Downer Cows (Alert Downers)

John A. Angelos • Bradford P. Smith •

John R. Middleton

■ Definition and Etiology Downer cows, down cows, or downers are cattle that are recumbent and cannot stand; those that can maintain sternal recumbency while continuing to eat and drink are classified as “alert downers.” Common underlying causes of recumbency in cattle include severe mastitis, metritis, musculoskeletal disease (primary musculo­skeletal injuries, including fractures and torn muscles/tendons), neuropathies secondary to pelvic trauma (calving paralysis), spinal cord compression (e.g., secondary to lymphosarcoma), and metabolic disease (hypocalcemia, hypokalemia, hypophos­phatemia, hypomagnesemia).¹ After the initial episode of recumbency, secondary muscle and nerve injury caused by extended periods of recumbency on a firm surface may further exacerbate the recumbency.

Identifying underlying causes of recumbency in downer cattle represents a diagnostic challenge for the practitioner. Assessing prognosis and determining reversibility of the underlying condition are necessary for practitioners to assist producers in making treatment decisions, as well as to conform to laws and abide by ethical norms surrounding humane handling of downer animals. In short, dragging of downer livestock is considered inhumane, and downer livestock that are in distress or that do not respond to treatment should be humanely euthanized.

■ Epidemiology and Pathogenesis It is reported that 3.8% to 28.2% of all cows with milk fever become alert downers,^2-5 and the mortality rate is 20 to 67%.^3-7 The incidence of the condition (24 hours or longer) was 21.4 cases per 1000 cow-years in Minnesota dairy herds, with a 33% recovery rate.⁷ Fifty-eight percent of downer cases occurred within a day of calving, and 97% occurred within the first 100 days after calving.⁷ Because the pressure damage done to muscles and nerves is aggravated by recumbency, it is desirable to have the animal on soft bedding (e.g., sand, grass) and to have the animal stand as soon as possible.

■ Clinical Pathology Laboratory testing for metabolic causes of recumbency would be ideal in all circumstances, but this is often not feasible or possible.

Of 16 normal cows anesthetized for 6 to 12 hours in sternal recumbency with the right hindlimb under the body, 8 were unable to stand on recovery and became alert downers.⁸ Those that could stand exhibited swelling and stiffness and peroneal nerve deficits and paresis in the right hindlimb.⁸ These signs typically appear in cows that have been recumbent for several hours on a hard surface. As pressure applied to a nerve increases, nerve conduction is impaired and eventually lost.⁹ Serum CK values in experimental downer cows increased, starting at 12 hours and continued to increase up to 48 hours, and then decreased, even though the cow remained down.⁸ The CK values at 12 and 24 hours did not differ statistically between the cows that could rise after anesthesia and the downers. After 48 hours and 96 hours, the downers had higher mean CK values than did the ambulatory cows, but the range in values was broad.⁸ The clinical difference between cows that recovered and those that remained downers was attributed to damage to the sciatic nerve or its branches, particularly the peroneal nerve.⁸ Peroneal nerve damage results in knuckling over at the fetlock. In another study of downers, AST levels were greatly elevated on days 4 to 7, even after CK levels fell.¹⁰

Serum levels of creatine phosphokinase, AST, and lactate dehydrogenase have been examined to determine whether these indices of muscle damage can help predict recovery of recumbent dairy cattle. Of the three enzymes, AST has been shown to be most useful in predicting nonrecovery. Dairy cattle with an AST level higher than 171 IU/L are 80% more likely not to recover than a dairy cow with an AST level lower than 171 IU/L.¹¹

CSF collected from recumbent adult dairy cattle with spinal cord lesions (neoplasia, trauma, or infectious process) had significantly higher total protein concentrations and total nucleated cell counts than did recumbent adult dairy cattle without spinal cord lesions, which suggests that CSF analysis may be useful in differentiating alert downer cows with spinal lesions from those without.¹² Cows with CSF protein levels lower than 0.25 g/L and total nucleated cell counts of 4.5 or lower were predicted to not have a spinal cord lesion, whereas cows with total nucleated cell counts higher than 4.5 or a protein concentration exceeding 0.39 g/L were predicted to have a spinal cord lesion, according to the statistical modeling performed in the study.¹²

■ Treatment Many downer cattle are treated empirically for suspected metabolic abnormalities and response to treatment aids in establishing the diagnosis.

Devices that aid and promote standing traditionally include hip lifters (hip clamps), slings, and inflatable bags. Although these devices help less severely affected animals stand temporar­ily, they do not allow the animal to stand comfortably for hours and may even cause further trauma in animals that struggle. For these reasons, the use of water flotation has been explored as a tool in the management of downer cows. Rasmus­sen¹³ first reported on the use of a warm-water flotation system in Denmark in 1982. Commercial flotation systems practical for cows (Aqua Cow Rise System [http://www.aquacowsystem.com] and Aqua-Cow-Rise System [http://kirbymfg.com/aquacow.htm]) are marketed in the United States.

For flotation therapy to allow the best chances for recovery, the animal should first be examined to determine that it is a good candidate for flotation, by ruling out fractures, severe spinal cord compression, and severe systemic illness. Identifying and correcting electrolyte disturbances (e.g., hypocalcemia, hypophosphatemia, hypomagnesemia, hypokalemia) are required for successful application of flotation therapy. Once metabolic or systemic illnesses have been addressed and the cow is considered strong enough to stand once supported by water, the cow is placed in the flotation tank as follows: (1) the water tank is positioned near the downer cow; (2) the wheels and tongue are detached, and both ends of the tank are removed; (3) a mat is pulled from the tub to a position beside the downer cow, and the animal is rolled or slid onto the mat; (4) the mat is winched or otherwise pulled into the tub, and the ends of the tub are put in place; they seal with rubber gaskets and large turnbuckles; and (5) the cow's head is held up a few inches by a rope halter, and a hose is inserted into the tub, which is filled with water as quickly as possible; the water temperature should be 37.7° C to 38.7° C (100° F to 102° F).

If no hot water is available near the cow, or if the tub is not next to dirt or grass suitable for the cow to exit on, the wheels can be put back on and the cow easily transported by trailer to a better location. In addition, it is helpful to have an assistant support the tail or have a means to pull the tail once the cow attempts to rise. This helps the cow maintain a sternal position during early efforts at struggling before the cow is actually standing. Before flotation of lactating cattle at the University of California, Davis, cows are milked, and teat ends are sealed with a rubber teat sealant; this is removed once the cow is removed from the tank before milking. The sealant is reapplied after milking in preparation for the next flotation.

Once the cow is standing in warm water, it is possible to determine which limb or limbs are paretic or painful by observ­ing which limbs the cow is using to support weight. Most cows calm down and relax in a standing position within 5 minutes. Most will eat hay, and even primiparous heifers that have not been handled much seem to be remarkably calmed by the warm water. Unlike horses, cattle do not panic or attempt to jump out. The cow can be left in the water for 12 to 24 hours. If the water temperature drops below 35° C (95° F), some water should be released from the discharge valve and replaced with hot water; this is especially recommended in cold weather. When the decision is made to remove the cow from the tub, the water is drained, and the end of the tub facing the dirt, sand, or grass is opened. The cow is encouraged to exit slowly into a pen with good footing. Some cows fall as the water is let out, and others collapse once they try to walk. By observing how a cow is ambulating on exit, it is possible to determine whether hobbles should be placed onto the cow before the next flotation.

Careful observation as the cow moves can be helpful in trying to locate anatomic or functional problems. The animal that collapses can be pulled out on the mat and left on suitable bedding, dirt, sand, or grass until refloated after a period of rest. Advanced planning on location is important for successful use of flotation therapy. Cows that can walk out into a pen may or may not be able to stand by the next day and may need to be refloated. Cows may need to be floated for up to 10 consecutive days before they can arise by themselves. If cases are carefully selected to rule out fractures, severe traumatic stifle injuries, septic arthritis, and spinal cord compression, a recuperative success rate of 46% to 90% can be expected.^13,14

Flotation is most effective if applied early, before a downer cow develops serious myopathy and neuropathy. Studies have shown that water flotation is practical and effective, even when cattle have been down for 24 hours or longer.¹ The sooner a postparturient alert downer cow can be floated after onset of recumbency, the sooner it can resume standing. In one study of postparturient alert downer cattle treated with flotation therapy, the mean time to resumption of standing was shorter for cattle floated within 1 day of going down (mean, 2.8 days to resumption of standing) than for cattle floated after being down for 2 days or longer (mean, 5.3 days to resumption of standing).¹⁴