Animal Husbandry and Nutrition Florida Agricultural
Mimeograph Series No. 59-11 Experiment Station
HIGH LEVEL FEEDING OF SOFT PHOSPHATE TO RATS
L, R. Arrington and C, B. Ammerman1
Soft phosphate with colloidal clay is one of the phosphatic materials
used as a source of supplemental phosphorus for livestock. This product
and other naturally occurring phosphates contain fluorine, and the amounts
fed must be controlled in order to avoid an excessive intake of fluorine.
The fluorine problem in livestock feeding has been reviewed by Mitchell
and Edman (3), and results of extensive work by Hobbs et al.(2) have been
reported. In a previous experiment in this laboratory (1), two percent
soft phosphate in the diet of rats did not produce any harmful effects.
The primary objective of this experiment was to study the effect of
continuous high level feeding of soft phosphate upon the longevity of rats.
Limited growth measurement and bone ash determinations were also a part
of the study.
Thirty nine weanling rats of the Long-Evans strain were used in the
longevity trial, and 28 rats were used in the growth and bone ash study.
All rats were fed from weaning on a diet of the following basal compo-
sition: ground corn, 32 parts; casein 15; sucrose, 35; vegetable oil, 5;
brewers yeast, 4; salt, 0.5; CCO03 O.4; alphacel, 2,6-5.5. Two levels
of soft phosphate (2.9 and 5.8 percent) were added to the basal diet to
provide two treatments. The 2..9 percent level was considered the con-
trol since it contributed phosphorus in amounts to provide a normal
intake of phosphorus. Growth measurements were made from weekly weights
through nine weeks at which time the rats were sacrificed for bone ash
determination. The ash was determined as percent in the dry bone follow-
ing 24 hours asking in a muffle furnace at 6000 C.
For the longevity study, rats were provided 5.8 percent soft phos-
phate in the diet listed above, and were fed this diet continuously
from weaning until they died. These rats were given approximately five
grams of fresh liver every two weeks as the only diet supplement.
In order to compare the effect of fluorine intake from soft phos-
phate with that from calcium fluoride, sixteen male rats were fed the
same diet containing calcium fluoride (CaF2) in amounts calculated to
provide an intake of fluorine approximately equal to that from soft
phosphate. The calculated fluorine content of the diet containing
soft phosphate was 0.075 percent and that in the ration containing
calcium fluoride was 0.068 percent. Rats in this trial were continued
1Arrington, Associate Animal Nutritionist; Ammerman, Assistant Animal
Nutritionist, Florida Agricultural Experiment Station.
on the experiment for 12 months and were not used in the longevity trial.
The life span of rats fed 5.8 percent soft phosphate is recorded in table
1. Although some of these animals died early, the number involved is prob-
ably not larger than should be expected from natural causes. If one assumes
the normal life expectancy of the rat to be twenty three to twenty five months,
it may be considered that these rats lived a normal life span. It is evident,
however, from the symptoms produced that fluorine in the product was available
and absorbed. The characteristic symptom of elongation of the incisor teeth
occurred in essentially all of these rats. Excessive incisor growth was
apparent after three to four months, and continued so that it was necessary
to clip one eighth to one quarter of an inch from the upper incisors at approxi.
mately bimonthly intervals. No other symptoms of fluorine excess were observed.
The rats receiving 2.9 percent soft phosphate were not continued on the experi-
ment beyond the growth period, and symptoms of fluorine toxicity were not
studied in this group.
Longevity of Rats Fed 5.8 Percent Soft Phosphate
Initial less than 13-15 16-18 19-21 22-21 25-27 28-30 31-33 over 36
No. Rats 12 months mo. moO moo mo. mo. mo. moo moO
39 3 1 7 5 7 5 5 2
Fluorine as calcium fluoride caused excessive incisor growth in only one
rat of the 16 fed calcium fluoride, and this was not observed until the rats
had been on experiment approximately 10 months. No deaths occurred in this
group during the 12 month experimental period. It has been observed that
fluorine in calcium fluoride is less toxic than that in certain other com-
pounds (3), and it may be presumed that the fluorine in soft phosphate is
more available or more soluble than that in calcium fluoride.
Growth and femur ash values for the rats fed two levels of soft phosphate
are recorded in table 2. The results represent averages for seven males and
seven females in each group. Weight gains of both groups were below normal,
and this may be attributed in part to the basal ration. The ration contain-
ing 5.8 percent soft phosphate promoted somewhat greater gains than that
containing 2.9 percent. If the generally poor gains could have resulted in
part from the fluorine intake, it may be pointed out that the higher level
of soft phosphate with its corresponding higher intake of fluorine had less
growth depressing effect than the lower intake.
Bone ash values were equal for the two groups and were equal to bone
ash values of rats fed a similar diet but with phosphorus supplied from
other sources (1),
Growth and Bone Ash of Rats Fed Two Levels of Soft Phosphate
Gain Bone Ash
2.9 .037 14 66 109 59.6
5,8 .075 14 72 116 60.6
Weanling laboratory rats were fed continuously until death on a diet
containing 5.8 percent soft phosphate, which supplied .075 percent fluorine.
The rats lived through the normal life expectancy with excessive*growth
of the incisor teeth as the only specific symptom of excessive fluorine.
Fluorine from calcium fluoride in amounts approximately equal to that
supplied by soft phosphate did not produce elongation of the incisors
equal to that from soft phosphate. The high level intake of soft phosphate
did not cause abnormal growth or bone ash.
1. Arrington, L, R., D. C. Bowen and D. C. Tomlin. 1957. Utilization of
Phosphorus from Different Sources by Rats. Animal Husbandry Mimeograph,
No. 57-6, Florida Agricultural Experiment Station.
2. Hobbs, C. S., R. P. Moorman, Jr,, J. M. Griffith, J. L. West, G. M. Merri-
man, S. L. Hansard and C. C. Chamberlain. 1954. Fluorosis in Cattle and
Sheep. The University of Tennessee Agricultural Experiment Station, Bulletin
3. Mitchell, H. H. and Marjorie Edman. 1951. The Fluorine Problem in
Livestock Feeding. Nutrition Abstracts and Reviews. 21: 787-80L.