Mild to moderate hypokalemia is a very common metabolic disturbance in cattle and is commonly encountered secondary to anorexia as well as a plethora of diseases. Fundamentally, any condition that causes a bovine patient to go off feed will likely result in mild hypokalemia, explains Simon Peek, BVSc, MRCVS, PhD, Dipl. ACVIM, University of Wisconsin-Madison.
Cattle do not have an endocrine mechanism by which they can control potassium levels in their blood stream (unlike calcium for example) within a narrow range and so are reliant on the balance between uptake from their diet and output in urine and feces. When the dietary intake is impaired levels will go down. Hence, dairy cattle in early lactation with common conditions such as LDA, metritis, mastitis or ketosis will probably have a measured blood potassium level that is a little below the normal reference range, adds Peek.
Hypokalemia can occur in both first lactation animals as well as multiparous cows, “Although some of the biggest herd problems that I have encountered have been in first-calf heifers, where the dairy is simultaneously experiencing a lot of ketosis problems in that group of animals commonly due to overconditioning of springers and/or husbandry errors that have led to markedly diminished dry matter intakes in very late pregnancy,” Peek says.
However, when a cow or heifer has experienced severe hypokalemia, Peek says that following recovery they do not appear to be at greater risk for developing the severe form again.
The clinical signs that are seen with mild hypokalemia will pertain to the primary condition not the hypokalemia itself. However, if severe hypokalemia occurs then the animal will start to show more specific signs related to the hypokalemia. Peek says these will begin with muscle fasciculations, often seen over the triceps and caudal thighs, and increasing difficulty rising from recumbency which may progress to profound weakness and a complete inability to get up or even support the weight of the head or body. "In fact, severely hypokalemic cattle often show such profound weakness/flaccidity that they resemble botulism cases," Peek notes.
A normal reference range for blood potassium in cattle is 3.6 – 5.4 mEq/L, with mild hypokalemia this will fall into the 2.5–3.5 mEq/L range but will need to drop to 2.2 or below before an animal will exhibit a sustained recumbency. “Most producers will observe that cattle with severe hypokalemia progress from being apparently able to stand to so weak that they cannot rise within 24 hours, so it is an acute condition to the naked eye, in reality the early signs are so non-specific that there is likely more chronicity to the development of the condition than is easily appreciated,” Peek says.
Diagnostics for hypokalemia
Blood work is the only way that one can diagnose hypokalemia in the live animal. “It’s important that the sample be taken and then analyzed promptly,” Peek advises. “Either serum or plasma can be used, but whichever sample is chosen it is important that the analysis be run, ideally, within two to three hours. If the red blood cells are allowed prolonged contact with the non-cellular serum/plasma component in a vacutainer tube then potassium leaks out of the cells into the serum/plasma and falsely elevates the measured value.” This, he says, will mislead the veterinarian as to the true potassium level in the blood. “We do not have a good or practical way to measure whole body potassium levels, so the blood numbers have to suffice,” he adds.
If an animal dies before blood can be obtained and severe hypokalemia is suspected, there is some merit to submitting muscle tissue from the carcass to a pathologist because there will be histologic changes in muscles of a severely hypokalemic patient. “However, muscle tissue should be obtained from non-weight bearing muscles such as the muscles between the ribs or diaphragm rather than larger limb muscles because the latter often have severe changes in down cows following recumbency for any reason,” Peek says.
Peek believes that awareness of hypokalemia as a pertinent condition in dairy cattle has led to the increased the amount of potassium supplementation given to sick cows in the fresh pen via oral drenches. “There is an association between ketosis and severe hypokalaemia, particularly in cattle under treatment for repeat, chronic ketosis and so it is relevant to implement potassium supplementation in oral fluids to all cattle in this category.”
The best intervention on-farm is oral supplementation by pumping potassium-containing fluids into the animal. With severe hypokalemia (measured blood level less than 2.2 mEq/L) Peek suggests 0.5 lb of potassium chloride every 12 hours for two treatments and then re-
measure the blood levels. “If you continue to administer that dose of potassium for more than two treatments, the cow will develop significant diarrhea and you may actually also ‘overshoot’ the normal blood range and that can have serious consequences on cardiac function,” Peek explains.
Peek says for cattle with potassium levels that are below the normal range, but not that severe, or that you are concerned about preventing hypokalemia without measuring the blood value, it is prudent to employ lower level supplementation such as 0.25 lb of potassium in oral fluids as part of the drench daily. Many commercial fresh cow type drenches contain potassium chloride at approximately this level. “In a hospital setting we usually utilize intravenous potassium containing fluids as well as oral fluids, but it is many people’s impression that the oral route is a more reliable means of bolstering potassium levels, and very few cattle in the field are put on IV drips,” notes Peek.
Because very few grade cattle will have blood work analyzed routinely, it is probably prudent to consider potassium supplementation as mandatory for a cow/heifer that you are treating for recurrent ketosis, and to include potassium in oral fluids anytime that you drench a fresh cow with one of the other common fresh cow disorders, says Peek. Prolonged anorexia would be another strong indication for potassium supplementation in oral fluids.
As with most conditions the earlier the treatment, the better the prognosis. But with severe hypokalemia that has progressed to recumbency, Peek says the prognosis deteriorates to probably less than 50%. “If aggressive supplementation with potassium is performed in a recumbent animal and that individual is still recumbent after 24–48 hours then the prognosis is grave with less than a 10% chance of ever standing again,” he says. “If intervention occurs before recumbency then the prognosis is much more favorable — the majority of these cattle will survive.”
Be cautious with other treatments
There are other treatments that are sometimes given to cattle with fresh cow problems that can worsen hypokalemia. “Probably the other major risk factor that we have been concerned with is the administration of therapeutic agents that cause the lowering of blood potassium levels and/or whole body potassium levels,” Peek says. “Via a variety of physiologic mechanisms many of the treatments used for ketosis actually serve to exacerbate hypokalemia whilst treating the ketosis. Obviously ketosis treatments have been used in dairy cattle for a very long time and yet this condition is relatively newly recognized so there must be other contributing factors.”
One should be careful about the use of steroids that increase potassium loss via urine for ketosis cases, particularly repeated use, warns Peek. One example is isofluprednone acetate. “However, I would be careful to point out that although we incriminated these types of steroids quite specifically in the development of severe hypokalemia when the condition was first recognized about 15 to 20 years ago, we currently still run into the condition in situations when these agents have not been used or where they have been used at conventional labeled doses,” he explains. “Any individual undergoing repeated treatment for ketosis should be specifically potassium supplemented.”
Potassium in forages can contribute to overall levels, but that’s not the area to focus on. Peek says currently potassium levels in forages are generally much higher than many years ago, possibly associated with greater manure spreading on forage fields. “It has not proven very helpful or useful to attempt to manipulate the potassium intake through finessing the TMR in problem herds. We always recommend a thorough ration evaluation when investigating a problem with severe hypokalemia but are often addressing those factors that contribute to other metabolic problems, (often ketosis) rather than tinkering with the finer detail of potassium levels in the ration.”
Peek adds that using an integrated management approach that reduces the likelihood of moderate to severe ketosis in early lactation, and by an awareness of the need for potassium supplementation in at-risk cattle, that hypokalemia can be prevented or reduced on the dairy.
A retrospective study (Peek, et al) looked at 17 lactating cattle from 15 different farms from 1991–1998. Of the 17, 13 were recumbent at presentation while the remaining four became recumbent within six hours of presentation. Recurrent ketosis was the most common antecedent medical condition in affected cattle in 15 of 17 cases.
Necropsy on 10 of the cattle demonstrated ischemic muscle damage subsequent to recumbency and varying degrees of hepatic lipidosis. Aggressive potassium supplementation was instituted in all 17 cases either orally, intravenously or by a combination of both routes. Of the seven surviving individuals, potassium supplementation was by both oral and intravenous routes in five, by the oral route in one and intravenously in one.
The study concluded that hypokalemia should be considered in the differential diagnosis of weakness and recumbency in the early lactational period, particularly in individuals with a history of recurrent clinical ketosis.
Other factors that could have contributed to development of severe hypokalemia in cattle in this study included prolonged anorexia, intracellular shifting of potassium due to insulin release — either as a primary therapeutic agent or secondary to repeated administration of glucose precursors — and enhanced urinary potassium excretion due to excessive use of exogenous corticosteroids with mineralocorticoid activity.