Hypokalemia occurs commonly in inappetant adult cattle, particularly in lactating dairy cows because of the additional loss of potassium in the milk.
Hypokalemia is common in adult cattle with prolonged inappetence (>2 days), or in those receiving more than one injection of corticosteroids that have mineralocorticoid activity, eg, isoflupredone acetate. This is because mineralocorticoid activity enhances renal and GI losses of potassium. Hypokalemia is extremely rare in adult ruminants with adequate dry matter intake.
Animals with hypokalemia have generalized muscle weakness, depression, and muscle fasciculations. Severely affected animals are unable to stand or lift their head from the ground.
Serum biochemical analysis is required to confirm a suspected diagnosis of hypokalemia. A serum potassium concentration <2.5 mEq/L reflects severe hypokalemia; most animals will be weak, and some will be recumbent. A serum potassium concentration of 2.5–3.5 mEq/L reflects moderate hypokalemia, and some cattle will be recumbent or appear weak with depressed GI motility. In addition to measurement of serum potassium concentration, measurement of serum concentrations of sodium, chloride, calcium, and phosphorus, and serum activities of CK and AST can be very helpful in guiding treatment. Aciduria may be present in response to a marked decrease in urine potassium concentration.
Oral potassium administration is the treatment of choice for hypokalemia. Inappetant lactating dairy cattle should be treated with 60–120 g of feed grade KCl twice at a 12-hr interval, with the KCl placed in gelatin boluses or administered by ororuminal intubation. Adult cattle with severe hypokalemia (<2.5 mEq/L) should initially be treated with 120 g of KCl PO, followed by a second 120-g dose of KCl 12 hr later, for a total 24-hr treatment of 240 g KCl. Higher oral doses are not recommended, because they can lead to diarrhea, excessive salivation, muscular tremors of the legs, and excitability.
Potassium is rarely administered IV; the IV route is used only for initial treatment of recumbent ruminants with severe hypokalemia and rumen atony, because it is much more dangerous and expensive than oral treatment. The most aggressive IV treatment protocol is an isotonic solution of KCl (1.15%), which should be administered at <3.2 mL/kg/hr, equivalent to a maximal delivery rate of K+ at 0.5 mEq/kg/hr. Higher rates of potassium administration run the risk of inducing hemodynamically important arrhythmias, including premature ventricular complexes that can lead to ventricular fibrillation and death.