Comparison of retention and prececal digestibility measurements in evaluating mineral phosphorus sources in broilers

The objectives of this study were to compare measurements of retention and prececal (pc) digestibility in evaluating mineral phosphorus (P) sources in 3- and 5-wk-old broilers. A corn-soybean meal-based basal diet was used (0.35% P on DM basis). Anhydrous monosodium phosphate (MSPa) or anhydrous dibasic calcium phosphate (DCPa) was supplemented to increment the P concentration by 0.08%, 0.16%, and 0.24%. Titanium dioxide was used as the indigestible marker. Two retention trials with excreta collection from d 16 to 20 and d 30 to 34 were conducted (n = 8 birds per diet). Another 8 pens of 10 birds from the same hatch were allocated to each diet on d 11 or 25 each to measure pc digestibility in both age periods. After 10 d of feeding, these birds were euthanized and the content of a defined section of the terminal ileum was obtained. Percentage P retention and pc digestibility for MSPa and DCPa were calculated by linear regression analysis. In 3-wk-old broilers, P retention for MSPa was 70% and significantly higher (P < 0.001) than for DCPa, (29%). Values determined for pc digestibility at the same age were very similar (67% for MSPa and 30% for DCPa; P < 0.001). In 5-wk-old broilers, P retention was 63% (MSPa) and 29% (DCPa; P < 0.001) and pc digestibility was 54% (MSPa) and 25% (DCPa; P = 0.002). We concluded that both retention and pc digestibility can be used for evaluating mineral P sources in broilers based on a regression approach. In 3-wk-old broilers, results obtained with both approaches were the same. In 5-wk-old broilers, the ranking of the 2 P sources was also the same for both approaches. Values did not differ significantly between the 2 age periods, but further studies on the relevance of broilers' age in P evaluation are suggested.