The effect of dietary P level and the Ca:available P on Na‐dependent phosphate transport in the small intestine of weanling pigs

Abstract

Feeding a low P diet to rodents, has been shown to increase Na-dependent phosphate transport in the small intestine. However, results reported in the literature are confounded by the feeding of wide Ca:available P (aP) in excess of 20:1. The objectives of this study were to determine the effects of a low P diet and the Ca:aP on Na-dependent nutrient transport. Intestines (jejunum) from weanling piglets fed an adequate or a low P diet with adequate or low Ca (Ca:aP ranged from 1.4 to 4.3) were mounted in modified Ussing chambers. Initial basal short circuit current, resistance, and potential difference did not differ (P>0.10) between treatment groups. As expected, Na-dependent phosphate transport was increased (P=0.015) from 7.00 to 13.04 μA/cm2in the jejunum as dietary aP level was decreased. Na-dependent glucose uptake increased (P=0.067) from 11.39 to 17.9 μA/cm2as dietary P level was decreased. However, no dietary Ca effects or P × Ca interactions were detected (P>0.10) for Na-dependent phosphate or glucose transport in the intestine. This data indicates that the level of aP in the diet is the main factor effecting Na-dependent phosphate uptake in the small intestine. Varying the Ca:aP in low P diets from 2.5 to 4.3, by adjusting Ca levels, had no effect on Na-dependent phosphate transport. Based on the results of this experiment, negative effects often observed when a wide Ca:aP is fed on P utilization are not due to alterations in Na-dependent phosphate uptake. Surprisingly, Na-dependent glucose uptake was increased 36% by feeding pigs a low P diet and was also independent of both Ca level and Ca:aP in the diet.