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OCR for page 459
Strontium
Strontium (Sr) is one of the alkaline earth metals, and, because of its
high chemical activity, it never occurs free in nature (Pidgeon and
Preisman, 1969~. It occurs in nature principally in the minerals stronti-
anite (SrC03) and celestite (SrS041. The role of strontium in biological
systems received little attention until the late 1940's, when it became
obvious that 90SF is an abundant and potentially hazardous radioactive
by-product of nuclear fission.
ESSENTIALITY
Strontium has been reported to act as a plant growth stimulant
(Underwood, 1977) and to be capable of replacing the calcium required
by Chiorella (Walker, 1953~. It has not, however, been shown to be
essential for either plants or animals. A report by Rygh (1949) indicated
that the omission of strontium from the mineral supplement fed to rats
and guinea pigs consuming a purified diet resulted in growth depres-
sion, an impairment of the calcification of the bones and teeth, and a
higher incidence of dental caries. This work has not been confirmed.
METABOLISM
Early studies of the metabolism of strontium showed a close relation-
ship with calcium (Fay et al., 19421. It was shown that strontium be-
459
OCR for page 460
460 MINERAL TOLERANCE OF DOMESTIC ANIMALS
havior in mammals was similar but not identical to that of calcium. The
strontium ion (Sew) is very similar to the calcium ion (Ca+2), both
chemically and physiologically, and it can substitute for calcium in
physiological processes. These include muscular contraction, blood
clotting, and bone formation. One difference which has been observed
is that the rates of most of these processes are slowed when strontium
is substituted for calcium. The major differences between strontium
and calcium behavior were found relative to gastrointestinal absorp-
tion, renal excretion, lactation, and placental transfer. It appears that
whenever there is a metabolically controlled passage of ions across a
membrane, calcium is transported more effectively than strontium
(Comer and Wasserman, 19641. Once absorbed, the element has a
strong affinity for the skeletal system. Strontium is poorly absorbed by
adult animals on natural diets, with a large proportion of the ingested
strontium appearing in the feces.
SOURCES
There is limited information on the normal intake of strontium by farm
animals. With ruminants, this will be influenced by the strontium status
of the soil and by the proportion of legumes to grasses in the herbage
consumed. Mitchell (1957) found red clover growing on different soils
ranged from 53 to 115 (mean 74) ppm strontium and ryegrass from 5 to
18 (mean 10) ppm strontium (dry basis). Strontium compounds are not
added to animal diets and would occur in such diets as contaminants of
other ingredients.
TOXICOSIS
Strontium (Sr+2) is less toxic than calcium (Ca+21. When strontium is
fed along with low levels of calcium to young or growing animals, bone
formation is disturbed and a condition known as "strontium rickets"
develops (Bartley and Reber, 1961; Colvin and Creger, 1967; Colvin et
al., 1972~. It has also been reported that strontium in the diet gives rise
to insoluble phosphates during digestion and to a phosphorus de-
ficiency (Jones, 1938~. The rachitogenic action of strontium is probably
related to the levels and ratio of calcium and phosphorus in the diet.
Knight et al. (1967) fed growing beef cattle diets containing two levels
of calcium (0. 13 and 3.1 percent) and three levels of strontium (13, 200,
and 2,000 ppm) for a 100-day period. High-calcium diets reduced weight
gains and the digestibility of both dry matter and energy. The various
OCR for page 461
Strontium
461
strontium levels had no effect on these criteria. The amount of stron-
tium in bone ash increased with each added increment of strontium in
the diet. The amount deposited was reduced by high-calcium additions.
Bartley and Reber (1961) reported on the toxic effects of strontium in
pigs (3 to 8 weeks old). Dietary treatments included 0.89 or 0.16 percent
calcium and "zero" or 6,700 ppm strontium. The pigs fed 6,700 ppm
strontium and 0.16 percent calcium were the most severely affected by
incoordination and weakness, followed by posterior paralysis.
Weber et al. (1968) fed dietary calcium levels of 0.72 and 1.0 percent
with 3,000 and 6,000 ppm strontium as SrCO3 to chicks. Feeding 6,000
ppm strontium reduced growth rate more severely at the lower calcium
level. Higher levels of strontium appeared to reduce calcium retention,
while phosphorus utilization was apparently unaffected. Higher levels
of strontium in bone ash were found at the lower calcium level.
In a later study, Doberenz et al. (1969) fed high dietary levels of
stable strontium to mature hens. Levels of 3,000 to 50,000 ppm of
strontium as carbonate were fed for a 4-week period. The diet con-
tained 2.9 percent calcium. The mature hen was able to tolerate con-
siderable amounts of strontium in the diet. Egg weight, egg production,
feed consumed, and body weights were unaffected by dietary levels up
to 30,000 ppm. At a dietary level of 50,000 ppm strontium, egg weight,
egg production, and feed consumed were significantly reduced.
TISSUE LEVELS
Gerlach and Muller (1934) found the strontium concentration of a wide
variety of animal tissues ranged from 0.01 to 0.10 ppm, with no evi-
dence of accumulation in any particular species, organ, or tissue. Stud-
ies have demonstrated that as dietary levels of strontium are increased,
the strontium absorbed is concentrated in the bones or skeletal system
and not the soft tissue. In a study of the strontium content of cow's
milk, Jury et al. ~ 1960) reported levels ranging from 31 to 65 ppm of the
ash, or approximately 0.2 to 0.4 ppm of the whole milk. A report by
Murphy et al. (1972) on samples of milk collected from cities in the
United States gave results in close agreement with those of Jury e! a].
(1960~.
MAXIMUM TOLERABLE LEVELS
The effect of strontium is very dependent on the dietary level of cal-
cium, with more pronounced effects observed at low-calcium levels.
When dietary calcium levels are at NRC recommended levels for the
OCR for page 462
462 MINERAL TOLERANCE OF DOMESTIC ANIMALS
respective species, animals have a high tolerance for strontium. Mature
animals can tolerate higher levels than the young. Assuming adequate
calcium, dietary strontium levels as high as 2,000 ppm (0.2 percent) can
be tolerated for extended periods of time, even by the young. Swine and
poultry can tolerate 3,000 ppm (0.3 percent) and the laying hen can
tolerate levels of 30,000 ppm (3 percent). Limited data indicate that
animal diets normally contain about 200 ppm strontium.
SUMMARY
Strontium is one of the alkaline earth metals, and, because of its high
chemical activity, it never occurs free in nature. It has not been shown
to be essential for either plants or animals. Strontium is metabolized
similarly to calcium by animals, and it can substitute for calcium in
physiological processes. When strontium is fed with low levels of cal-
cium to young or growing animals, bone formation is disturbed and a
condition known as "strontium rickets" develops. Assuming adequate
calcium, dietary strontium levels as high as 2,000 ppm (0.2 percent) can
be tolerated for extended periods of time? even by the young. Swine and
poultry can tolerate 3,000 ppm (0.3 percents, and the laying hen can
tolerate levels of 30,000 ppm (3 percent).
OCR for page 463
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OCR for page 465
Strontium
REFERENCES
465
Bartley, J. C., and E. F. Reber. 1961. Toxic effects of stable strontium in young pigs. J.
Nutr. 75:21.
Colvin, L. B., and C. R. Creger. 1967. Stable strontium and experimental bone anoma-
lies. Fed. Proc. 26:416.
Calvin, L. B., C. R. Creger, T. M. Ferguson, and H. R. Crookshank. 1972. Experimental
epiphyseal cartilage anomalies by dietary strontium. Poult. Sci. S1:576.
Comar, C. L., and R. H. Wasserman. 1964. Strontium, pp. 52~572. In C. L. Comar and
F. Bronner, eds. Mineral Metabolism, vol. 2. Academic Press, New York.
Doberenz, A. R., C. W. Weber, and B. L. Reid. 1969. Effect of high dietary strontium
levels on bone and egg shell calcium and strontium. Calcif. Tissue Res. 4:180.
Fay, M., M. A. Andersch, and V. G. Behrmann. 1942. The biochemistry of strontium.
J. Biol. Chem. 144:383.
Gerlach, W., and R. Muller. 1934. The occurrence of strontium and barium in human
organs and excrete. Virchows Arch. Pathol. Anat. Physiol. 294:210.
Jones, J. A. 1938. Metabolism of calcium and phosphorus as influenced by addition to the
diet of salts of metals which form insoluble phosphates. Am. J. Physiol. 124:230.
Jury, R. V., M. S. Webb, and R. J. Webb. 1960. The spectrochemical determination of
total strontium in bone, milk and vegetation. Anal. Chem. Acta 22:145.
Knight, W. M., V. R. Bohman, A. L. Lesperance, and C. Blincoe. 1967. Strontium
retention in the bovine. J. Anim. Sci. 26:839.
Mitchell, R. L. 1957. The trace element content of plants. Research (London) 10:357.
Murthy, G. K., U. S. Rhea, and J. T. Peeler. 1972. Copper, iron, manganese, strontium,
and zinc content of market milk. J. Dairy Sci. 55:1666.
Pidgeon, L. M., and L. Preisman. 1969. Kirk-Othmer Encyclopedia of Chemical Tech-
nology, vol. 19, 2nd ed. John Wiley & Sons, New York.
Rygh, O. 1949. Research on trace elements. 1. Importance of strontium, barium and zinc.
Bull. Soc. Chim. Biol. 31:1052.
Underwood, E. J. 1977. Trace Elements in Human and Animal Nutrition, 4th ed. Aca-
demic Press, New York.
Walker, J. B. 1953. Inorganic micronutrient requirements of Chlorella. I. Requirements
for calcium (or strontium), copper' and molybdenum. Arch. Biochem. Biophys. 46:1.
Weber, C. W., A. R. Doberenz, R. W. G. Wyckoff, and B. L. Reid. 1968. Strontium
metabolism in chicks. Poult. Sci. 47:1318.
Representative terms from entire chapter:
strontium strontium strontium
