Effect of dietary phosphorus on selenium retention in postweaning swine

Two experiments were conducted to evaluate the effect of dietary Se and P levels on Se retention in postweaning swine. A 20% protein corn-soybean meal diet at two dietary Se levels (.3 and 5.0 ppm) and four total P levels (.50, .70, .90, 1.10%) were fed. Supplemental Se was provided from sodium selenite with inorganic P from dicalcium phosphate. In Exp. I, 151 pigs weaned at 4 wk of age were allotted by sex, litter and weight and fed their treatment diets for 28 d after a 7-d adjustment to a basal diet. Dietary Se level had no effect on performance measurements. As dietary P level increased, there was an increase in daily gain, feed intake and a decrease in feed to gain ratio. Dietary P resulted in similar plasma, longissimus muscle and kidney tissue Se values within each dietary Se level, while liver Se declined as dietary P level increased. Dietary P level had no effect on plasma, heart or liver glutathione peroxidase (GSH-Px) activity. In Exp. II, 32 barrows, after being fed their diets for a 28-d period, were placed in individual metabolism crates where a balance trial was conducted. Dietary P level reduced absolute and percentage Se retention, particularly at dietary P levels of .90 and 1.10%. Phosphorus retention was not affected by dietary Se. Neither dietary P nor Se level had any effect on N retention. These results suggest an effect of dietary P level on Se retention and liver Se, particularly at dietary P levels above the pig's P requirement, while the effect is minimal at or below the pig's P requirement.