Thiamine Deficiency / Polioencephalomalacia

Polioencephalomalacia, commonly referred to as PEM or polio, represents one of the most important neurological conditions affecting cattle and sheep in modern livestock production systems. This condition results from a functional thiamine deficiency in the brain, leading to necrosis of the cerebral cortex and characteristic neurological signs that range from blindness and depression to severe convulsions and death. The name polioencephalomalacia derives from Greek roots meaning gray matter softening, describing the pathological changes observed in the cerebral cortex of affected animals. While true dietary thiamine deficiency is rare in ruminants due to rumen microbial synthesis of B vitamins, several mechanisms can induce functional thiamine deficiency, making this a complex condition with multiple potential causes.

Polioencephalomalacia primarily affects cattle and sheep, with occasional cases reported in goats and other ruminants. The condition occurs most frequently in young, growing animals on high-concentrate diets, making feedlot cattle and intensively fed lambs particularly susceptible. However, PEM can occur in grazing animals under certain circumstances, including consumption of thiaminase-containing plants or high-sulfur water sources. The prevalence varies considerably based on feeding practices and environmental factors, with some feedlot operations experiencing sporadic cases while others may see outbreak patterns when precipitating factors align. The condition remains a significant concern for beef and sheep producers due to its rapid onset, serious neurological consequences, and potential for mortality.

The economic and welfare impact of polioencephalomalacia can be substantial, particularly when multiple animals are affected. Death losses in untreated or late-treated cases often exceed fifty percent, representing significant economic loss in valuable feeder cattle or breeding stock. Animals that survive may have permanent neurological deficits that affect their productivity and market value. The welfare implications are severe, as affected animals experience progressive neurological dysfunction including apparent blindness, disorientation, and painful seizure activity. The dramatic clinical presentation creates distress for producers and caregivers witnessing the condition. Prevention and early intervention are essential to minimize both economic and welfare impacts.

The positive aspect of polioencephalomalacia is that it responds dramatically to early thiamine treatment, with many animals showing remarkable improvement within hours when therapy is initiated before severe brain damage occurs. Understanding the risk factors that predispose to PEM allows producers to implement management strategies that minimize occurrence. Recognition of early clinical signs enables prompt treatment that can be curative in many cases. Advances in understanding the relationship between sulfur intake and PEM have provided new insights into prevention, particularly in areas where high-sulfur water or feed ingredients contribute to disease occurrence.

The primary causes of polioencephalomalacia in ruminants involve disruption of thiamine availability or utilization in the brain, occurring through several distinct mechanisms. The classic cause involves production of thiaminase enzymes by certain rumen microorganisms, particularly Bacillus thiaminolyticus and Clostridium sporogenes, which destroy thiamine in the rumen before it can be absorbed. These thiaminase-producing bacteria proliferate when rumen conditions change, particularly with high-carbohydrate, low-fiber diets that cause rumen acidosis. A second major cause involves excessive sulfur intake, which leads to production of hydrogen sulfide and other sulfur compounds in the rumen that either destroy thiamine or interfere with its function in brain metabolism. High-sulfur feeds, water, or molasses blocks have been implicated in numerous PEM outbreaks.

Genetic predisposition does not play a significant role in polioencephalomalacia susceptibility, as this is fundamentally a nutritional and metabolic condition. However, certain management and feeding practices that vary between operations affect the likelihood of PEM development. Animals with ruminal dysfunction from other causes may be predisposed due to altered microbial populations. Individual variation in rumen microbial ecology could theoretically affect thiaminase production, though this has not been clearly demonstrated. The primary determinants of PEM risk relate to diet composition and management rather than animal genetics.

Environmental and management factors represent the most important determinants of polioencephalomalacia occurrence. High-concentrate diets with limited effective fiber create rumen conditions favorable for thiaminase-producing bacteria and may directly reduce thiamine synthesis by beneficial rumen organisms. Abrupt diet changes that disturb rumen microbial populations increase risk. Sulfur content of feed and water is increasingly recognized as a major risk factor, with total dietary sulfur exceeding 0.4 percent of dry matter posing significant risk. High-sulfur feed ingredients include distillers grains, corn gluten feed, and certain other byproduct feeds. Geographic areas with high-sulfur groundwater face endemic PEM risk. Consumption of thiaminase-containing plants, including bracken fern and certain other species, can induce PEM in grazing animals.

Risk factors for polioencephalomalacia development cluster around age, diet, and management circumstances. Young cattle and sheep between three months and two years of age face highest risk, particularly when transitioning to high-concentrate finishing diets. Feedlot placement is a high-risk period due to diet changes and stress. Hot weather may increase risk by concentrating sulfur in water sources or promoting hydrogen sulfide production in the rumen. Animals recently treated with antibiotics may have altered rumen microbial populations. Stress from transportation, weaning, or concurrent illness may predispose to PEM. Access to high-sulfur water sources during drought conditions has precipitated numerous outbreaks.

The pathophysiology of polioencephalomalacia centers on thiamine's essential role in brain energy metabolism and the consequences of its deficiency. Thiamine serves as a cofactor for several enzymes critical to glucose metabolism, including transketolase and pyruvate dehydrogenase. The brain relies almost exclusively on glucose for energy and has minimal thiamine storage capacity, making it uniquely vulnerable to thiamine deficiency. When thiamine becomes limiting, brain cells cannot generate adequate energy, leading to cellular dysfunction and death. The cerebral cortex, with its high metabolic demands, is most severely affected. Cerebral edema develops early due to failure of energy-dependent ion pumps, followed by neuronal necrosis if thiamine is not restored. Sulfur-induced PEM may involve additional mechanisms including direct toxicity of hydrogen sulfide to brain tissue.

Early warning signs of polioencephalomalacia may be subtle and easily missed without careful observation of affected animals. Initial signs often include separation from the herd or flock, with affected animals standing apart and appearing disoriented or confused. Mild depression and reduced feed intake frequently precede more obvious neurological signs by hours to days. Animals may seem to stare blankly or not recognize their surroundings. Subtle incoordination, particularly in the hindquarters, may be noted during movement. These early signs are critically important because treatment at this stage carries the best prognosis, yet they may be attributed to other causes or simply overlooked in large groups of animals.

Common symptoms of polioencephalomalacia are dominated by neurological dysfunction reflecting cerebral cortical damage. Blindness is one of the most characteristic signs, with affected animals failing to respond to visual threats or navigate around obstacles despite having normal pupillary reflexes. The classic stargazing posture involves the animal standing with its head elevated and nose pointed upward, apparently unaware of its surroundings. Cattle may press their heads against fixed objects such as fences, feedbunks, or walls. Circling or aimless wandering reflects disorientation. Muscle tremors, particularly of the face and ears, occur frequently. Teeth grinding indicates discomfort or neurological irritation. These signs may develop over hours to days depending on the severity and cause.

Behavioral changes in animals with polioencephalomalacia reflect the progressive loss of normal brain function. Affected animals become increasingly detached from their environment and fail to respond normally to handlers or herdmates. Normal flight responses are diminished or absent, and animals may allow close approach that they would normally avoid. Feeding and drinking behaviors cease as the condition progresses. Animals may vocalize abnormally or repeatedly. Social interactions with other animals become absent. The behavioral changes reflect the fundamental disconnection between the animal and its environment caused by cortical dysfunction.

Physical signs of polioencephalomalacia progress from subtle to dramatic as cerebral damage advances. The menace response, in which an animal should blink when a hand is thrust toward its eye, is absent in blind PEM cases while pupillary light reflexes remain intact, indicating that the visual cortex rather than the eye is affected. Opisthotonos, a rigid arching of the head and neck backward, develops in more severe cases. Nystagmus, an involuntary rhythmic movement of the eyes, may be observed. Strabismus, where the eyes deviate from normal parallel alignment, sometimes occurs. Hypersensitivity to stimuli may be present, with exaggerated responses to touch or sound. Gait abnormalities progress from mild ataxia to complete inability to stand.

Symptom progression in untreated polioencephalomalacia follows a characteristic pattern toward increasing neurological compromise. Early signs of depression and apparent blindness give way to increasingly obvious abnormal postures and behaviors. Stargazing becomes more pronounced and sustained. Head pressing against objects becomes persistent. Recumbency develops, initially with the animal able to maintain sternal position but eventually progressing to lateral recumbency with inability to right itself. Convulsions typically begin as tonic-clonic seizures that may be triggered by stimulation or occur spontaneously. Seizure frequency and severity increase as the condition progresses. Body temperature often elevates due to muscular activity during seizures. Without treatment, progression to coma and death occurs over hours to days.

Emergency symptoms requiring immediate veterinary intervention include active seizure activity, prolonged recumbency, severely abnormal mentation, and rapidly deteriorating neurological status. Animals in active convulsion require treatment to control seizure activity and prevent injury. Recumbent animals with opisthotonos face immediate risk of death. High fever from prolonged seizure activity indicates a critical condition. Animals found down with minimal response to stimulation may still respond to emergency thiamine treatment if administered immediately. Any animal showing neurological signs compatible with PEM should receive presumptive thiamine treatment without waiting for diagnostic confirmation, as early treatment dramatically improves survival.

Clinical examination for suspected polioencephalomalacia focuses on neurological assessment and identification of characteristic findings. The veterinarian evaluates mentation, noting the level of awareness and responsiveness to environmental stimuli. Visual function is tested through the menace response, obstacle navigation, and tracking of moving objects. Pupillary light reflexes are checked to confirm that blindness is cortical rather than ocular in origin. Gait is assessed for ataxia and other abnormalities if the animal is ambulatory. Cranial nerve function is evaluated systematically. Head position, presence of opisthotonos, and evidence of head pressing are noted. History regarding diet, recent changes, and sulfur intake sources is gathered to assess risk factors.

Diagnostic tests for polioencephalomalacia often confirm the diagnosis retrospectively, as treatment should not be delayed for diagnostic confirmation. Blood thiamine levels or transketolase activity can document thiamine status, but results may not be available rapidly enough to guide emergency treatment. Blood and rumen sulfur or sulfide concentrations help identify sulfur-induced cases. Cerebrospinal fluid analysis may show elevated protein but is nonspecific. The most dramatic diagnostic tool is the response to thiamine treatment, with significant improvement within six to twenty-four hours providing strong supportive evidence for the diagnosis. Necropsy examination of animals that die reveals characteristic bilateral cerebral cortical necrosis, and affected brain tissue fluoresces under ultraviolet light due to accumulation of fluorescent compounds.

Differential diagnosis for polioencephalomalacia must consider other neurological conditions affecting cattle and sheep. Lead poisoning produces similar neurological signs and should be considered in animals with potential exposure to lead-containing materials. Nervous coccidiosis causes neurological signs in calves, usually accompanied by diarrhea. Listeriosis causes cranial nerve deficits and circling, typically with a fever. Rabies must always be considered in neurological cases, particularly in endemic areas. Nervous ketosis in cattle produces neurological signs but occurs in recently calved cows. Salt poisoning or water deprivation causes cerebral edema and seizures. Bovine spongiform encephalopathy requires consideration in appropriate geographic regions. Trauma to the head can cause signs resembling PEM.

Herd-level diagnostics become important when multiple animals develop polioencephalomalacia or when investigating predisposing factors. Analysis of the total dietary sulfur content, including all feed ingredients and water, identifies potential sulfur toxicity. Feed analysis documents energy, fiber, and other nutritional parameters relevant to PEM risk. Water testing for sulfur, particularly sulfate concentration, is essential in endemic areas. Review of feeding management identifies practices that might promote thiaminase production or sulfur intake. Examination of remaining animals in the affected group may identify others with early or subclinical signs requiring treatment. Investigation of recent management changes helps identify precipitating factors.

Emergency treatment of polioencephalomalacia requires immediate administration of thiamine, as delays of even hours can mean the difference between recovery and death or permanent disability. Thiamine hydrochloride should be administered intravenously at a dose of ten to twenty milligrams per kilogram body weight, given slowly to avoid cardiovascular side effects. Intramuscular injection can be used if intravenous access is not immediately possible, though absorption is slower. Animals with active seizures require additional treatment to control convulsions, typically using diazepam or other benzodiazepines. Dexamethasone or other corticosteroids are commonly administered to reduce cerebral edema. Animals should be protected from injury during convulsions through soft bedding and removal of hazardous objects. Recumbent animals need to be positioned to maintain an open airway.

Medical management following initial stabilization continues thiamine supplementation and supportive care. Thiamine should be repeated every six to eight hours for the first twenty-four to forty-eight hours, as brain thiamine stores remain depleted and ongoing supplementation is necessary for recovery. Subsequent doses can be given intramuscularly once the animal has stabilized. Continuation of thiamine treatment three to four times daily for three to five days ensures complete restoration of brain thiamine status. Anti-inflammatory medications including corticosteroids are often continued for the first few days to manage cerebral edema. Anticonvulsant medication may be needed if seizures recur. Note that withdrawal times apply to corticosteroids and should be observed for animals destined for slaughter.

Surgical intervention is not applicable for polioencephalomalacia, as this is a metabolic and nutritional condition affecting the brain that requires medical rather than surgical treatment. No surgical procedures address the underlying brain pathology. Supportive surgical procedures such as tube feeding might be indicated for animals unable to eat normally during recovery, but these address secondary supportive needs rather than the primary condition. Emergency placement of intravenous catheters facilitates repeated medication administration but is a supportive technique rather than definitive surgery.

Supportive care plays a crucial role in successful treatment outcomes for polioencephalomalacia cases. Recumbent animals require deep, soft bedding to prevent pressure sores, with regular repositioning every few hours to minimize complications. Protection from environmental extremes including heat, cold, and precipitation is essential. Fluid therapy may be indicated for animals unable to drink normally or those with increased fluid requirements from seizure activity and hyperthermia. Nutritional support through tube feeding may be necessary for animals that cannot eat. Eye protection prevents corneal injury in blind animals. Quiet, low-stimulus environments reduce triggers for seizure activity. Nursing care continues until the animal has recovered sufficiently to care for itself.

Herd treatment protocols address the population when multiple cases occur or when risk factors are identified in the group. Other animals in the affected group should be monitored closely for early signs of PEM and treated promptly if symptoms develop. The diet should be evaluated and modified to reduce PEM risk, including reducing sulfur content and ensuring adequate effective fiber. Water sources should be tested and changed if sulfur content is excessive. Thiamine supplementation of the herd through injectable products, water supplementation, or feed additives may be considered during outbreak situations. Management changes to reduce rumen acidosis and thiaminase production protect the remaining at-risk population.

Treatment decisions consider the prognosis based on disease severity and duration before treatment. Animals treated very early in the disease course, before recumbency develops, have excellent prognosis with appropriate therapy and may recover completely within twenty-four to forty-eight hours. Those treated after convulsions begin have more guarded prognosis but may still recover with aggressive treatment. Animals that have been recumbent and seizing for extended periods before treatment face poor prognosis and may have permanent neurological damage even with treatment. Economic value of the animal influences treatment intensity decisions, though humane considerations require appropriate pain management and euthanasia if prognosis is hopeless.

Recovery timeline for polioencephalomalacia varies dramatically based on the severity of disease at presentation and the promptness of treatment. Animals treated at the earliest sign of blindness and depression may show improvement within hours and recover completely within one to three days. Those treated after developing recumbency but before prolonged seizures typically require three to seven days for significant improvement and may need two to three weeks for full recovery. Severely affected animals with extended seizure activity before treatment may require weeks to months for recovery, if it occurs, and many retain permanent neurological deficits. Some animals never recover adequate function and require euthanasia on welfare grounds.

Post-treatment care and monitoring support the recovering animal through the convalescent period. Thiamine supplementation should continue for several days even after clinical improvement to ensure brain stores are fully replenished. Animals should be kept in safe environments where blindness or incoordination does not pose injury risk. Feed and water should be easily accessible without requiring visual navigation. Monitoring for recurrence of neurological signs identifies animals that need additional treatment or have developed complications. Body condition should be maintained through the recovery period with appropriate nutritional support. Social isolation may be necessary initially to prevent injury from herdmates.

Prognosis factors influencing recovery outcomes center on the extent of brain damage at the time treatment is initiated. Animals treated within the first twenty-four hours of clinical signs before significant cortical necrosis develops carry good to excellent prognosis. Those treated within twenty-four to forty-eight hours have fair to guarded prognosis, with outcomes depending on individual response. Animals treated after prolonged illness with severe seizures have poor prognosis, and survivors often have permanent blindness, behavioral changes, or other neurological deficits. The speed and completeness of initial response to thiamine treatment provides prognostic information, with rapid improvement indicating better long-term outcomes.

Return to production considerations for recovered animals depend on the completeness of neurological recovery. Animals that recover completely with normal vision and behavior can return to their intended production use without restriction, though withdrawal periods for any medications used must be observed before slaughter. Those with persistent blindness are at significant disadvantage in most production settings and may be best suited for immediate marketing after withdrawal periods. Animals with residual behavioral abnormalities may not perform normally and present ongoing management challenges. Breeding animals that recover may reproduce normally but should be monitored for any performance deficits. The underlying cause of PEM should be corrected before recovered animals return to the same management conditions.

Vaccination is not applicable for polioencephalomalacia, as this is a nutritional and metabolic condition rather than an infectious disease. However, preventive management practices can substantially reduce PEM occurrence in at-risk populations. Thiamine supplementation of cattle and sheep diets can provide insurance against marginal thiamine status, particularly during high-risk periods such as feedlot entry or during known sulfur exposure. Injectable thiamine can be administered prophylactically to individual high-value animals during high-risk periods. Vitamin B complex supplementation in stressed animals provides thiamine along with other B vitamins that support overall metabolic function.

Biosecurity measures for polioencephalomalacia prevention focus on controlling dietary risk factors rather than preventing pathogen transmission. Evaluation of all feed ingredients for sulfur content prevents unknowing introduction of high-sulfur feeds. Testing of water sources, particularly new wells or during drought conditions, identifies high-sulfur water before animals are exposed. Documentation of total dietary sulfur allows assessment of PEM risk with different ration formulations. Quarantine in the traditional sense is not applicable, but gradual diet transitions for incoming animals reduce rumen upset that contributes to PEM risk.

Nutritional prevention through careful diet formulation represents the cornerstone of PEM prevention in intensive production systems. Total dietary sulfur should be maintained below 0.4 percent of dry matter, and ideally below 0.3 percent, with attention to all sources including feed, water, and supplements. Adequate effective fiber in the diet promotes healthy rumen function and reduces conditions favoring thiaminase-producing bacteria. Gradual diet transitions over two to three weeks allow rumen microbial populations to adapt without excessive disruption. Avoiding abrupt increases in concentrate feeding prevents acidosis that predisposes to PEM. Thiamine supplementation of high-risk rations provides additional protection.

Management practices supporting PEM prevention extend beyond diet composition to encompass overall animal handling and health management. Minimizing stress through appropriate handling, transportation practices, and stocking densities reduces metabolic demands and PEM susceptibility. Ensuring constant access to clean, low-sulfur water prevents sulfur toxicity and dehydration. Processing and handling facilities that minimize stress reduce the overall physiological burden on animals. Heat stress management through shade, ventilation, and water access is important in hot environments. Avoiding thiaminase-containing plants in pastures and hay prevents plant-induced thiamine destruction.

Quarantine and testing protocols for PEM prevention focus on identifying and managing dietary risk factors. New feed ingredients, particularly byproducts, should be tested for sulfur content before incorporation into rations. Water testing should be performed on any new water sources and repeated periodically, particularly during drought when water quality may change. Animals from different dietary backgrounds should be transitioned gradually to new rations. Monitoring of animal health and behavior identifies early PEM cases that indicate the need for population-level intervention. Documentation of all diet changes and associated health outcomes builds knowledge for future PEM prevention.

Daily management and monitoring for polioencephalomalacia prevention requires attention to both individual animals and population-level risk factors. Daily observation of animals should include assessment of behavior, mentation, and any signs of visual impairment or neurological abnormality. Animals that separate from the group, appear disoriented, or show abnormal postures warrant closer examination. Feed intake monitoring identifies animals going off feed, which may precede PEM development. Water consumption should be monitored, particularly in hot weather when changes in water source or concentration might occur. Staff should be trained to recognize early PEM signs and understand the urgency of prompt treatment.

Housing and environmental management considerations for PEM prevention center on maintaining consistent, appropriate dietary management. Feed delivery systems should ensure uniform diet distribution so that individual animals do not receive excessive concentrate or inadequate fiber. Water systems should provide adequate clean, low-sulfur water at all times. Heat abatement through shade, sprinklers, or ventilation reduces stress that may contribute to PEM susceptibility. Facility design should minimize stress during handling and processing. Pen conditions should prevent animals from consuming unusual materials that might affect rumen function or provide sulfur sources.

Herd health programs addressing polioencephalomalacia incorporate PEM prevention into comprehensive health and nutrition management. Working with veterinarians and nutritionists to formulate rations that minimize PEM risk while meeting production goals requires balancing multiple considerations. Establishing sulfur limits for total diet and monitoring compliance ensures that PEM risk remains acceptable. Regular water testing, particularly in endemic areas, identifies problems before clinical disease occurs. Processing protocols for incoming animals should include PEM prevention considerations. Training programs ensure that all staff recognize PEM signs and understand treatment urgency.

Record keeping and monitoring provide the information needed to evaluate PEM risk and respond to cases effectively. Documentation of all PEM cases including date, animal identification, clinical signs, treatment, and outcome allows analysis of patterns and risk factors. Feed records including ingredient sources and analysis results support investigation of cases. Water testing results should be maintained for reference. Treatment protocols and outcomes inform future case management. Production data may reveal subtle associations between management factors and PEM occurrence that guide prevention efforts.

Economic considerations for PEM prevention and management demonstrate the value of proactive risk reduction. Death losses from PEM can be substantial, with individual feeder cattle worth hundreds to thousands of dollars. Treatment costs including veterinary fees, medications, and labor add to direct losses. Production losses in affected animals that survive reduce returns. Prevention costs including appropriate diet formulation, water testing, and management attention are modest compared to disease costs. Cost-benefit analysis strongly favors investment in prevention, particularly in operations or areas with known PEM risk. The value of early detection and treatment cannot be overstated, as prompt intervention dramatically improves outcomes.

High-risk breeds and species for polioencephalomalacia are determined primarily by management system and diet rather than inherent breed susceptibility. Cattle and sheep are the primary species affected, with cattle accounting for most reported cases in modern production systems. Within cattle, no breed appears inherently more susceptible, but beef breeds in feedlot finishing programs face high risk due to typical high-concentrate diets. Dairy heifers on accelerated growth programs may develop PEM. Among sheep, feedlot lambs and intensively finished market lambs face greatest risk. Goats can develop PEM but cases are less commonly reported. All ruminants consuming high-concentrate, low-fiber diets with elevated sulfur intake face potential PEM risk.

Production type considerations significantly influence polioencephalomalacia risk within species. Feedlot cattle on high-energy finishing rations represent the highest-risk population due to typical diet composition and management. Cattle receiving distillers grains or other high-sulfur byproducts face elevated risk based on sulfur intake. Stocker cattle transitioning from grass to grain during backgrounding are at risk during the adaptation period. Dairy cattle are less commonly affected because dairy rations typically contain more fiber, but high-producing cows on aggressive nutrition programs can develop PEM. Sheep in feedlot finishing or on intensive concentrate supplementation face similar risks to feedlot cattle. Grazing animals can develop PEM from thiaminase-containing plants or high-sulfur water but are overall at lower risk than intensively fed animals.

Genetic selection and testing considerations for polioencephalomalacia are limited because this is an environmentally induced condition rather than a genetic disorder. No genetic tests predict PEM susceptibility, and no breeding programs select for or against PEM resistance. Individual variation in rumen microbial ecology could theoretically influence thiaminase production, but this is not practically measurable or selectable. Management of dietary and environmental risk factors rather than genetic selection remains the appropriate approach to PEM prevention. Animals that have recovered from PEM do not appear to have increased susceptibility to future episodes if the underlying cause is corrected.

Commonly co-occurring conditions with polioencephalomalacia often relate to the same dietary circumstances that induce PEM. Rumen acidosis frequently precedes or accompanies PEM in feedlot cattle, as the same high-concentrate diets promote both conditions. Liver abscesses, another consequence of aggressive feedlot nutrition, may occur in the same populations at risk for PEM. Sulfur-induced PEM cases may see concurrent respiratory effects from hydrogen sulfide inhalation in enclosed or poorly ventilated facilities. Trace mineral imbalances may coexist when overall mineral nutrition is poorly managed. Digestive upset and reduced feed intake often precede PEM development and may indicate early rumen dysfunction.

Conditions with similar symptoms to polioencephalomalacia require careful differentiation for appropriate treatment. Lead poisoning produces nearly identical neurological signs including blindness, head pressing, and seizures, making assessment of potential lead exposure critical. Listeriosis causes circling, head tilt, and cranial nerve deficits but typically involves fever and less symmetric presentations. Rabies must be considered in any neurological case in endemic areas, requiring appropriate precautions during examination. Nervous coccidiosis affects calves and includes diarrhea along with neurological signs. Salt poisoning or water deprivation causes cerebral edema with seizures but has a distinct history. Bovine spongiform encephalopathy and other prion diseases cause progressive neurological signs but over longer timeframes.

Complications and sequelae of polioencephalomalacia extend beyond the acute neurological disease. Aspiration pneumonia may develop when dysphagia or recumbency leads to inhalation of rumen contents. Injuries sustained during seizures or while disoriented include fractures, lacerations, and soft tissue trauma. Pressure sores develop in recumbent animals that survive the acute phase. Permanent blindness affects some recovered animals, particularly those with delayed treatment. Residual behavioral abnormalities including abnormal responsiveness and impaired learning may persist. Secondary metabolic derangements from prolonged recumbency include muscle damage and kidney injury. Long-term productivity may be reduced even in animals that appear to recover clinically.