Effects of dietary calcium and available phosphorus concentration on digesta pH and on the availability of calcium, iron, magnesium and zinc from the intestinal contents of meat chickens

Abstract

1. The effects of high calcium intakes on the pH and availability of calcium, iron, magnesium and zinc in the gastrointestinal tract (GIT) contents of meat chickens were studied in two experiments. 2. A high dietary concentration of calcium (25.3 vs 10.7 g/kg) increased the pH of crop and ileum contents, but did not influence the pH of the contents of other segments of the GIT. 3. The solubilities of minerals in GIT contents were reduced and the size of dissolved mineral complexes were increased as the digesta moved from the duodenum and jejunum to the ileum. 4. After feeding diets with calcium and available phosphorus concentrations (15.3 and 4.3 g vs 21.8 and 4.3 g vs 22.6 and 8.3 g/kg), centrifugation of GIT contents showed that most (70-92%) of the calcium, iron, magnesium and zinc was in an insoluble form. High calcium diets reduced the proportion of soluble zinc associated with small complexes, and high calcium and available phosphorus diets reduced the proportions of soluble magnesium and zinc associated with small complexes. 5. These findings explain the mechanism of the reduced availability of zinc and magnesium in high calcium and high available phosphorus diets.

Níveis de cálcio em rações de frangos de corte na fase inicial suplementadas com fitase

“…A depressão da atividade fitásica reduz a disponibilidade dos minerais, o que leva à redução da absorção do fósforo e outros minerais complexados com o fitato, que são nutricionalmente importantes (Shafey et al, 1991). A redução da atividade da fitase, em função da elevação do nível de cálcio da ração, também foi comprovada em experimento de Qian et al (1997).…”

“…A elevação da proporção de cálcio/ fósforo reduz significativamente o desempenho de frangos em rações à base de milho e farelo de soja, suplementadas com fitase (Leeson, 1999), provavelmente devido à reação do cálcio com o ácido fítico, formando o fitato de cálcio, que precipita e não pode ser hidrolisado pela fitase. Ao centrifugar o conteúdo intestinal de frangos de corte que consumiram rações com alto nível de cálcio (acima de 1,53%), Shafey et al (1991) verificaram que 70 a 92% do cálcio, ferro, magnésio e zinco estavam na forma insolúvel e sugerem que a elevação do pH intestinal, em função da elevação do nível de cálcio, reduz a fração solúvel de minerais e a sua disponibilidade para absorção. Para maior solubilização do fitato, é necessário manter os níveis de fósforo e cálcio inorgânicos nos limites mínimos necessários (Mitchell & Edwards Jr., 1996a), indicando que os níveis destes minerais devem ser reduzidos, quando a fitase for empregada durante a formulação (Ballam et al, 1984).…”

The effect of non-phytate phosphorus and phytase levels on performance, egg and tibia quality, and pH of the digestive tract in hens fed higher-calcium-content diet

“…The low level of P without F addition was found to have a negative effect on the pH in the small intestine, which increased to 6.21. Shafey et al (1991) similarly showed that the pH in the small intestine of broilers ranges from 5.5 to 6.6. However, because the pH was within this range, the dietary Ca complexes with the phytate made the phytate unavailable for F activity (Wilkinson et al, 2011).…”

Zinc availability and digestive zinc solubility in piglets and broilers fed diets varying in their phytate contents, phytase activity and supplemented zinc source

“…Second, the methodology implemented did not differentiate soluble Zn according to the size of the compounds to which it is associated, while Zn is more readily absorbed when associated with small compounds (Shafey et al, 1991). Third, the collected broiler intestinal contents may not be representative enough of digesta located close to the Zn absorption sites, probably located at the upper part of the small intestine.…”