The postileal digestion of phosphorus (P) may depend on both, the development of the gastrointestinal tract and microbial fermentation. Therefore, the influence of body weight (BW) and diet composition should be taken into account. The objectives of this study were to determine effects of dietary total P concentration on postileal P digestion in growing pigs, and to compare it between 25.9-kg growing, 61.3-kg growing-finishing, and 98.3-kg finishing pigs. Two experiments were conducted. In Exp. 1, 48 growing pigs (27.8 ± 1.7 kg BW) were surgically fitted with a T-cannula at the distal ileum and allotted to 6 dietary treatments. Corn-soybean meal (SBM) diet without dicalcium phosphate (DCP) supplementation was the basal diet with total P concentration calculated to be 3.3 g/kg. Five additional diets were formulated by the inclusion of DCP with 5.4 g/kg increments to the basal diet. Therefore, the calculated total P in the experimental diets were 4.3, 5.3, 6.3, 7.3, and 8.3 g/kg total P, respectively. In Exp. 2, 16 growing pigs (25.9 ± 1.3 kg BW), 16 growing-finishing pigs (61.3 ± 2.5 kg BW), and 16 finishing pigs (98.3 ± 3.9 kg BW) 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 with 14.5 g/kg of DCP). For both studies, 9 d experimental periods were used including 5 d of adaption, 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 linearly with increasing dietary total P level. In Exp. 2, ileal P output and digested P, and ATTD of P were affected by BW × Diet interaction. Compared to growing pigs, the growing-finishing and finishing pigs had greater amount of postileal digested P, proportion of postileal digested P to total tract digested P, apparent postileal digestibility of P, and hindgut disappearance of P. 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.
In conclusion, postileal P digestion was affected by BW with greater importance above 60kg, however, dietary total P level had marginal effects on postileal P digestion in growing pigs. Therefore, the BW effect and the role of large intestine on total tract P digestion should be considered.
Liu, J. B., Xue, P. C., Cao, S. C., Liu, J., Chen, L., and Zhang, H. F. (2018). Effects of dietary phosphorus concentration and body weight on postileal phosphorus digestion in pigs. Animal Feed Science and Technology. 242: 86-94. https://doi.org/10.1016/j.anifeedsci.2018.06.003