A note on sampling digesta from the ileum of broilers in phosphorus digestibility studies

The responses of broilers to increments of dietary P concentration in P retention and P prececal digestibility were studied in 2 experiments using Ross 308 broilers in their fourth week of age. The low-P basal diet was mainly based on corn, potato protein, and corn starch. Titanium dioxide was used as the indigestible marker. Monobasic calcium phosphate was added in 6 (experiment 1) or 5 (experiment 2) graded levels up to a maximum of 8.1 g of P/kg of the diet. Five (experiment 1) and 6 (experiment 2) replicated pens of 10 birds were used. Excreta were collected from trays underneath the pens. Birds were asphyxiated by carbon dioxide exposure and the ileum (from Meckel's diverticulum to 2-cm anterior to the ileo-ceca-colonic junction) was dissected. Digesta was collected from the entire section (experiment 1) or from 3 subsections of equal lengths (experiment 2). Excretion of P increased linearly with increasing dietary P concentration up to a level of about 5.2 g of P/kg of the diet and increased nonlinearly with further increase in dietary P. In contrast, P flow in the ileum increased linearly over the entire range of P intake. Up to the level of 5.2 g of P/kg of the diet, P excretion was slightly lower than P flow in the ileum, but responses in P excretion and P flow in the ileum were similar, suggesting that P excretion with urine is very low and unaffected by P intake when the birds are supplied with P below their requirement. Between the 3 subsections of the ileum, calculated digestibility was significantly different for the basal diet and the diet with the 3 lowest levels of P supplementation. We concluded that the response in P prececal digestibility to increments in dietary P concentration is linear over a wider range of dietary P than the response in P retention. When digesta is collected from the ileum for determination of P prececal digestibility, the first third of the ileum should not be considered.