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Application of a kinetic model to describe phosphorus metabolism in pigs fed a diet with a microbial phytase

Dias, R.S., Lopez, S., Moreira, J.A., Schulin-Zeuthen, M., Vitti, D.M.S.S., Kebreab, E., France, J.
Journal of agricultural science 2010 v.148 no.3 pp. 277-286
nutrient resorption (physiology), swine feeding, isotope labeling, intestinal mucosa, bone mineralization, heart, phosphorus, stable isotopes, feed rations, blood chemistry, skeletal muscle, feces, temporal variation, simulation models, phytases, feed additives, nutrient retention, kidneys, swine, liver, mineral metabolism, food animals, dietary minerals
The objective of the current study was to apply the Vitti–Dias model to investigate phosphorus (P) metabolism in growing pigs fed a diet supplemented with microbial phytase. The basal diet contained maize, defatted rice bran, vegetable oil, soybean meal, limestone, salt and a vitamin and mineral mix. There was no inorganic P in the diet and phytase was added at levels of 253, 759, 1265 and 1748 phytase units (PU)/kg of feed. The compartmental model included four pools of P: (1) gut lumen, (2) plasma, (3) bone and (4) soft tissue. A single dose of 32P was administered, and specific radioactivity was measured in plasma, faeces, bone and soft tissue (muscle, heart, liver and kidney) at different times post-dosing for calculation of P flows between pools. Total P absorbed showed a negative relationship with total P excreted in faeces and was strongly correlated with bone P retention, suggesting that absorbed P was channelled to bone to address its physiological growth. Average efficiency of metabolic utilization of absorbed P was estimated to be 0·94, with 0·52 g/g of total net P balance being accreted in bone and the rest in soft tissue (including muscle and some vital organs). The Vitti–Dias model provided suitable representation of P interchange between compartments (in particular, flows between gut and plasma and partitioning of available P between bone and soft tissue), resulting in estimates of P flows comparable with values calculated from balance data.