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OCR for page 131
Calcium
Calcium (Ca), a white, silvery, alkaline earth metal, was discovered in
1808 by Sir Humphrey Davey. Its name was derived from the Latin
word cabs, a name by which the oxide of the element was known to
early Romans. Calcium does not occur in the free state, but its com-
pounds are widely distributed in nature. It is the fifth most abundant
element in the earth's crust and the most abundant cation in the animal
body, comprising 1 to 2 percent of the total weight. Approximately
99 percent of the calcium in the animal body is found in the bones and
teeth, with the remaining I percent widely distributed in venous soft
tissues. Calcium has a very close interrelationship why phosphorus and
vitamin D (Hegsted, 19731.
ESSENTIALITY
Calcium has been recognized as an essential element in animal nutrition
for et least 100 years. Quantitatively, the participation of calcium in the
formation of bone is its most important function. Bone acts not only as
a supporting or structural component of the body, but also as a vital
physiological tissue serving to provide a readily available source of
calcium for maintenance of homeostasis. The 1 percent of the body's
calcium outside of the bone functions in a number of essential pro-
cesses and is found in extracellular fluid, soft tissue, and as a com-
ponent of various membrane structures (Bronner, 19641. Calcium is
131
OCR for page 132
132 MINERAL TOLERANCE OF DOMESTIC ANIMALS
involved in blood coagulation; it is necessary for muscle contractility,
myocardial function, normal neuromuscular irritability, and integrity of
intracellular cement substances and various membranes. Calcium is
also an activator of numerous enzymes.
METABOLISM
There are many factors that influence the absorption, distnbution, and
excretion of calcium. Calcium is absorbed from the intestine by an
active transport mechanism. Vitamin D is required for this active trans-
po~t, and there is strong evidence that a vitamin D-induced, calcium-
binding protein plays a role (Wasserman and Corradino, 1973~. There
is evidence that the active transport of calcium is regulated to meet the
calcium needs of the body and is most active when dietary calcium is
restricted or when the needs are great such as during pregnancy, lac-
tation, and egg production (Wilis, 1973~. Calcium is also absorbed by
passive ionic diffusion, a process that may be vitamin D dependent.
The active process is believed to occur mainly in the proximal
duodenum and the passive process in the remainder of the small
intestine (Avioli, 19721.
The level of calcium in serum, maintained remarkably constant at a
concentration of about 10 mg/d} in most species, is regulated by para-
thyroid hormone (PrH), calcitonin, and metabolically active vitamin D.
It is believed that a slight decrease in serum calcium causes an
increased secretion of PTH. PrH stimulates the biosynthesis of
1,2S-dihydroxy vitamin D3, which causes an increased absorption
of calcium from the intestine and an increased resorption of calcium
from bone. On the other hand, a slight increase in serum calcium results
in a decrease in PTH secretion and an increase in calcitonin release.
These changes effect a decreased production of 1,25-dihydroxy vitamin
D3, causing a reduction in intestinal absorption and bone resorption of
calcium (Tanaka et al., 1973~.
Approximately 60 percent of the serum calcium is ionized and
physiologically active. The remaining calcium is non~on~zed and physi-
olog~cally inert; 35 percent of the serum calcium is bound to protein and
5 percent is complexed with citrate, bicarbonate, and phosphate (White
e! al., 1968~. A significant decrease in serum ionized calcium results
in tetany, while an increase can cause cardiac or respiratory failure
Trough an impairment of muscle function (Bronner, 1964; Goodman
and Gilman, 1975~. '
Calcium metabolism is influenced by a large number of factors.
.
OCR for page 133
Calcium
133
Several reviews have presented detailed discussions (Nicolaysen et al.,
1953; Rasmussen and DeI-uca, 1963; Bronner, 1964; Hegsted, 1973;
Borie, 1973, 1974; Mueller et al., 1973; Schraer et al., 19731.
SOURCES
Calcium is present in variable amounts in almost all feedstuffs (National
Research Council, 1971~. The calcium content of natural feeds varies
widely, depending upon the species of plant, portion of plant fed, and
stage of matunty. In general, grains such as barley, corn, rnilo, oats,
and wheat are very low in calcium, having levels ranging from 0.02 to
0.10 percent. Noniegume roughages such as grass hay and mature range
forages are intermediate in calcium content (0.31 to 0.36 percent), and
legume forages such as alfalfa and clover hay contain 1.2 to 1.7 percent
calcium.
Several supplemental sources of calcium are used in animal diets,
With the most common being ground limestone or calcium carbonate.
Other common sources include oyster shell, calcium sulfate, calcium
chlonde, calcium phosphates, and bone meal. These range in calcium
content from 16 to 38 percent.
TOXICOSIS
Calcium compounds ingested obey are usually not considered toxic.
The homeostatic mechanism of the animal tends to protect against the
absorption of excessive quantities of the element; however, because of
the interrelationship with other nutnents, especially phosphorus, the
feeding of high or excessive levels of calcium for extended periods of
time can have a detn mental effect on animal performance. Optimum
animal performance is linked very closely with calcium and phosphorus
levels in the diet. Most animals require a fairly narrow calcium-to-
phosphorus ratio~suaDy no wider than 2: 1; however, ruminants can
tolerate wider ratios than monogastr~c animals providing the phos-
phorus level is adequate. The quantitative aspects of the dietary
calcium-to-phosphorus ratios and subsequent animal performance are
discussed in several recent reviews (Beeson et al., 1975; Harms et al.,
1976; Pea, 19761.
Partur~ent paresis (milk fever) resulting from calcium deficiency is a
metabolic problem, primarily affecting high-producing dairy cows,
which is probably related to endocrine function (Beeson et al., 1975~.
OCR for page 134
134 MINERAL TOLERANCE OF DOMESTIC ANIMALS
Both the parathyroid gland and calciton~n-secreting cells of the thyroid
may be involved. Dietary calcium intake prior to and during early
lactation is important in influencing the capability of these glands to
respond appropnately to the sudden change in metabolic demands for
calcium imposed by lactation. Black et at. (1973) conducted a study
with dairy cows in which they compared a high- and a tow-calcium diet.
The high-calcium diet provided 150 g of calcium per cow daily, whereas
the low-calcium diet provided 25 g. The phosphorus intake was 25 g per
cow daily for each calcium level. They concluded that cows fed high-
calcium `diets depend primarily upon intestinal absorption of calcium,
whereas in cows receiving less calcium, the significance of the para-
thyroid hormones in maintaining proper blood calcium levels is greater.
They stated that the-long-term feeding of a high-calcium diet appears to
suppress the chief celds of the parathyroids, so that they are less able
to respond quickly to a hypocalcem~c condition.
Dowe et al. (1957) studied the effect of excessive dietary calcium on
growing beef calves. The animals were fed a diet that provided 12 g of
phosphorus per day. Calcium-to-phosphorus ratios of 1.3:1, 4.3:1,
9.1: 1, and 13.7: 1 were compared by the addition of ground limestone.
The two higher ratios depressed gain. Ammerman et al. (1963) reported
that a level of 4.4 percent dietary calcium caused a significant depres-
sion in protein and energy digestion by beef steers. Lewis et a]. (1951)
found that excess calcium and a ration borderline in phosphorus con-
tent reduced feed consumption and rate of gain of steer calves. The
long-term nutritional effects of excessive dietary calcium on bulls was
studied by Krook et al. (l971~. Relative intake varied from 3.5 times
recommended requirements in young bulls to 5.9 times in old bulls. It
was suggested that the excessive calcium intake resulted in hyper-
secretion of calcitonin with the result that normal bone resorption was
inhibited and bone mass increased. With adequate phosphorus,
ruminant animals have been observed to perform satisfactorily with
dietary calcium-to-phosphorus ratios between 1: 1 and 7 :1. Depressed
performance has been observed with ratios above 7:1, but these
effects were not as extreme as those below 1:1. Most investigators,
however, suggest that calcium-to-phosphorus ratios for ruminants
should be in the range of 1.5: I to 2: 1 (Beeson et al., 1975~.
Fontenot- et al. (1964) fed calcium-to-phosphorus ratios of 1: 1, 2: 1,
4: 1, and 8: 1 (0.3 percent phosphorus) to lambs with and without sup-
plemental zinc (100 ppm). When no supplemental zinc was fed, rate of
gain tended to be decreased at the higher calcium levels (4: 1, S: 1~. Feed
efficiency was depressed 9 percent when these high-calcium levels
OCR for page 135
Calcium
135
were fed (compared to 1:1~. In the zinc-supplemented groups, calcium
level had no such effect on rate and efficiency of gain.
Zimmerman e' al. (1963) conducted a series of experiments to deter-
m~ne optimum calcium and phosphorus levels for maximum body
weight gain, feed conversion, and metatarsal calcification of swine
2 to 7 weeks of age. High calcium levels in the diets reduced rate of
body weight gain. In general, calcium-to-phosphorus ratios of 1.6: 1 or
wider adversely influenced gains. High calcium levels in the diet (above
0.8 percent) reduced feed efficiency. The results of this work suggested
a maximum dietary calcium level of 0.S percent and a minimum phos-
phorus level of 0.6 percent for optimum performance and adequate
skeletal development of young swine. Combs et al. (1966) observed
that when the level of calcium was increased in the diet of young pigs
from 0.48 percent to 0.~8 percent and to 1.32 percent, average daily gain
and feed conversion decreased significantly. The highest level of
calcium decreased apparent digestibility of calcium and dry matter. The
skin disease, parakeratosis, can be induced by high levels of calcium.
Luecke et al. (1956) produced a 100 percent incidence of parakeratosis
in pigs on a diet with 1.5 percent calcium, 0.8 percent phosphorus, and
31 ppm zinc. The addition of 20 ppm of zinc to the diet essentially
eliminated the disease. Newland et al. (1958) stated that pigs fed high-
calcium diets had an accelerated rate of zinc metabolism, thereby
increasing the requirement for zinc. A more complete review of the
effect of dietary calcium levels in swine is presented by Peo (l976~.
Urbana (1960) determined that levels of calcium carbonate above
3 percent of the diet (1.2 percent calcium) had an adverse effect on the
body weight gains from a 4-week chick expenment. In a large-scale
broiler trial by Smith and Taylor (1961), significantly different growth
rate and feed conversion values were detected between groups fed
either 0.83 or 1.35 percent calcium with a phosphorus level of 0.52
percent for a 10-week feeding period, with the O.X3 percent treatment
being superior. Fangauf et al. (1961) fed chicks with diets containing
1.2, 2.0, 3.0, 4.5, and 6.5 percent calcium and concluded that broiler
diets should not contain over 2 percent calcium. Levels above this
significantly depressed feed intake and body weight gain and increased
mortality. Shane et al. (1969) reported on a growing pullet study show-
ing that levels of calcium above 2.5 percent fed between ~ and 20 weeks
of age would cause nephrosis, visceral gout, calcium urate deposits,
and high mortality. Parathyroid size and activity were reduced, along
with feed consumption and weight gains. They recommended that diets
should not contain more than 1.2 percent calcium for pullets under 18
OCR for page 136
136 MINERAL TOLERANCE OF DOMESTIC ANIMALS
to 20 weeks of age. There are conflicting reports on the eject of excess
calcium in the diet of laying hens. Gutowska and Parkhurst (1942)
repotted that a high level (3.95 percent) of calcium in the diet decreased
egg production and feed efficiency. There was no significant difference
In eggshell breaking strength or egg weight. MacIntyre et al. (1963)
reported that levels of dietary calcium up to 6 percent did not depress
egg production, feed efficiency, or egg weight. Hanns and Waldroup
(1971) also found that calcium levels up to 5 percent did not significantly
affect the rate of egg production, egg weight, eggshell thick ness, or feed
consumption per hen per day during the 4-month feeding period.
There is evidence that levels of calcium greater than 1 percent in the
diet may have an adverse effect on the growth of laboratory animals
(Davis, 1959~. Goto and Sawamura (1973) reported that rats fed high-
calcium diets (2.83 percent added calcium) had significant weight loss
and decreased absorption and retention of nitrogen when compared to
the control group (0.72 percent added calcium). Increasing the calcium
level in the diet (above 1 percent) can have a depressing effect upon the
utilization of other nutrients in the diet, including protein, fats, vita-
m~ns, the macrom~neral elements phosphorus and magnesium—and
Me trace mineral elements, especially iron, iodine, zinc, and manga-
nese (Davis, 19591. In those instances where the intake of these
nutrients is just adequate, increasing the calcium in me diet may have
a markedly adverse effect and may produce a deficiency of the other
nutrients.
There are many factors that influence the absorption, distribution,
and excretion of calcium (Church and Pond, 19741. The level of dietary
phosphorus, the ratio of calcium to phosphorus, and the level of dietary
vitamin D are the most important.
MAXIMUM TOLERABLE LEVELS
Many sources of calcium are inexpensive, and animals have a tolerance
for widely diffenng levels in the diet. This has often led to the neglect
of dietary calcium levels and their balance with other nutrients,
primacy mineral elements. Except for the laying hen, which has a high
requirement for calcium, it is inadvisable to maintain dietary calcium
levels much above 1 percent. Experiments with most species have
shown that optimum animal performance is obtained when the ratio of
calcium to phosphorus in the diet is in the range of approximately 1.5: 1
to 2: 1. If adequate amounts of phosphorus are included in the diet, then
a wider ratio of calcium to phosphorus can be tolerated. In ruminant
OCR for page 137
Calcium 137
animals, diets with a ratio of calcium to phosphorus as wide as 7: 1 have
performed satisfactorily; however, the phosphorus has been present at
levels weD above that which is considered a requirement level.
Assuming the presence of adequate levels of dietary phosphorus,
the foBow~ng calcium levels can be tolerated; however, depending on
the age and production status of the animal, even these levels may
reduce performance: cattle, 2 percent; sheep, 2 percent; swine, 1 per-
cent; poultry, 1.2 percent; laying hen, 4 percent; horse, 2 percent;
rabbit, 2 percent.
SU~AlRY
Calcium does not occur in the free state, but its compounds are widely
distributed and it is the most abundant cation in the animal body. It is
an essential element in animal nutrition and serves a principal role in
bone formation, as wed as a number of other physiological processes.
Primary factors that influence the metabolism of calcium include phos-
phorus, vitamin D, hormonal systems, and the age of the animal.
Calcium compounds ingested orally are usually not considered toxic.
The homeostatic mechanism of the animal tends to protect against the
absorption of excessive quantities of the element; however, because of
the interrelationship with other nutrients, especially phosphorus, the
feeding of high or excessive levels of calcium for extended periods of
time can have a detrimental effect on animal performance.
The addition of extra calcium to an otherwise adequate diet may
precipitate a deficiency of other essential elements, i.e., phosphorus,
magnesium, ~on, iodine, zinc, and manganese. In every case, it
appears that the injurious effect of the calcium is due to an interaction
rather than to a harmful effect of the calcium itself. Additional quanti-
ties of the respective elements wiB overcome the adverse effect of the
calcium similar to that observed by reducing the level of calcium in
the diet. A relationship also exists between high dietary calcium and the
utilization of protein and fat. Because of the intricate interrelations
between calcium metabolism and that of other nutnents, caution must
be observed when calcium supplements are being added to the diet.
OCR for page 138
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OCR for page 140
140 MINERAL TOLERANCE OF DOMESTIC ANIMALS
REFERENCES
Ammerman, C. B., L. R. Amngton, M. C. Jayaswal, R. L. Shirley, and G. K. Davis.
1963. Effect of dietary calcium and phosphorus levels on nutrient digestibility by
steers. J. Anim. Sci. 22:248.
Avioli, L. V. 1972. Intestinal absorption of calcium. Arch. Int. Med. 129:345.
Beeson, W. M., T. W. Perry, N. L. Jacobson, K. D. Wiggers, and G. N. Jacobson. 1975.
Calcium in Beef and Dairy Nutrition. National Feed Ingredients Association, Des
Moines, Iowa.
Black, H. E., C. C. Capen, and C. D. Arnaud. 1973. Ultrastructure of parathyroid glands
and plasma immunoreactive parathyroid hormone in pregnant cows fed normal and
0th calcium diets. Lab. Invest. 29:173.
Borle, A. B. 1973. Calcium metabolism at the cellular level. Fed. Proc. 32:1944.
Borle, A. B. 1974. Calcium and phosphate metabolism. Ann. Rev. Physiol. 36:361.
Bronner, F. 1964. Dynamics and function of calcium, pp. 341 4$4. In C. L. Comar and
F. Bronner, eds., Mineral Metabolism, vol. 2, part A. Academic Press, New York.
Church, D. C., and W. G. Pond. 1974. Basic Animal Nutrition and Feeding. D. C.
Church, Corvallis, Oreg.
Combs, G. E., T. H. Be'Ty, H. D. Wallace, and R. C. Crum, Jr. 1966. Levels and sources
of vitamin D for pigs fed diets containing varying quantities of calcium. J. Anim. Sci.
25:827.
Davis, G. K. 1959. Effects of high calcium intakes on the absorption of other nutnents.
Fed. Proc. 18:1119.
Dowe, T. W., J. Matsushima, and V. H. Arthaud. 1957. The effects of adequate and
excessive calcium when fed with adequate phosphorus in growing rations for beef
calves. J. Anim. Sci. 16:811.
Fangauf, R., H. Vogt, and W. Penner. 1961. Studies of calcium tolerance in chickens.
Arch. Geflugelk. 25:82.
Fontenot, J. P., R. F. Miller, and N. O. Price. 1964. Ejects of calcium level and zinc
supplementation of fattening lamb rations. J. Anim. Sci. 23:874.
Goodman, L. S., and A. Gilman. 1975. We Pharmacological Basis of Therapeutics, 5th
ed. The Macmillan Company, New York.
Goto, S., and T. Sawamura. 1973. Effect of excess calcium intake on absorption of
nitrogen, fat, phosphorus, and calcium in young rats. J. Nutr. Sci. Vitaminal. 19:355.
Gutowska, M. S., and R. T. Parkhurst. 1942. Studies in mineral nutrition of laying hens.
11. Excess of calcium in the diet. Poult. Sci. 21:321.
Harms, R. H., and P. W. Waldroup. 1971. The effect of 0th dietary calcium on the
performance of laying hens. (Research Notes) Poult. Sci. 50:967.
Harms, R. H., B. L. Damron, D. A. Roland, and L. M. Potter. 1976. Calcium in Broiler,
Layer and Turkey Nutrition. National Peed Ingredients Association, Des Moines,
Iowa.
Hegsted, D. M. 1973. Modern Nutrition in Health and Disease, 5th ed. Lea and Febiger,
Philadelphia.
Krook, L., L. Lutwak, K. McEntee, P. A. Hendrickson, K. Braun, and S. Roberts. 1~1.
Nutritional hypercalcitonism in bulls. Cornell Vet. 61:625.
Lewis, J. K., W. H. Burkitt, and F. S. Willson. 1951. The effect of excess calcium with
borderline and deficient phosphorus in rations of steer calves. J. Anim. Sci. 10:1053.
Luecke, R. W., J. A. Hoefer, W. S. Brammell, and F. Twerp, Jr. 1956. Mineral interre-
lationships of parakeratosis of swine. J. Anim. Sci. 15:347.
OCR for page 141
Calcium
141
MacIntyre, T. M., H. W. R. Chancey, and E. E. Gardiner. 1963. Effect of dietary energy
and calcium level on egg production and egg quality. Can. J. Anim. Sci. 43:337.
Mueller, W. J., R. L. B~ubaker, C. V. Gay, and J. N. Boelkins. 1973. Mechanisms of
bone resorption in laying hens. Fed. Proc. 32:1951.
National Research Council. 1971. Atlas of Nutritional Data on United States and
Canadian Feeds. National Academy of Sciences, Washington, D.C.
Newland, H. W., D. E. Ullrey, J. A. Hoefer, and R. W. Luecke. 19S8. The relationship
of dietary calcium to zinc metabolism in pigs. J. Anim. Sci. 17:886.
Nicolaysen, R., N. Eeg-~rsen, and O. J. Malm. 1953. Physiology of calcium metabm
lism. Physiol. Rev. 33:424.
Peo, E. R., Jr. 1976. Calcium in Swine Nutntion. National Feed Ingredients Association,
Des Moines, Iowa.
Rasmussen, H., and H. F. DeLuca. 1963. Calcium homeostasis. Ergeb. Physiol. 53:109.
Schraer, R., J. A. Elder, and H. Schraer. 1973. Aspects of mitochondrial function in
calcium movement and calcification. Fed. Proc. 32:1938.
Shane, S. M., R. J. Young, and L. Krook. 1969. Renal and parathyroid changes produced
by high calcium intake in growing pullets. Avian Dis. 13:S58.
Smith, H., and J. H. Taylor. 1961. Effect of feeding two levels of dietary calcium on the
grow~ of broiler chickens. Nature 190:12W.
Tanaka, Y., H. F=nk, and H. F. DeLuca. 1973. Role of 1,25 dibydroxy-cholecalciferol
in calcification of bone and maintenance of serum calcium concentration in the rat. J.
Nutr. lOQ:1569.
Urbanyi, L. 1960. Chicken feeding trials with diets containing sufficient phosphorus and
increasing amounts of calcium carbonate. Nutr. Abstr. 30:691.
Wasserman, R. H., and R. A. Co'Tadino. 1973 . Vitamin D, calcium and protein synthesis.
Vitam. Horm. 31:43.
White, A., P. Handler, and E. L. Smith. 1968. Principles of Biochemistry, 4th ed.
McGraw-Hill, New York.
Wills, M. R. 1973. Intestinal absorption of calcium. Lancet 1:820.
Zimmerman, D. R., V. C. Speer, V. W. Hays, and D. V. Catron. 1963. Effect of calcium
and phosphon~s levels on baby pig performance. J. Anim. Sci. 22:658.
Representative terms from entire chapter:
calcium levels
