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Diss Factsheets

Administrative data

additional toxicological information
Type of information:
experimental study
Adequacy of study:
supporting study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Follows basic scientific principles. Not a toxicological study, but provides supporting data to suggest the inorganic phosphates tested are well tolerated in the diets of mammals.

Data source

Reference Type:
High phosphorus intake depresses apparent magnesium absorption in pregnant heifers
Schonewille JT, Klooster AT & Beynen AC
Bibliographic source:
J. Anim. Pysiol. a. Anim. Nutr. 71 (1994), 15-21

Materials and methods

Type of study / information:
Information on the use of phosphates as food additives for animals.
Test guideline
no guideline followed
Principles of method if other than guideline:
Six heifers, 20-23 months old and weighing 490-590 kg, were used; they were 4.5-7months in gestation. Five were a cross of Friesian-Holstein and Holstein-Friesian, and one animal was of the Meuse-Rhine-Ijssel breed. The animals calved between one and 12 weeks after completion of the trial; there were no metabolic disorders around parturition. During the experiment, the heifers were housed in a stanchion barn.
The trial had a 31 X 30-day cross-over design and was preceded by a 14-day run-in period. The animals were randomly assigned to the order of the two treatments, i. e. a low (2.2 g P/kg dry matter) and a high P (6.4 g P/kg dry matter) ration. The heifers were weighed after the morning meal on the last day of each period.
GLP compliance:
not specified

Test material

Constituent 1
Reference substance name:
sodium hydrogenorthophosphate
sodium hydrogenorthophosphate
Details on test material:
- Name of test material (as cited in study report): disodium phosphate

Results and discussion

Any other information on results incl. tables

Weight gain was 550 g/day (SE 193.4) when fed the low P ration, and 435 g/day (SE 162.6) when fed the high P ration (n = 6). The difference in body weight gain was not statistically significant.

All three mineral balances (P, Mg and Ca) were positive, irrespective of dietary treatment which was expected as the animals were in gestation and gained weight during the experiment. The high P intake was associated with a significant increase in faecal P excretion. The percentage of apparent absorption of P was higher with the high P ration but the increase was not significant. Urinary P excretion was raised non-significantly by the high P intake. When the high P ration was given, the heifers retained significantly more P than after feeding the low P ration. Mg intake was 4% lower (p = 0.006) when the heifers were fed the high P ration. Despite the lower Mg intake, faecal excretion of Mg was increased afer feeding the high P ration, this effect being borderline statistically significant. This resulted in a significantly depressed apparent absorption of Mg during the high P intake. Consequently, urinary Mg excretion was significantly decreased at the high P intake. The high P treatment tended to lower Mg retention, but this effect did not reach statistical significance.

Applicant's summary and conclusion


The influence of phosphorus on the apparent absorption of magnesium by pregnant heifers was determined in a 31 X 30-days cross-over study with six heifers fed rations containing 5.4 g magnesium and either 2.2 or 6.4 g phosphorus/kg dry matter. Supplemental phosphorus was in the form of Na2HP0, and the low phosphorus ration was balanced for sodium by adding NaHCO,.
After feeding the high phosphorus ration, urinary magnesium excretion was significantly reduced from 10.3 to 8.8 g/day while apparent magnesium absorption dropped significantly from
29.9 to 24.5%. Extra phosphorus in the ration had no effect on calcium excretion. The dietary magnesium concentrations and the phosphorus level in the high phosphorus ration were higher than those generally occurring in practice, whereas the phosphorus concentration in the low phosphorus ration was lower. The somewhat unusual magnesium and phosphorus levels in the rations and the relatively small inhibitory effect of high phosphorus intake on apparent magnesium absorption may limit the practical relevance of the outcome of the present study. Nevertheless, the present data do indicate that high phosphorus intakes may enhance the risk for magnesium deficiency when concurrent intakes of magnesium are low.