Effect of feed intake level on the determination of apparent and standardized total tract digestibility of phosphorus for growing pigs

Abstract

The present study was conducted to investigate the effect of feed intake (FI) level on the determination of apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of phosphorus (P) for growing pigs fed diets containing moderate and low P concentrations. Seventy-two barrows (initial body weight (BW) = 41.2 ± 0.8 kg) were used in a randomized complete block design with a 3 × 3 factorial arrangement of 3 diets (a P-free diet, a cornstarch based low-P diet or a corn-soybean meal based moderate-P diet) and 3 graded FI levels (3, 4 or 5% of BW per day) with 8 replicate pigs per treatment group. The total collection method was used to calculate ATTD of P with a 5-d adjustment period followed by a 7-d collection period. The STTD of P was calculated by correcting ATTD of P for basal endogenous P losses (EPL) determined from feeding a P-free diet. Data were analyzed by the MIXED procedure of SAS. Linear and quadratic effects of FI level within each diet were determined by orthogonal polynomial contrasts. The results showed that daily basal EPL of pigs increased linearly with increasing FI level (P < 0.05). Pigs fed a low-P diet had lower dietary P intake, fecal P output, digested P, ATTD and STTD of P than that in pigs fed a moderate-P diet (P < 0.01). Dietary P intake, fecal P output, and digested P increased with increasing FI level within each diet (linear, P < 0.01). The ATTD (P < 0.01) and STTD (P < 0.1) of P decreased with increasing FI level. There were linear decreases in ATTD and STTD of P for pigs fed the moderate-P diet as the level of FI increased (P < 0.05). However, no linear or quadratic effect of FI level on ATTD and STTD of P was found in pigs fed a low-P diet. In conclusion, the ATTD and STTD of P decrease with increasing FI level for growing pigs. However, dietary concentration of P affects the ATTD and STTD of P responses of pigs to FI level.