The small intestinal responses in the determination of true digestibility and the endogenous outputs of phosphorus in corn for growing pig using the regression analysis technique

Abstract It is of important methodological considerations to understand how the small intestine would respond to feeding of a series of assay diets deficient in gradient levels of phosphorus (Pi) associated with corn in growing pigs by the regression analysis technique (TRAT). A total of 48 barrows, with an average initial BW 32 kg, were randomly assigned to 6 grower pig diets and were fed close to ad libitum for 10 d, with 8-d adaptation and 2-d collection fecal samples, according to a randomized complete block design. Six cornstarch-based diets, containing 6 levels of Pi at 1.3, 1.9, 2.0, 3.6, 3.4 and 4.0 g/kg DMI, were formulated from corn. The gut permeability marker of D-mannitol was fed 0.30 g/kg BW at 4 h, prior to be sacrificed for sampling. ADG and the apparent ileal DM digestibility were linearly affected (P < 0.05); however, the ADFI, feed conversion ratio, the apparent fecal DM digestibility, transcellular gut permeability and the jejunal alkaline phosphatase kinetics were not affected (P > 0.05) by the increasing dietary levels of corn inclusion. There were linear relationships (P < 0.05), expressed as g/kg DMI, between the apparent ileal and fecal digestible Pi and the total intake of dietary Pi, suggesting that true ileal and fecal Pi digestibility (33.3±4.7 vs. 52.7±3.8%); and the endogenous Pi outputs (0.37±0.12 vs. 0.60±0.09, g/kg DMI) associated with corn could be estimated by the TRAT. Our results have shown that the intestinal physiological functions were not affected in the grower pigs fed on a series of test diets that were deficient in gradient levels of multiple assay nutrients, including macro-minerals, crude protein and amino acids supplied from the testing corn, for a period of 10 d, in the determination of corn-specific true digestibility and the endogenous outputs of Pi by the TRAT.