The effects of salt and protein level on the performance and fecal consistency of piglets between 4 and 9 weeks of age

Recent research has shown that salt levels of minimal 3.5 g/kg diet result in best performance in piglets between 7 and 11 kg. In the US, pig diets tend to have higher salt levels and higher crude protein (CP) levels than in Europe. Higher CP levels may lead to higher protein breakdown, while higher salt levels may lead to increased water consumption, which might facilitate nitrogen clearance through the kidneys. Therefore, we hypothesized that high salt levels are more important when the pigs receive a high CP diet. For this experiment, 96 pens of 5 piglets were divided over 8 treatments in a 2 × 4 factorial design with 2 protein levels (189 vs 223 g/kg) and 4 salt levels (1.9, 2.5, 3.1, and 3.8 g/kg in the low protein diet and 1.9, 2.6, 3.2, and 3.9 g/kg in the high protein diet). Different salt levels were obtained by exchanging SiO2 for NaCl. The low protein diet was formulated to contain 11.8 g SID lysine and 9.85 MJ net energy/kg diet, while the high protein diet had 12.5 g SID lysine and 10.40 MJ net energy/kg diet. Salt level did not affect performance nor did it interact with crude protein level. Fecal consistency worsened as salt levels increased during the first week after weaning. The latter might be a result of either increased water consumption or increased osmotic pressure in combination with the piglets’ limited absorption capacity shortly after weaning, especially when receiving diets without zinc oxide or antibiotics. The higher nutrient density in the high protein diet resulted in lower feed intake with similar growth, leading to improved feed efficiency per kg diet, but not per MJ of net energy consumed. Based on the present experiment, we could not confirm our hypothesis that increased protein levels lead to higher sodium requirements in weaned piglets.