Modeling of parameters affecting phytate phosphorus bioavailability in growing birds

University of Georgia, Department of Poultry Science, Athens, Georgia 30602, USA.

The current study was undertaken to establish a population from an unselected random-mating chicken population for the development of a model to predict factors that affect phytate P utilization in growing birds. A population was established from a mating of 40 male and 200 female chickens from the Athens Canadian randombred population. At 4 wk of age, birds were housed in individual metabolic cages and fed a diet containing 1.06% Ca, 0.35% total P, and 0.03% available P. After 3 d of acclimatization, feed consumption (FC) was measured and excreta produced in 3 consecutive d were collected. Individual 4-wk BW, BW gain (BWG), phytate P intake (PPI), inorganic P intake (IPI), Ca intake (CaI), N intake (NI), and energy intake (EI) during the 3 d excreta collection period were also measured. Feed conversion ratios (FCR) and relative growth rate were calculated. Phytate P bioavailability (PPB), Ca bioavailability (CaB), and N bioavailability (NB) were estimated from the disappearance of the nutrients during the passage of feed through the gastrointestinal tract. Energy bioavailability (EB) was measured by bomb calorimetry as the difference in the gross energy of the feed and the energy of the excreta. The major factors affecting PPB were CaB and EB for both sexes. In the males, BW contributed significantly to PPB. However, in the females, NB also contributed significantly to PPB. Faster growing birds tended to have a reduced retention time of feed compared with slow growing birds, and as a result utilized phytate P less. Birds that are able to utilize phytate P better are putatively able to release P for energy utilization. Therefore, the birds that were able to utilize phytate P better were also better energy utilizers.