Modeling the fate of dietary phosphorus in the digestive tract of growing pigs1

Abstract

Environmental effects of excess P from manure and the soaring price of phosphates are major issues in pig production. To optimize P utilization, it is crucial to improve our capacity to predict the amount of P absorbed, while taking into account the main factors of variation. Mathematical modeling can represent the complexity of the processes and interactions in determining the digestive utilization of P in growing pigs. This paper describes and evaluates a model developed to simulate the fate of the dietary forms of P in the digestive tract of growing pigs, with particular emphasis on the effect of dietary Ca and exogenous phytase on P digestive utilization. The model consists of 3 compartments associated with specific anatomical sections: stomach, proximal small intestine, and distal small intestine. The main metabolic processes occurring in these sections are, respectively, P solubilization/insolubilization and phytate P hydrolysis, and P absorption and P insolubilization. Model parameters governing these flows were derived from in vitro and in vivo literature data. The sensitivity analysis revealed that the model was stable within a large range of model parameter values (±1.5 SD). The model was able to predict the efficacy of Aspergillus niger microbial phytase in accordance with literature values, as well as the decreased efficacy of plant phytase compared with microbial phytase. The prediction capabilities of the model were assessed by comparing actual and simulated P and Ca apparent total-tract digestibility (ATTD) based on published pig data not used for model development. Prediction of P digestibility across 66 experiments and 281 observations was adequate [P ATTD observed = 0.24 (SE, 0.943) + 0.98 (SE, 0.0196) × P ATTD predicted; R(2), 0.90; disturbance error (ED), 96.5%], whereas prediction of Ca digestibility across 47 experiments and 193 observations was less accurate (Ca ATTD observed = 11.1 + 0.75 × Ca ATTD predicted; R(2), 0.78; ED, 20.4%). A lack of agreement between experimental and simulated Ca digestibility was found. This model is, therefore, useful in evaluating P digestibility for different feedstuffs and feeding strategies. It can also be used to provide insight for improving dietary P utilization, especially from plant sources, by quantifying the effect of the mean sources of variation affecting P utilization.

Modeling the metabolic fate of dietary phosphorus and calcium and the dynamics of body ash content in growing pigs

“…4a and 4b), as previously shown by Pointillart and Fontaine (1983) and Létourneau-Montminy et al (2011). This finding is in accordance with number of studies showing hyperphosphaturia during Ca imbalance (Vipperman et al, 1974;Létourneau-Montminy et al, 2011).…”

“…Dietary Ca and P are absorbed in the small intestine through a combination of active and passive flows (Fox et al, 1978) after complex digestion processes such as solubilization, insolublization, transition, and hydrolysis. The representation of Ca and P flows from the gastrointestinal tract to the extracellular fluids is a simplification of the model that described the fate of dietary Ca and P in the digestive tract of growing pigs (Létourneau-Montminy et al, 2011).…”

“…The ATTD of the dietary phytate P and nonphytate P from plant forms were previously estimated (Létourneau-Montminy et al, 2011, 2012. For nonphytate P from mineral and animal origin, the P ATTD reported in Sauvant et al 2004was used (Table 1).…”

“…The interaction between microbial and plant phytase was also taken into account given that they compete for the same substrate. The interaction between phytate and phytase were assumed to be negligible, as shown by Létourneau-Montminy et al (2011, 2012.…”

Methodological aspects of determining phosphorus digestibility in swine: A review

“…Non-phytate P of mineral, animal and plant origins remains highly digestible for pigs regardless of the non-phytate P concentration, as evidenced by their estimated digestibility coefficients. It is likely that phytate P cannot be totally hydrolyzed in gut due to the limited solubility of phytate P, which depends on pH condition and the transit time of digesta ( Létourneau-Montminy et al., 2011 ). Phytate P utilization depends on some modulating dietary factors.…”