Effects of dietary potassium supplementation for growing turkeys on leg weakness, plasma potassium concentration, and selected blood variables.
The objectives of this research were to observe the effects of increased K in the diets of growing tom turkeys from 6 to 18 wk of age on body weight, feed-to-gain ratio, and leg weakness; to study the effects of time and temperature of blood storage after sampling and before centrifugation on plasma K concentration; and to evaluate plasma creatine kinase activity as an indicator of leg weakness. Male Nicholas White turkeys were fed corn-soybean meal based starter and grower diets from 1 d to 6 wk of age. At this time, each of three dietary treatments was assigned randomly to three pens of toms, 30 toms per pen. The dietary treatments consisted of 1) corn-soybean meal control (control) diets, 2) corn-soybean meal diets supplemented with 25% more K than the control diets contained (Mod K), and 3) corn-soybean meal diets supplemented with 50% more K than the control diets (High K). Potassium carbonate was used as the source of supplemental K for the Mod K and High K diets. Calculated K concentrations of the control diets fed from 6 to 9, 9 to 12, 12 to 15, and 15 to 18 wk were 0.84, 0.74, 0.57, and 0.54%, respectively. Results of laboratory analysis of the diets agreed closely with the calculated values. By 12 wk, toms fed the High K diets weighed less (P = 0.018) than toms fed the control diets, and this difference was still evident at 18 wk (P = 0.013), even though the High K groups were changed to the control diets at 12 wk. Toms fed the Mod K diets also tended to weigh less at 16 and 18 wk than those fed the control diets, however, the diet effect at the latter time was not significant (P > 0.05). There were no consistent effects of dietary K on feed efficiency. Total incidence of leg weakness at 12 wk was greater (P = 0.015) among toms fed Mod K and High K diets than for those toms fed the control diets. These results show that dietary K concentrations greater than those usually present in corn-soybean meal based diets for growing turkeys should be avoided. Increases in dietary K concentrations were associated with increases in plasma K concentration. Storage of blood after sampling and before centrifugation decreases the plasma concentration of K. The decrease is minimized when ambient temperature of storage is decreased. Accordingly, blood should be centrifuged immediately after sampling for accurate measurement of plasma K concentration. Plasma creatine kinase activity is not a good indicator of associated leg weakness unless physical activity and stress can be controlled before blood sampling.