DISEASES OF THE BRAIN OF CALVES D. C. Bloodt

(Continued from September)

DISEASES OF THE BRAIN wm SIGNS DEVELOPING IN CALVES ONE TO SIX MoNTHS OF AGE Calves of one to six months of age are the group in which most diseases of the central nervous system occur and it is these diseases which present the greatest difficulty in differentiation. Diseases in Which Generalised Cerebral Signs Predominate The syndrome presented is usually one of exaggeration of cerebral function and includes nystagmus, head-pressing or opisthotonus, , and clonic or tonic convulsions. The convulsions are marked by recumbency, paddling, champ- ing of the jaws and salivation. In rare instances there is mania with charging and bellowing. Signs suggestive of loss or depression of nervous function, par- ticularly blindness and , may also be apparent. Polioencephalomalacia is the most typical example of this group. It is charac- terized by swelling of the brain and necrosis of the deeper laminae of the cerebral cortex. The onset is quite sudden and is manifested by the appearance of blind- ness and periodic attacks of muscular tremor, opisthotonus and head-pushing. The temperature is normal and the heart rate characteristically slow. Within about 24 hours the animal goes down and has clonic convulsions with salivation, champing of the jaws and paddling with the limbs, either continuously or inter- mittently. These signs are accompanied by nystagmus and opisthotonus. The calf is blind but the pupillary light reflex is unaffected, suggesting a lesion of the optic cortex. Papilloedema may be evident on ophthalmoscopic examination but is-never marked. The calf is unable togtand, the limbs-are flaccid and, although sensation is normal there is no response to other external stimuli. This is the common syndrome in young calves, which usually die in two to seven days. Less severely affected and older animals usually remain standing and show blindness and head-pressing, and in the early stages some mania and occasionally localising signs. They often recover but are usually blind and imbecile. The disease is not restricted in its occurrence to calves. It can occur in cattle up to two years of age (13), in lambs (14) and in pigs (8), but the incidence is greatest in calves about six months of age, reared indoors. A high incidence has also been recorded in feedlot animals. The disease can occur at pasture but here, with the possible exception of its occurrence on rape in the late fall, it is less common and less severe. On rape grazing the syndrome is much the same but usually older cattle are pastured on this type of feed. Pulmonary emphysema and acute haemolytic anaemia occur more commonly on rape than does polioen- cephalomalacia (6). fOntario Veterinary College, Guelph, Ontario. 476 CAN. VET. JOUm., vol. I, no. 11, November, 1960 DISEASES OF THE BRAIN OF CALVES 477 The post-mortem appearance is that of acute cerebral oedema. The brain is swollen and enlarged, hanging over the sides of the cranium when the vault is removed, and the cerebellum is pushed back into the foramen magnum. The surface of the gyri are abnormally yellow-orange in colour in those parts of the cortex Nvhich have undergone pressure necrosis. These areas are often quite patchy but are usually symmetrical and most commonly involve the occipital cortex and the cortical motor area. The grey matter is whiter than normal and may be separated from the white matter. Although a normal or high intake of salt during a period of water deprivation is the probable cause of the cerebral oedema in some outbreaks, this is not so in at least 50 per cent of cases. On the basis that the cerebral oedema is meta- bolic in origin and dependent upon changes in tissue and intravascular elec- trolyte concentrations, due in some way to errors in diet, the standard procedure is to recommend a complete change of diet, the provision of ample drinking water and free access to salt or mineral mixtures. Polioencephalomalacia does not usually occur if these recommendations are followed. Decompression of the brain by administering acetazoleamide may be attempted and a cure may be effected if treatment is commenced early. Lead Poisoning. Poisoning with lead is by far the commonest cause of acute encephalopathy in calves and, provided access to a source of the poison can be demonstrated, there is usually no difficulty in arriving at a tentative diagnosis. Determining the source of the poison may present a very real problem and it may be virtually impossible to differentiate the condition from any of the others in this group, particularly polioencephalomalacia. The onset is usually more sudden, with tonic-clonic convulsions occurring in the very early stages and the course of the disease is short, 12 to 24 hours, so that many are found dead without signs having been observed. Blindness, opisthotonus, hyperaesthesia, muscle tremor and nystagmus are common to lead poisoning and polioencephalomalacia, but the emphasis in lead poisoning is on the severity and rapid progression of these signs, most calves being much more violent than-those affected .with polioencephalomalacia,-but. this is probably, not a completely dependable criterion. The severity of the signs in lead poisoning may depend upon the amount of lead ingested and some cases of polioencephalo- malacia can be quite violent in the middle stages and in older animals. At necropsy, levels of 40 p.p.m. of lead in the renal cortex are critical and indicate that fatal amounts of lead have been ingested. There is a complete absence of characteristic lesions in most cases. If there is any doubt clinically as to the cause of the disease and lead poisoning is a possibility there is no reason why treatment with calcium versenate should not be carried out. Poisoning with Organic Mercurials. This is a relatively common condition in pigs but the feeding of grain treated with organic mercurial seed dressings to cattle does not seem to be a common practice. Accidental ingestion of such grain on one occasion has no harmful effect but the disease can be produced experi- mentally by feeding over a long period. The clinical syndrome is indistinguish- able from that of lead poisoning but on necropsy there are characteristic degen- erative changes in the brain, kidneys and myocardium. 478 BLOOD Intoxication caused by Clostridium perfringens Type D. Enterotoxaemia caused by Cl. perfringens is rarely encountered clinically. However it may persist on a farm and sporadic deaths occur if vaccination is not carried out. As in lambs, the calves affected are fast-growing, in prime condition and being fed a highly nutritious ration. The onset is sudden with marked nervous signs in evi- dence. These range from a dummy syndrome with blindness and head-pressing to prostration, loud bellowing as though severe abdominal pain were present, severe clonic convulsions and sudden death (4). Again, the clinical picture is very similar to that of lead poisoning or poioencephalomalacia. The comparative rarity of the disease and the particular conditions of management under which it occurs may suggest it as a tentative diagnosis but laboratory confirmation, based on determination of the toxicity of filtrates of intestinal contents, is essential. Vitamin A deficiency as a cause of congenital disease of calves has already been described but the disease is probably more common in calves in this older age group. The characteristic nervous signs are tonic-clonic convulsions and hyperaesthesia, paralysis and blindness with papilloedema. Other signs includ- ing night blindness, xerophthalmia, dryness and scaliness of the skin, sometimes anasarca, weak or stillborn calves, placental retention and congenital defects should be apparent in the affected herd. . Tetanus is common enough in calves of this age group, often in asso- ciation with surgical wounds including castration, dehorning, and even ear- tagging. It is not a disease of the brain but is included here for purposes of com- parison. The clinical signs are characteristic and include of the limbs, opisthotonus, hypersensitivity to touch, bloat, prolapse of the third eyelid and the typical fluffing and holding out of the tail. Some cases of polioencephalomalacia resemble tetanus superficially but in the latter there is an absence of the blind- ness, profound depression and nystagmus which characterize the former. Sporadic Bovine Encephalomyelitis. There is probably as little justification for including this disease in a discussion of the diseases of the brain of calves as there is for excluding rabies and listeriosis. Although the disease is more common in other age groups, young calves are quite susceptible (10). The important lesions are pericarditis, pleurisy, peritonitis and meningo-encephalitis; these are manifested by high fever, pericardial and pleuritic friction rubs, pain over the abdomen, frequent urination and defaecation, scouring, and weakness with knuckling at the fetlocks, especially in the hind limbs. In young calves there may be visible enlargement of the peripheral lymph nodes and severe terminal de- pression and coma. There is a profound leucopenia in the early stages, with a marked depression of the neutrophil count. Treatment with oxytetracycline has appeared to cause rapid improvement, especially when two doses, each of two to five mgm. per pound body weight, are given 24 hours apart. Miscellaneous Poisonings. A number of poisons cause signs suggestive of in- volvement of the brain and are discussed briefly here as an aid to differential diagnosis. poisoning in calves is extremely rare due largely to absence of exposure to the poison, except where rabbits are a pest and the laying of baits composed of bran and strychnine is a common practice. DISEASES OF THE BRAIN OF CALVES 479 Tetrachlorethylene, hexachloroethane and carbon tetrachloride are used in the treatment of calves for internal parasites and occasional animals or groups of highly susceptible animals show signs of dullness, stupor, weakness, collapse, dyspnoea and rapid death. All of these poisonings are easily diagnosed because of the close relation of signs to dosing. Chlorinated hydrocarbons are quite safe to use but occasional cases of poison- ing in calves occur by misadventure, especially when the preparations are mis- takenly applied undiluted or are eaten when grasshopper baits are scattered about indiscriminately. The young of any species are more susceptible than adults. The clinical signs include muscle tremor and tetan'y, excitement, often to the point of frenzy, grinding of the teeth, dyspnoea, and frequent micturition. Terminally the animal becomes comatose. Repeated doses of pentobarbital sodium are recommended as treatment. Poisoning with organic phosphorus insecticides has assumed some importance because of the use of these substances in the control of warble ffies. Muscle tremor and tetany, salivation, sweating, severe dyspnoea, bloat, scouring, pupillary constriction and bradycardia are the typical signs in severe poisoning. The anti- dote is atropine in large doses repeated as required, but many mild cases recover quickly without treatment. Arsenic poisoning causes a severe gastro-enteritis and scouring but nervous signs often occur in the later stages. This may cause confusion with lead poison- ing but the emphasis clinically is on scouring, with tremor, inco-ordination and clonic convulsions occurring secondarily. Inherited Ideopathic Epilepsy. This disease has been observed in Brown Swiss calves which appear clinically normal until they are several months old but which subsequently develop typical epileptiform convulsions, especially when they are exercised or excited (1). These convulsive attacks disappear between the ages of one and two years. A typical epileptiform convulsion is comprised of three phases. In the premonitory phase there is apprehension and immobility. The con- vulsive episode follows, with tetany of the limbs and opisthotonus in the early stages immediately succeeded by clonic, paddling movements, champing of the jaws and salivation. The final phase is one of complete relaxation after which the animal appears dull but otherwise normal. Epilepsy usually results in little else than inconvenience although some deaths may be caused by misadventures. The characteristic pattern of epileptiform , and the normal appearance of the animals for long periods between seizures effectively sets this disease aside from most others. Inherited ideopathic epilepsy is conditioned by the inheritance of a dominant character. Diseases Characterized by the Presence of Localising Signs In the group of diseases just described the cardinal signs are those which suggest involvement of the brain, although there are no signs indicative of damage to a particular local area of the brain. Such signs include unilateral paralysis especially of the ears and face, deviation of the head, and convulsions which commence in, or muscle tremor localised in, particular parts of the body such as one limb. This is not a complete basis for differentiation. For example the blind- ness of polioencephalomalacia suggests involvement of the optic cortex and the 480 BIAOOD head-pressing of listeriosis suggests general involvement of the brain in spite of the circling and facial paralysis which are indicative of local micro-abcesses. One of the advantages of' separating, by clinical means, the signs of diffuse lesions from those of localised ones is that it does give some indication of the possible cause. Diffuse lesions are usually caused by acute cerebral oedemti (as in polioencephalomalacia), intoxication (as in lead poisoning) or encephalitis caused by a virus (sporadic bovine encephalomyelitis). Local lesions are usually caused by a bacterial encephalitis or abscess, often originating from a . Trauma and migrating parasite larvae are in an intermediate position and the signs which result depend on the severity of the damage. There may or may not be localizing signs. Abscess of the Brain. Sporadic cases of brain abscess occur and are usually due to infection with Sphaerophorus necrophorus which is either introduced by wounds such as those incurred during dehorning, or by haematogenous spread from lesions elsewhere in the body. Because the primary lesion is usually in the meninges with later spread to nervous tissue most cases show a combination of signs of irritation including head-pressing, blindness, mania and convulsions, and signs of loss of function including circling and facial paralysis. The latter usually predominate although this depends largely on the extent and severity of the tissue damage. The classical example of brain abscess is listeriosis which, how- ever, occurs rarely in calves. Because abscesses of the brain are usually bacterial, a moderate fever and toxaemia occur and there may be a leucocytosis. Examina- tion of a sample of cerebro-spinal fluid is valuable in making a diagnosis. The main difficulty is to differentiate a brain abscess from other lesions which cause localising signs. Otitis media is a typical example. The absence of signs of cerebral involvement helps to differentiate lesions of the peripheral nerves. Traumatic lesions of the brain are not usually accompanied by fever and toxaemia; the nervous signs are at their maximum early and then tend to subside. Otitis Media. Inflammation of the middle ear may develop by extension from the external ear or by localisation from the blood stream, and occurs in calves as young as one week of age. The classical signs are rotation of the head with the affected ear down, circling and falling to the affected side, and facial paralysis. A similar syndrome may occur when there is inflammation of the vestibular nerve nucleus in the medulla but there are two additional signs, nystagmus and forced circling. The medullary lesions usually develop because of spread from the middle ear and in either case treatment with a broad-spectrum antibiotic is usually sufficient to arrest further progress of the disease although recovery is not complete.

SUMMARY The more common diseases of calves in which the brain is affected are de- scribed, together with diseases of other systems which may be confused with them. Emphasis is placed on differentiation by clinical means and relevant information on history and necropsy examination is provided. DISEASES OF THE BRAIN OF CALVES 481 RÆSUME On donne la description des maladies les plus communes qui affectent le cerveau des veaux, de meme que celle des autres maladies des autres systemes avec lesquelles on peut les confondre. On insiste surtout sur les m6thodes cliniques pour etablir la diff6renciation, et on fournit tous les renseignements au sujet de l'histoire et de l'examen necropsique.

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COMING EVENTS January Meeting of the Ontario Veterinary Association to be held at the Royal York Hotel in Toronto on January 26, 27 and 28, 1961. September The 13th Annual Meeting of the Canadian Veterinary Medical Association will be held in Banff, Alberta, on September 9, 10, 11 and 12, 1961. 1962 The 14th Annual Meeting of the Canadian Veterinary Medical Association will he held in Guelph, Ontario, in conjunction with the centennial of the Ontario Veterinary College.