Effect of Potassium and Hypomagnesemia on Insulin in the Bovine

Grass tetany in cattle has been associated with the consumption of early spring forages high in potassium (K) and low in magnesium (Mg). Alterations in serum Mg and K may affect intermediary carbohydrate metabolism, resulting in hypoglycemia and ketosis that often accompany grass tetany. We investigated these interrelationships by infusing potassium chloride (KCl) intravenously in normal (plasma Mg > 2.1 mg/100 ml) and Mg-deficient (plasma Mg < .7 mg/100 ml) 9-month-old Holstein bull calves and intraruminally into nonpregnant, nonlactating Holstein cows. Plasma levels of both K and immunoreactive insulin (IRI) were elevated (P<.01) by 1.14, 2, and 3% KCl (51, 64, and 135 mg K/kg) in calves and by 550 g KCl (440 mg K/kg body weight) in cows. Plasma K was lower (P<.01) and IRI higher (P<.01) in Mg-deficient calves than in normal calves during 2% KCl infusion. Elevated plasma K and IRI were accompanied by lower plasma glucose in normal calves (P<.05) and cows (P<.001). Elevated plasma glucose (P<.05) in Mg-deficient calves may have resulted from stimulation of glucagon secretion by abnormally high insulin levels. These results suggest that prolonged elevation of K and insulin in ruminants could lead to a series of metabolic disturbances that may play an important role in the etiology of grass tetany.