Effects of dietary phosphorus concentration and body weight on postileal phosphorus digestion in pigs

Two experiments were conducted to determine the effects of dietary P concentration and BW on postileal digestion of P in pigs. In Exp.1, 48 growing pigs (BW: 27.8 +/- 1.7 kg) were fitted with a T-cannula at the distal ileum and allotted to 6 dietary treatment groups. The basal diet was a corn-soybean meal (SBM) based diet without dicalcium phosphate (DCP) supplementation, and dietary total P concentration was calculated to be 3.3 g/kg. Five additional diets were formulated by the inclusion of DCP in increments of 5.4 g/kg to the basal diet and thereby creating experimental diets that were calculate to contain 4.3, 5.3, 6.3, 7.3, and 8.3 g/kg total P, respectively. In Exp. 2, 16 growing pigs (BW: 25.9 +/- 1.3 kg), 16 growing-finishing pigs (BW: 61.3 +/- 2.5 kg), and 16 finishing pigs (BW: 98.3 +/- 3.9 kg) were surgically fitted with a T-cannula at the distal ileum. Each BW group of pigs was fed the moderate P diet (a corn-SBM diet without DCP addition) or the adequate P diet (a corn-SBM diet supplemented with 14.5 g/kg of DCP). In each study, the 9 d experimental periods consisted of 5 d of adaption period, 2 d of feces collection, and 2 d of ileal digesta collection. In Exp. 1, ileal and fecal P output, ileal digested P, total tract digested P, the apparent ileal digestibility (AID) and apparent total tract digestibility (ATTD) of P increased with increasing dietary total P level (linear, P < 0.01). There was no difference between the AID and ATTD of P for pigs within each diet. In Exp. 2, ileal P output and digested P, and ATTD of P were affected by the interaction between BW and diet (P < 0.05). Growing-finishing pigs and finishing pigs had greater amount of postileal digested P, the proportion of postileal digested P to total tract digested P, the apparent postileal digestibility of P, and hindgut disappearance of P than growing pigs (P < 0.05). The values for ATTD of P were greater than the estimates of AID of P for growing-finishing pigs and finishing pigs, regardless of diet (P < 0.05). In contrast, there was no difference between the AID and ATTD of P for growing pigs. In summary, postileal P digestion of pigs was affected by BW, but dietary total P level has marginal effects on postileal P digestion in growing pigs.