financial compensation for it.