Bovine Traumatic Nervous System Injuries – NAVLE Study Guide

Overview and Clinical Importance

Traumatic nervous system injuries represent a significant cause of morbidity, mortality, and economic loss in cattle production. These injuries encompass damage to the spinal cord, peripheral nerves, and brain resulting from mechanical trauma. The periparturient period is a particularly high-risk time for cattle, with calving paralysis being one of the most commonly encountered traumatic nerve conditions. Understanding the neuroanatomy, clinical presentation, diagnosis, and management of these injuries is essential for NAVLE success and clinical practice.

Traumatic nervous system injuries in cattle most commonly result from: dystocia and calving-related injuries, mounting behavior during estrus, falls and handling accidents, prolonged recumbency (downer cow syndrome), and improper restraint during procedures. Early recognition and intervention are critical, as delays beyond 6 hours significantly worsen prognosis due to secondary muscle and nerve damage.

Neuroanatomical Foundations

Spinal Cord Segments and Function

The bovine spinal cord is divided into functional regions that correspond to the innervation of specific body areas. Cattle have 7 cervical vertebrae (C1-C7), 13 thoracic vertebrae (T1-T13), 6 lumbar vertebrae (L1-L6), and 5 fused sacral vertebrae (S1-S5). Understanding these segments is crucial for lesion localization.

Spinal Cord Functional Regions

Key Peripheral Nerves of the Hindlimb

The lumbosacral plexus gives rise to the major nerves supplying the hindlimb. These nerves are particularly vulnerable to compression and stretching during dystocia. The anatomical location of each nerve determines its susceptibility to specific types of trauma.

Calving Paralysis (Parturient Paresis)

Pathophysiology

Calving paralysis is caused by excessive and prolonged intrapelvic pressure due to fetopelvic disproportion. A large fetus relative to the pelvic canal diameter places pressure on the sciatic and obturator nerves as they course along the pelvic inlet. The L6 nerve root, which contributes to both the sciatic and obturator nerves, is particularly vulnerable to compression.

The mechanism of nerve injury involves: sustained pressure exceeding 20 minutes causing localized ischemia, subsequent loss of nerve function (temporary or permanent), direct traumatic tearing or transection in severe cases, and secondary inflammatory changes with perineural edema.

Clinical Presentations by Nerve Affected

Sciatic Nerve Paralysis

Clinical Signs: Persistent knuckling of the fetlock (most characteristic sign), slight dropping of the hock, weight bearing variably affected with maintained stifle extension (femoral nerve intact), prominent patellar reflex due to loss of antagonism, decreased tail tone and anal sphincter tone in severe cases, possible atonic bladder, and analgesia of the hindlimb distal to the stifle (except craniomedial tibia).

Diagnostic Features: Bilateral involvement common in severe dystocia cases. Unilateral in milder cases. The knuckling is typically bilateral in severe cases and unilateral in milder presentations.

Obturator Nerve Paralysis

Clinical Signs: Inability to adduct the hindlimbs, base-wide stance, limbs splayed out (doing the splits), particularly problematic on slippery surfaces, able to bear weight when limbs positioned properly, and when sitting the hindlimbs are often extended forward.

Complications: Hyperextension of hindlimbs can lead to adductor muscle rupture and hip luxation. These secondary injuries significantly worsen prognosis.

Exam Focus: On the NAVLE, when you see a cow immediately post-calving with splayed hindlimbs that can bear weight when manually positioned, think OBTURATOR nerve paralysis. The classic presentation is a cow that can support weight but cannot adduct the limbs - key distinguishing feature from sciatic paralysis where weight bearing is compromised.

Peroneal (Fibular) Nerve Paralysis

Clinical Signs: Knuckling of the fetlock onto dorsal surface, hock appears overextended, ability to bear weight but digit cannot be extended, walking on dorsum of fetlock in severe cases, and decreased sensation on dorsal metatarsal area, fetlock, and digit.

Etiology: Most commonly caused by pressure ischemia over the lateral stifle region (lateral femoral condyle) during prolonged recumbency or parturition. The superficial location of this nerve makes it vulnerable to external compression.

Femoral Nerve Paralysis

Clinical Signs: Inability to extend the stifle joint or bear weight, affected leg appears to collapse, rapid atrophy of quadriceps femoris within 7-10 days, pelvis markedly tilted toward affected side in unilateral cases, and calves with bilateral involvement adopt a dog-sitting posture.

Common Cause: Most common in calves following dystocia with hip-lock and excessive traction on hindlimbs during posterior presentation.

Radial Nerve Paralysis (Forelimb)

Clinical Signs: Dropped elbow (proximal injury) or minimal elbow drop (distal injury), partial flexion of carpus and fetlock, inability to advance and extend the limb, limb dragging during ambulation, and skin analgesia on lateral aspect of leg.

Common Causes: Prolonged lateral recumbency on hard surfaces (tilt tables, concrete), casting with ropes, violent struggling against restraint, fractures of humerus, and aggressive behavior from other cattle.

Differentiating Nerve Injuries: Clinical Summary

Memory Aid - "SOFT" for Calving Paralysis Nerves: Sciatic (knuckling, most common), Obturator (splits/splaying), Femoral (stifle collapse), Tibial/peroneal (hock overextension). Remember: The L6 nerve root contributes to both sciatic AND obturator - damage here affects both!

Spinal Cord Trauma

Etiology and Pathophysiology

Acute spinal cord injuries in cattle are commonly associated with spinal fracture or luxation. Common causes include: mounting behavior during estrus (bulls and cows), being ridden by other cattle in feedlots, bulls fighting, calves stepped on by adult cattle, falls during handling or transport, pathological fractures secondary to malnutrition or vertebral osteomyelitis, and improper restraint in chutes or handling facilities.

Secondary Injury Cascade: Damage to the spinal cord is caused not only by primary mechanical injury but also by secondary pathological changes including edema, hemorrhage, demyelination, and necrosis. These secondary changes result from biochemical factors including the release of free radicals, leukotrienes, and prostaglandins that cause further injury to nervous tissue and compromise blood flow to the spinal cord.

Clinical Signs of Spinal Trauma

Clinical signs of spinal trauma are typically acute and may progress with unstable fractures or luxations. Signs include: bilateral knuckling of the lower hindlimbs, staggering gait with tendency to fall when turning or running, inability to stand or walk, tail paralysis and flaccidity (caudal lesions), urinary and fecal incontinence, and variable degrees of ataxia and paresis depending on lesion severity and location.

Diagnosis

Neurological Examination: A systematic neurological examination should assess: mentation and behavior, gait observation (ataxia, paresis, circling), postural reactions including proprioceptive positioning and sway response, spinal reflexes (patellar, withdrawal, panniculus), assessment of deep pain perception caudal to suspected lesion, and evaluation of tail tone, anal sphincter tone, and bladder function.

Diagnostic Imaging: Radiographs usually demonstrate vertebral fractures and luxations. However, approximately 25% of spinal fractures may be missed on radiographs alone. Myelography can be an effective diagnostic test in adult cattle to evaluate spinal cord compression. Advanced imaging (CT, MRI) when available provides superior detail but is limited by patient size and availability.

Downer Cow Syndrome and Secondary Recumbency

Definition and Pathophysiology

Bovine secondary recumbency (downer cow syndrome) is a complication of primary recumbency of greater than 24 hours duration that was not treated or was unsuccessfully treated, resulting in an inability to rise or stand due to secondary muscle and nerve damage. The initial cause may be traumatic, metabolic, infectious, or toxic.

Secondary Complications: Compartment syndrome occurs when mechanical constriction of venous drainage leads to ischemic muscle and nerve necrosis. Crush syndrome develops when muscle breakdown releases myoglobin (causing potential renal failure) and potassium (causing potential cardiac arrhythmias). Pressure neuropathy damages the peroneal, sciatic, and radial nerves. Muscle and tendon rupture, particularly the gastrocnemius, may occur during struggling.

Clinical Assessment of Downer Cattle

Assessment should include: complete physical examination ruling out fractures, metabolic disease (hypocalcemia, hypokalemia), and infectious causes. Evaluate hindlimb position noting splayed limbs (suggests obturator involvement) and extended upper limb with skin crease (suggests fracture). Assess alertness and appetite, presence or absence of effort to rise, and check for decubital ulcers, mastitis, and signs of dehydration.

Prognostic Indicators

Treatment and Management

Calving Paralysis Treatment

Essential Nursing Care Protocol

Positioning: Lateral recumbency must be IMMEDIATELY corrected to prevent bloating, regurgitation, aspiration of gastric contents, and pressure lesions to brachial plexus and radial nerve. Roll cow into sternal recumbency. To maintain this posture, draw the limb the cow was lying on from under the body (e.g., if lying on left side, roll into sternal recumbency on right side). Support under shoulder with straw bales if needed.

Environmental Protection: Rain and wind can reduce body temperature and worsen shock. Provide windbreak of straw bales, straw bedding for insulation from ground, and shelter in cold weather. Recumbent cattle do not require a warm environment but can gradually succumb to hypothermia without protection.

Daily Attempts to Rise: Make daily attempts to bring cow to feet. Apply sharp pressure with knees to muscle mass below and caudal to scapula (NOT on ribs - fracture risk). Assistant lifts root of tailhead with both hands. Hip clamps controversial - require experience and can cause trauma if used improperly. Canvas sling under sternum essential for consistent success as forelimbs support 60% of body weight.

Memory Aid - Downer Cow "6-24-33" Rule: 6 hours = time before irreversible damage begins, 24 hours = threshold for secondary recumbency diagnosis, 33% = recovery rate if down greater than 24 hours. Roll every 6 hours, treat before 6 hours, and prognosis drops after 24 hours!

Euthanasia Considerations

Euthanasia should be considered when: cow becomes listless with no interest in feed, decubital lesions develop, condition deteriorates despite treatment, owner unable or unwilling to provide required nursing care, severe fractures present, or animal has lost deep pain perception caudal to lesion. A cow with decubital lesions, poor appetite, or wasting is unsuitable for salvage slaughter. Attempting to transport recumbent animals except for veterinary care is illegal in many countries and considered an act of cruelty.

Prevention Strategies

Calving Management: Avoid prolonged second stage labor. Limit excessive traction during calf delivery. Two people pulling should extend both foreleg fetlocks one hand's breadth beyond vulva within 10 minutes - greater traction needed forewarns of hip-lock risk. Avoid calving cows standing in stocks (risk of cow falling with calf halfway out).

Facility Design: Maintain properly repaired corral systems appropriate for cattle of various sizes. Provide adequate footing - concrete should be grooved or covered with rubber matting. Avoid gaps under gates where cattle may attempt to escape. Pad surfaces for cattle in lateral recumbency during procedures.

Metabolic Disease Prevention: Prevent hypocalcemia (milk fever) - 38% of downer cows have milk fever as primary cause. Cows treated for milk fever within 6 hours have only 2% downer rate, versus greater than 25% if treated at 7-12 hours, and nearly 50% if treatment delayed beyond 18 hours.