The relative availability of phosphorus in inorganic feed phosphates for young turkeys and pigs

Abstract

The relative biological availability of phosphorus in four inorganic feed phosphates was estimated in three experiments. Experiment 1, which involved turkey poults, compared monocalcium phosphate (MCP), hydrated dicalcium phosphate (DCP-hydr.) and anhydrous dicalcium phosphate, brand A (DCP-anhydr. A). The feed phosphates were added to a low-phosphorus basal diet at four levels: 1.0, 1.5, 2.0 and 2.5 g P per kg feed. Response parameters were live-weight gain, feed:gain ratio, P content of the tibia and the apparent digestion coefficient of P at the terminal ileum. Response to P-dose was lowest for all parameters with DCP-anhydr. as the P source. With MCP as the phosphorus source, apparent P-digestion at the terminal ileum responded significantly better to P-dose than with DCP-hydr. A linear response was obtained only with the lower three levels of DCP-hydr. and DCP-anhydr. and with P-content of the tibia as the response parameter. From the dose response curves, biological availability of P in DCP-anhydr. A, relative to that in DCP-hydr., was estimated by the slope ratio technique to be 0.71 (95% confidence limits of ratio: 0.58–0.91). In experiments 2 and 3, which involved young pigs aged 10–15 weeks, apparent digestion of P was used as the response parameter for estimating the relative biological availability of MCP, DCP-hydr. and DCP-anhydr. (brands A and B). DCP-hydr. and DCP-anhydr. were added to a low phosphorus basal diet at three levels: 0, 0.8 and 1.6 g P per kg feed and MCP 0 and 1.6 g P per kg feed. If biological availability of P in DCP-hydr. is set at 1.00, the values for DCP-anhydr. (brand A) and DCP-anhydr. (brand B) would be 0.887 (95% confidence limits: 0.769–0.998) and 0.879 (0.727–1.03). For MCP, biological availability of P was 1.25 and 1.16 in experiments 2 and 3, respectively. These values were significantly different from 1.00 ( P < 0.05).