The role of dietary phytate (inositol hexaphosphate) in the regulation of intestinal mucosa phytase was investigated in chicks. Seven-day-old chicks were grouped by weight into six blocks of three cages with six birds per cage. Three purified diets [a chemically defined casein diet, a chemically defined casein diet plus sodium phytate (20 g/kg diet) and a chemically defined casein diet plus sodium phytate (20 g/kg diet) and microbial phytase (1000 units/kg diet)] were randomly assigned to cages within each block. Chicks were fed experimental diets from 8 to 22 days of age then killed, and duodenal mucosa and left tibia removed. Phytase activity in duodenal mucosa, growth performance and bone ash content were determined. Addition of phytate to the chemically defined casein diet reduced (p < 0.05) the Vmax of the duodenal brush border phytase, but the Km of the enzyme was not affected. Addition of phytate also reduced (p < 0.05) weight gain, feed intake, feed efficiency and percentage ash. Addition of microbial phytase fully restored the feed efficiency (p < 0.05), but Vmax and body weight gain were only partially restored (p < 0.05). In conclusion, it would seem that dietary phytates non-competitively inhibit intestinal mucosa phytase.

L’optimisation de l’utilisation de phosphore reste un enjeu majeur pour assurer la durabilité de nos filières avicoles et porcines. Aujourd’hui, l’utilisation de coproduits, relativement riches en fibres alimentaires, est grandissante. Or, les fibres alimentaires sont reconnues pour moduler les processus de digestion et la digestibilité des nutriments. Ce travail de thèse a permis de progresser sur les mécanismes digestifs engendrés par l’apport de coproduits riches en fibres alimentaires et leurs effets sur la digestion des minéraux, en lien avec la phytase microbienne, spécifiquement chez le porc et le poulet. Leurs conséquences métaboliques en terme de balance minérale et d’équilibre acidobasique ont également été mises en évidence Les connaissances acquises vont contribuer à l’amélioration de l’apport en minéraux, notamment de phosphore et de calcium, dans des formules diversifiées chez le porc et le poulet. A terme, ceci permettra de mieux adapter nos systèmes d’alimentations au regard des enjeux de durabilité. / The optimisation of the use of phosphorus remains a major challenge to ensure the sustainability of poultry and pig industry. Today, the use of co-product, relatively rich in dietary fibre, is increasing. However, dietary fibre is known to modulate digestion processes and digestibility of nutrients. This work contributed to progress on the digestive mechanisms generated by the intake of dietary fibre from coproducts and their effects on the digestion of minerals, in relation with microbial phytase, specifically in pigs and chickens. Their metabolic consequences in terms of mineral and acid-base balance have also been demonstrated. The knowledge gained will contribute to the improvement of the intake of minerals, in particular phosphorus and calcium, in diversified formulas in pigs and the chicken. Finally, this will allow us to better adapt our feeding systems to the challenges of sustainability.