Effect of dietary calcium level on mineral and trace element utilization from a rapeseed (Brassica napusL.) diet fed to ileum-fistulated pigs

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Abstract
The bioavailability of intrinsic minerals in rapeseed (Brassica napusL.) meal was studied in growing, fistulated pigs. Furthermore, the effect on mineral availability of an extrinsic Ca supply to this diet, high in phytate, was observed. Comparisons between small intestinal and total gastrointestinal absorption were accomplished for minerals and other dietary components. N retention increased as the dietary Ca intake increased, but dropped, in general significantly, throughout the experimental period, indicating that factors other than protein were limiting for growth. The highest dietary Ca level increased the absorption and retention of Ca and Mg. In contrast, addition of CaCO3did not influence the apparent absorption and retention of P, Fe, Zn, Cu and Mn. The majority of observed blood variables was not affected by the Ca content of the diet. Zn status-related variables were, however, thoroughly depressed by duration of the experiment and it seems probable that the amount of absorbed Zn was a factor limiting growth. Total gastrointestinal balances showed a Zn retention of 4.7 mg/d, which accounted for 13.6 % of that ingested. This low absorption of Zn may have been due to the high intrinsic content of phytate. Apparent absorption of organic matter, ash, N and S was significantly greater calculated from faecal contents than from ileal contents, indicating a disappearance of material in the caecum–colon section of the gastrointestinal tract. The minerals which were studied showed the opposite pattern: apparent small intestinal absorption was larger than total intestinal absorption, suggesting that the caecal–colon region takes part in mineral turnover.