Overview of Bovine Secondary Recumbency
(Downer cow syndrome)
Recumbency in cattle is caused by numerous metabolic, traumatic, infectious, degenerative, and toxic disorders. If treatment of the underlying cause of recumbency is not successful and cattle are unable to rise for >24 hr after initial recumbency, they may develop a secondary recumbency from pressure damage to muscles and nerves, often termed “downer cow syndrome.” An alert downer cow does not show signs of systemic illness or depression, is able to eat and drink, and remains in sternal recumbency for no apparent reason. A nonalert downer cow appears systemically sick and depressed. Downer cow syndrome also describes the pathology of pressure-induced muscle and nerve injuries after prolonged recumbency. The most important pathophysiologic event that develops during prolonged recumbency is a pressure-induced ischemic necrosis of the thigh muscles that frequently affects both hindlegs.
Nonambulatory disabled livestock are those that cannot rise from a recumbent position or that cannot walk. This includes, but is not limited to, those with broken appendages, severed tendons or ligaments, nerve paralysis, a fractured vertebral column, or metabolic conditions. Downer cows have been categorized according to potential diseases of the CNS into nonambulatory cows with progressive or nonprogressive neurologic findings.
In most cases, downer cow syndrome is a complication of periparturient hypocalcemia (milk fever, see Parturient Paresis in Cows) in cows that do not fully respond to calcium therapy. Calving paralysis after dystocia may also result in recumbency due to traumatic injury to tissues and nerves inside the pelvic cavity. Regardless of the initial cause of recumbency, all cattle develop pressure-induced damage to muscles and nerves of the pelvic limbs, especially when lying on a hard surface. The hindlimb muscles of the leg the animal is lying on are compressed between the bones and the skin by the physical pressure from the weight of the recumbent cow.
With prolonged recumbency (eg, if treatment of hypocalcemia is delayed), the lymphatic and venous drainage to muscle is decreased because of sustained pressure with no decrease in arterial blood flow. The net result of pressure-induced changes in blood flow is an increase in interstitial fluid volume and pressure within the muscle, because the fascia around each muscle cannot expand sufficiently to accommodate the increase in interstitial volume. In severe and prolonged cases of recumbency, the increase in intramuscular pressure is visible as a firm swelling of the muscle. The resulting compression of muscles, nerves, and blood vessels within an enclosed compartment induces ischemic pressure damage of muscle and nerves, also named compartment syndrome. The severity of pressure damage to the muscles depends on regional anatomic factors (bones), duration of compression, and the surface on which the animal is kept.
Pressure myopathy in downer cows is often complicated by damage to and functional loss of the sciatic nerve and its peroneal branch. The sciatic nerve may be damaged by direct compression against the caudal femur, secondary swelling of the surrounding muscles, or both. The degree of damage to the sciatic nerve is thought to be a critical factor for recovery of downer cows. Damage to the peroneal branch of the sciatic nerve results from direct pressure on the nerve as it crosses over the lateral condyle of the femur.
Experimental sternal recumbency in halothane-anesthetized cattle for 6–12 hr, with the right hindlimb positioned under the body, resulted in a swollen and rigid limb and permanent (terminal) recumbency in 50% of the cases. Cattle able to stand after anesthesia showed hyperflexion of the fetlock, indicating peroneal nerve paralysis, and myoglobinuria with dark brown urine. Necropsy of terminal downer cases revealed extensive necrosis of the caudal thigh muscles and inflammation of the sciatic nerve caudal to the proximal end of the femur.
Additional complications of prolonged recumbency include acute mastitis, decubital ulcers, and traumatic injuries to the limbs (eg, laceration and rupture of muscle fibers in the thigh) from struggling and efforts to rise.
Periparturient cows may be found in lateral recumbency, which may indicate an unresolved metabolic problem such as hypocalcemia or hypomagnesemia. Inquiries into the severity and duration of parturition may suggest that the recumbency is at least partially due to exhaustion. In involuntary sternal recumbency, some cows may have a dull, listless appearance. This may indicate hypocalcemia in periparturient mature cows. The second most likely cause of depression is toxemia, the cause of which is most commonly found in the genital tract or mammary gland. Other cows found in involuntary sternal recumbency may be bright and alert in appearance—the most typical demeanor of the true problem downer cow. If the animal is young or not pregnant, the cause is likely to be either physical damage or a rare condition, either of which requires careful, detailed examination.
The environment of the animal can have a bearing on the cause. If the footing is slippery, physical damage to the musculoskeletal system should be suspected. This is much less likely among cows in open space with a dirt or well-bedded surface.
The positioning of the hindlimbs may indicate the cause of the recumbency. Limbs splayed out behind the animal may indicate obturator nerve paresis or paralysis, hip dislocation, or fracture of the femur or tibia. Fracture should be suspected whenever the upper limb is extended sideways in such a manner that a crease is formed in the skin.
A thorough physical examination should be performed when the cow is first presented. The rectal temperature should be within the normal range. If it is lower than normal, some level of shock might be present. Recession of the eyes into the orbit or persistence of a skin fold for >2 sec indicates dehydration. Pallor of the mucous membranes suggests toxemia, in which case a weak pulse and tachycardia may be present. The respiration of a recumbent cow may be labored by virtue of the pressure of the abdominal contents on the diaphragm.
Vaginal exploration is mandatory in every peripartum, recumbent cow and may lead to discovery of a decomposing fetus. Damage to and infection of the wall of the vagina is common. Metritis and an associated toxemia can contribute to postpartum recumbency.
Rectal exploration is essential for differential diagnosis. The degree of uterine involution should be appropriate for the number of days postpartum. Ballottement of fluid in the organ or lack of tonicity should be noted. Unexpected anomalies may be palpated. Adhesions, lumps of necrotic fat, and enlargement or turgidity of the cervix or vaginal wall are all sequelae of a difficult birth. Hip dislocations and fractures of the pelvis may be palpated per rectum, particularly if an assistant vigorously manipulates the upper limb of a cow in lateral recumbency. Movement of the head of the femur in the obturator foramen may also be detected in cattle with caudoventral hip dislocation. Craniodorsal dislocation of the hip, the most common direction for hip dislocation, or fracture of the femoral neck or proximal femur should be suspected if the affected limb appears shorter than the contralateral limb. Pelvic fractures can be associated with sciatic nerve paralysis, whereas hip dislocation may be associated with some degree of obturator nerve paralysis. If either condition is suspected, the sensory state of the limbs should be evaluated by judicious and humane application of an electric prod to the distal limb. Involuntary sternal recumbency may be associated with lymphosarcoma of the spinal canal, vertebral abscesses, or bizarre traumatic injuries.
Mammary gland examination should always be performed on recumbent cows. A toxic infection of the udder with an organism such as Escherichia coli can be a primary cause of recumbency. However, such an infection may be precipitated by the recumbency, especially if the udder is engorged and remains unmilked.
Blood samples are not usually taken when treating routine cases of hypocalcemia. However, hypocalcemia, hypophosphatemia, and hypokalemia should be assumed to be present in all recumbent cattle, and determination of the biochemical status of cattle unresponsive to calcium therapy frequently helps guide treatment and prognosis. Hypokalemia and hypophosphatemia are commonly quoted causes of creeper cows (cows able to crawl but unable to stand). Alert downer cows may have normal serum concentrations of calcium, potassium, magnesium, and phosphorus. Downer cows have increased serum CK, AST, and LDH; cows that do not recover have higher serum AST and CK activities than cows that do recover. Increased serum CK activity is a specific indicator of muscle damage; however, CK activity peaks shortly after the start of muscle damage and declines noticeably within 4 hr. For this reason, increased serum AST activity is the best prognostic indicator in recumbent cattle, with higher AST activities indicating a poorer prognosis. In cattle with severe muscle damage, the urine may contain myoglobin as well as higher than normal concentrations of protein. The age and mean serum concentrations of phosphorus, magnesium, sodium, bilirubin, glucose, and urea are not significantly different between recovering and nonrecovering cows.
Ischemic necrosis and rupture of muscles of the thigh region are common necropsy findings in downer cows. Hemorrhage and rupture of adductor muscles may be seen if the animal “spread-eagled” itself while struggling to rise on a slippery surface such as wet or icy concrete. Traumatic and inflammatory injuries to sciatic and peroneal nerves are also found in downer cows. Damage to intrapelvic nerves, such as the sciatic and obturator nerves, account for most cases. Decubital injuries to the lateral aspect of the stifle can be associated with damage to the peroneal nerve.
Downer cows are often hypocalcemic. If an apparently hypocalcemic cow does not respond to calcium therapy, potassium, phosphorus, and magnesium should be given as additional treatments pending results of laboratory tests. Monitoring blood mineral status is an important part of downer cow management.
In most cases, recovery depends on the quality of recumbency management and nursing care. Lateral recumbency must be corrected immediately to avoid regurgitation and inspiration of stomach contents. The animal should be rolled into sternal recumbency. However, if this posture is to be maintained, the limb on which the animal has been lying should be drawn from under the body. In other words, if the animal was presented in lateral recumbency on its left side, it should be rolled into sternal recumbency on its right side. Support (eg, straw bale) placed under the shoulder may be required for some animals to maintain sternal recumbency.
Attempting to stabilize a recumbent cow on a concrete surface is highly undesirable but sometimes unavoidable. Bedding the area around and under the cow with wet, sticky manure to a depth of >6 in. is a common practice. At least 10 in. of dry straw should be distributed over the wet mass. If the cow struggles and scrapes the wet manure, exposing concrete, more manure must be added. The manure pack provides good footing but also may soil the skin with urine and manure. Dermatitis can result, and cow comfort is reduced. More seriously, the risk of mastitis resulting from the contaminated environment is very high. A bed of sand >10 in. deep provides a more effective method to house a recumbent cow. A sand bed usually drains well, and good hygiene can be maintained if voided manure is removed several times a day.
Some recumbent cattle appear to lose interest in trying to stand; these cattle may benefit from use of a specially designed flotation tank that has a volume of ~2,500–3,000 L. Cattle are loaded into the flotation tank by being dragged on a mat into the empty tank. Doors are then put in place, and the tank is filled with lukewarm water. Cold or hot water should be avoided, because it can induce hypothermia or hyperthermia. Cattle should be encouraged to stand once the water reaches the level of the scapulohumeral joint. When the cow stands, the musculoskeletal and nervous systems should be thoroughly examined to identify underlying disease processes. Cattle that can support their own weight should be permitted to stand for 6–8 hr; however, the water in the tank should be removed as soon as cattle exhibit trembling. Cattle that remain standing should be encouraged to walk slowly from the tank on a nonslip surface. Cattle able to walk out of the tank after the first flotation treatment are 4.8 times more likely to survive than those that do not walk out of the tank. Cattle that stand on all four limbs during the first flotation treatment are 2.9 times more likely to survive than those that had an asymmetric stance or were unable to stand. Reported success rates in returning recumbent cattle to normal ambulation range from 37%–46%.
Hobbling may be considered in cows suspected to have obturator or sciatic nerve damage to prevent overabduction that can lead to muscular damage. Ropes should never be used for this purpose. A soft nylon strap may be wrapped twice around the middle of each metatarsus, allowing a distance of at least 3 ft between the legs.
On every day of the recumbency, an attempt should be made to bring the cow to its feet. Several simple but effective techniques can be tried. In one method, the clinician stands with feet pressed under the cow at a point below the scapulohumeral joint. A sharp blow is delivered by driving the knees into the muscle mass below and caudal to the scapula. This method must not be used on the thoracic wall unprotected by the muscle mass to avoid fracturing the ribs. If the animal struggles to rise, an assistant should grasp the root of the tail with both hands and lift. Lifting on any other part of the tail may cause damage. Recently calved cows can be motivated to rise if they hear their own calf bawling with hunger. The calf is best restrained close to the cow but out of her sight. Some workers use electric goads and various anecdotal or traditional methods of inflicting pain to stimulate a cow to rise; these measures have a low success rate in inexperienced hands and are not recommended.
The value of hip clamps is controversial. Their proper use requires experience, skill, and a delicate touch. Continual use causes trauma and pain that is counterproductive. The forelimbs support 60% of a cow’s weight and, therefore, the use of a canvas sling under the sternum is almost mandatory for consistent success. A chest band is required to prevent the sling from slipping backward. If the sling is suspended from the tine at one end of a fork lift, and the hip clamps from a tine at the other end, minimal trauma results. If a fork lift is not available, a T-bar suspended by a pulley from an overhead beam (or a tripod for animals at pasture) will serve. The jaws of the clamps must be well protected with synthetic foam or rubber secured in place with a wrap of duct tape.
Hip clamps should not be applied too tightly and should lift the cow slowly to allow time for the circulation of the limbs to become reestablished. The device is lifted until the hindfeet just touch the ground. Often, the cow will hang with the limbs slightly flexed. This should not be confused with unilateral flexion, which indicates peroneal paralysis. Next, one assistant on each side of the cow presses a shoulder into the paralumbar fossa while facing the hindlimb. The device is slowly lowered as the assistants attempt to force each hindlimb into a weightbearing posture and to reduce the flexion by manipulating the stifle and hock. As soon as any weight is supported by the two limbs, the device should be lowered 1–2 in. This process may have to be repeated several times.
Even if the cow does not stand, the lifted position provides an opportunity to manipulate the limbs, auscultate for crepitation, and perform vaginal and rectal examinations.
The chances of resolution are considerably enhanced by moving the cow to a location with an earthen floor. In warm, relatively dry weather, the best location for a recumbent cow is grassy pasture, although this means that a method to lift the cow must be readily available. Otherwise, the location selected should have a roof and some protection from the elements. These conditions often exist in a hay barn or implement shed, which may have the added benefit of allowing installation of a pulley system to lift the cow.
Moving the cow requires rolling her into lateral recumbency. The cow can then be slid over dry straw for a short distance by pulling on a rope attached to a lower forelimb and a halter rope. Transportation over longer distances can be accomplished using a suitably prepared farm gate hauled by tractor. The longest dimension of the farm gate is closely applied to the back of the cow still in lateral recumbency. A tarpaulin is placed on the gate to protect the cow from contact with the ground. Dry straw is spread on the tarpaulin, and the cow is rolled over onto the makeshift stretcher. The halter should be tied to the gate to minimize struggling, and a sack placed over the eyes to minimize alarm while the cow is being moved. The tail is best tied to the hock of the upper limb. Once moved, the cow should be restored to sternal recumbency. A few cows, particularly if <12 hr postpartum, will rise immediately after being moved to a location with good footing.
Recumbent cattle should be examined daily to determine any change in ability to rise or bear weight. The chance of improvement is very low if the cow does not show any improvement within 5 days of moving to a location with good footing and correction of any serum electrolyte abnormalities.
It is vital that recumbent cows be provided with clean water at all times. A shallow rubber feed bowl prevents spillage. If the cow does not drink, she must be given fluid therapy either by drench or parenterally. Every effort must be made to roll the cow from one side onto the other at least three times a day, with more frequent movement being desired. If this is not done, the weight of the cow results in continued ischemia of the muscles of the hindlimb and exacerbation of compartment syndrome.
Protection from the elements is essential. Rain and wind can reduce body temperature considerably and worsen shock if present. A windbreak of straw bales is vital. Straw bedding should be provided to help insulate the cow from the ground. A recumbent cow does not require a warm environment; however, in a cold environment, an inactive animal can gradually succumb to hypothermia.
The downer cows most difficult to treat are those that do not try to eat. A cow that salivates on its feed will not eat it later. Rather than being offered large amounts of feed, the cow should be tempted with sweet hay. This should be cleared away every 30 min if not accepted. Placing bitter-tasting weeds such as ivy or dandelion in the mouth may provoke salivation and an interest in eating. Lettuce and cabbage leaves are accepted by some cows. In extreme cases, the cow can be drenched with rumen contents.
Effective strategies to prevent milk fever are important to decrease downer cow syndrome. All dairy cows should be monitored closely around calving for early signs of parturient paresis (see Parturient Paresis in Cows). Prophylactic administration of calcium to all cows, beginning with cows entering their second or later lactation, is beneficial in herds with a high incidence of milk fever, especially in smaller farms that cannot implement feeding acidogenic salt diets.
The critical issue seems to be the length of time (several hours) from when clinical signs of milk fever begin until treatment. Every cow that has been successfully treated for hypocalcemia should, if necessary, be moved to a location with a good footing and remain there for 48 hr. Straw over sand provides good insulation and good footing.
Although a cow may rise after being recumbent for >14 days, this does not imply that a cow should be unmonitored for this period. So long as the cow looks bright, occasionally struggles to rise, and continues to eat and drink, recovery is a possibility. However, if the cow becomes listless, shows no interest in feed, or has decubital lesions or starts to lose condition, euthanasia on humane grounds must be considered irrespective of how long she has been recumbent. A cow that has decubital lesions, a poor appetite, or shows signs of wasting is unsuitable for salvage slaughter. Attempting to send animals in this condition to the slaughterhouse is considered an act of cruelty in many countries.
“Dragging” recumbent cows is illegal in some countries. Both veterinarians and producers must be aware of the legal interpretation of the word "dragging." Access to some locations may be so restricted that rolling the animal onto an improvised sled may be impossible. At all times, even when using a sled, great care must be taken to avoid injury to dependent parts of the animal such as the udder, ears, and tail.