Genetic, age, and diet effects on phytate degradation of laying hens studied in combined in vivo and in vitro assays

Endogenous mucosal phosphatases of chicken degrade phytate from the feed to a variable extent. The objective of this study was to investigate endogenous mucosal phosphatases as affected by laying hen strain, hen age, and dietary phosphorus (P) renunciation. Two cohorts of the strains Lohmann Brown-classic (LB) and Lohmann LSL-classic (LSL) were fed for 3 weeks, starting in week 27 and 39 of age, respectively, one of two diets with (P+) or without (P-) mineral P supplement. Total excreta were collected. In weeks 30 and 42, hens were sacrificed, and ileal digesta and duodenum mucosa were collected. Mucosa was freeze-dried before being used in a three-step <i>in vitro</i> assay. The concentrations of InsP isomers, <i>myo</i>-inositol (MI), P, and calcium (Ca) were measured in the excreta and digesta. InsP isomers were measured in the <i>in vitro</i> incubation residues. Most of the excreta InsP concentrations were lower in LB than in LSL (<i>P</i> ≤ 0.010), higher at 30 than 42 weeks (<i>P</i> < 0.001), and higher when fed P+ than P- (<i>P</i> < 0.001). In the ileum, the InsP₆ concentration was lower in LB fed P+ and in LSL fed P- than in other treatments (<i>P</i> = 0.027), while InsP₅ isomer concentrations varied with age × strain interaction and age (<i>P</i> ≤ 0.021). The MI concentration was higher in LB hens fed P- than LSL hens and hens fed P+ (<i>P</i> ≤ 0.005). After <i>in vitro</i> incubation, the InsP₆ concentration was higher with mucosa of 30-week-old hens fed P+ than in other treatments (<i>P</i> = 0.016). The InsP₆ concentration after <i>in vitro</i> incubation was highly heritable only in LB ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow><mml:msup><mml:mi>h</mml:mi> <mml:mn>2</mml:mn></mml:msup> </mml:mrow> </mml:math> = 0.62, <i>P</i> = 0.003) and a polygenic structure for this trait was detected. The consistent results from excreta, ileum digesta, and <i>in vitro</i> measures provide an extended view of endogenous mucosal phytate degradation primarily driven by a 6-phytase. Dietary P renunciation and aging of hens appeared to increase phytate degradation, possibly by increased expression of endogenous mucosal phosphatases. The differences between the two laying hen strains reveal different endogenous mechanisms and were reflected at the quantitative genetic level for the <i>in vitro</i> traits.