Sodium requirements, balance and tissue composition of growing pigs

The sodium requirements, balance, excretion, patterns and composition of some pig tissues were studied in two feeding trials and a balance trial followed by an additional feeding period with terminal tissue composition analysis. The growth of pigs fed a corn-soybean meal diet without added salt was severely restricted. Results confirm that a sodium requirement of .09% of the diet is adequate and that .20% NaCl supplementation is adequate for any natural diet for swine. Diets containing .065% sodium caused about a 25% reduction in growth when fed to 10-kg pigs but no significant reduction when fed to 27-kg pigs. Dietary retention was 96% for pigs fed .032% or .067% sodium. Retention was less per unit gain (gain was greater per unit sodium retention) fo9r pigs fed .032% sodium than for pigs fed .067% or more sodium. Those fed .032% sodium had a greater PCV after 1 week on trial and a smaller plasma sodium concentration after 2 weeks. The terminal tissue analyses showed that the pigs fed the lowest sodium diet had lower concentrations of sodium in plasma, muscle and bone, lower concentrations of chloride in plasma and muscle and a greater plasma potassium concentration. Crystal sodium of bone was not significantly affected.