An isotope method to determine availability of phosphorus in different phosphatic sources

Material Information

An isotope method to determine availability of phosphorus in different phosphatic sources
Davis, George K
Arrington, Lewis Robert, 1919-
Outler, Jason Curry, 1922-
University of Florida -- Dept. of Animal Husbandry and Nutrition
Place of Publication:
Gainesville, Fla.
Dept. of Animal Husbandry and Nutrition
Publication Date:
Physical Description:
4 leaves : ; 28 cm.


Subjects / Keywords:
Phosphorus in animal nutrition -- Florida ( lcsh )
Phosphorus -- Isotopes ( lcsh )
Phosphorus ( jstor )
Phosphates ( jstor )
Feces ( jstor )
government publication (state, provincial, terriorial, dependent) ( marcgt )
non-fiction ( marcgt )


General Note:
Animal husbandry & nutrition mimeograph series - UF Dept. of Animal Husbandry and Nutrition ; no. 57-7
General Note:
"June, 1957."
Statement of Responsibility:
George K. Davis, L.R. Arrington and Jason C. Outler.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
71303271 ( OCLC )


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Full Text

Animal Husbandry & Nutrition Mimeroraph June, 1957
Series No. 57-7


George K. Davis, L. R. Arrington and Jason C. Outlerl

The need for supplemental phosphorus in many livestock and

poultry rations has resulted in the use of many phosphatic ma-

terials to supply the needed phosphorus. The value of any phos-

phate supplement will depend upon several factors, but the actual

availability to the animal is an important measure of its value.

A number of methods are in use to evaluate utilization or avail-

ability. Most of these involve feeding the test material under

controlled conditions and determining growth and bone composition

of the animal. An isotope method has been designed which affords

a direct measure of absorption. The purpose of this report is to

describe the method and to give some preliminary results.


Three different compounds have been studied with this method.

'Reagent grade dicalcium phosphate (CaHP04) was used as the ref-

erence standard, and two feeding grade phosphates were compared

with the standard.

Samples of the test materials are sent to Oak Ridge either

for two weeks or for one month irradiation in the pile (graphite

reactor). The exposure to neutron (ny) bombardment converts

1Davis, Animal Nutritionist; Arrington, Assistant Animal Nu-
tritionist; and Outler, Assistant in Chemistry, Department of
Animal Husbandry and Nutrition.

phosphorus-31 to phosphorus-32 which is radioactive phosphorus.

Since labeled phosphorus is metabolized in the same way as

natural phosphorus, it may be used to measure quantitatively the

amount absorbed.

The irradiated material is administered to selected animals

which are confined to digestion stalls so that feces and urine

may be collected separately and quantitatively. The weighed

dose of the radioactive phosphate is administered in a capsule

with a balling gun. Fecal collections are made for six days,

samples are taken, digested and the radioactive phosphorus in the

feces is determined. The amount and activity of that administered

is known so that the amount present in the fecal excretion repre-

sents primarily that which has not been absorbed.

The amount of radioactive phosphorus in the feces subtracted

from that fed to the animal gives an approximate measure of the

phosphorus absorbed since the radioactive phosphorus is a part of

the phosphate compound that is being tested. Total phosphorus de-

terminations are made to provide the full information on comsump-

tion and excretion of phosphorus.

Some phosphorus is absorbed in the upper part of the intestine

and then reexcreted back into the digestive tract. This appears

in the feces as unabsorbed phosphorus. For a measure of total

absorbtion, it is necessary to measure the phosphorus which is

absorbed and reexcreted. This reexcreted phosphorus increases as

animals get older and is especially important for the evaluation

of phosphorus used for livestock and poultry after the very early


growing period.

A measurement of the phosphorus absorbed and reexcreted is

possible by use of the radioactive phosphorus. If the rate of

reexcretion does not change rapidly, then the same animal used

at two different periods can provide an estimate of the phospho-

rus excretion into the intestinal tract.

This measurement has been accomplished by injecting radio-

active phosphorus in phosphates into the blood of the animal.

The phosphorus is rapidly mixed with the blood and radioactive

phosphorus appearing in the feces is then a measure of the phos-

phorus excreted from the blood. Since the radioactive phosphorus

acts in the same manner as stable phosphorus and is a measured

proportion of blood phosphorus, this gives us a measure of total

phosphorus excreted that had been absorbed into the blood.

If the phosphorus, reexcreted from the blood, is similar for

all sources of dietary phosphorus, then fecal phosphorus compared

to consumed phosphorus may be used as an approximate measure of

absorbed phosphorus but the values will always be less than was

actually absorbed. Since this may not be true, experiments to

check this are being continued.

One of the questions which has been raised regarding this

method is whether or not irradiation in the pile changes the form

of the phosphate. If the amount of the ortho form is increased

or decreased during irradiation, the results would have to be cor-

rected to account for the change. Tests of the materials after

irradiation have thus far shown no change, but these are being



Preliminary Results
Preliminary Results

Comparative results using the three phosphates are recorded

in Table I. These data represent absorption which is calculated

by subtracting total fecal excretion from the dose administered.

If the values were corrected for that portion of phosphorus that

is absorbed and reexcreted, then the values would be somewhat



Reference (CaHP04)

Phosphate A

Phosphate B

% Absorbed by
Calves at 144 hours




% Absorbed by
Rats at 72 hours



These results should not be interpreted as conclusive but

as preliminary. Tests are being continued as facilities and ani-

mals become available.

. 1.