agricultural production guidelines
dairying in kwazulu-natal
Dairying in KwaZulu-Natal
Dairying 5.3 1995
VITAMIN NUTRITION OF DAIRY CATTLE
R M Bredon & T J
Cedara Agricultural Development Institute
Twenty-one minerals are
considered to be nutritionally essential, or probably essential, to the animal. Depending
on the quantities required by the animal, they can be grouped into major minerals and
trace (minor) elements. Of the major minerals the most important are calcium, phosphorus,
sodium, chlorine, potassium, sulphur and magnesium. The important trace elements are
copper, cobalt, iron, iodine, zinc, manganese and selenium. Most of the major minerals and
trace elements are widely distributed in the herbage and the other feeds eaten by the
animal, and occur in sufficient quantities to meet animal requirements. Balanced
commercial feeds usually contain sufficient minerals to meet the needs of dairy cows under
However, the possibility of
clinical, or more likely subclinical, mineral deficiencies may occur even if conditions
deviate from the "typical". Clear-cut and well-defined symptoms can usually be
observed if an animal suffers from a clinical deficiency of a mineral. On the other hand,
subclinical deficiencies could adversely affect the rate of growth and the level of
production without causing obvious deficiency symptoms. Apart from actual mineral
deficiencies, mineral imbalances may also occur. These imbalances, through interaction,
can induce deficiencies by the formation of insoluble compounds which cannot be utilized
by the animal.
Mineral deficiencies, and
in some cases imbalances, cause metabolic disturbances and can produce specific deficiency
diseases. Fertility, and hence calving percentage, can be affected. Milk production is
obviously dependent on the health and the well-being of the dairy cow and any metabolic
disturbance will affect milk production.
low-producing animals will not require the same amounts of minerals as high producers.
Therefore deficiencies which are subclinical in low producers, often become clinical in
high-producing animals. Often the farmer is unaware of the existence of mineral
deficiencies, and it is not easy, nor is it always possible, to diagnose a deficiency of
any particular mineral. Improved live-mass gains or increased milk production in
apparently healthy animals often have been demonstrated when their feeds were supplemented
with minerals. These responses occurred when no evidence of a deficiency existed but,
judging by the beneficial effect of mineral supplementation, there must have been a
So far, the emphasis has
been on mineral deficiencies, but it must not be forgotten that an excess of some minerals
can also have a disastrous effect on the animal. There are well-known areas in the world
where cattle cannot be kept because of a high selenium concentration in the soil, and
hence in the herbage, which is toxic to the animal. An excess of molybdenum, as a result
of over-application to a pasture, can render the pasture unusable for many years. An
induced copper deficiency is caused by excessive soil molybdenum. Excesses of copper,
iodine or fluorine can also be very toxic to animals. The problem is very complex, and if
considerable care is not exercised when supplementing feeds with minerals, especially
trace elements, more harm than good can result.
The interactions between
individual minerals will be discussed in groups rather than separately. Those minerals,
major and trace, which are problematic in KwaZulu-Natal, and elsewhere in South Africa,
are discussed in this guide. Calcium, phosphorus, magnesium and salt (sodium and chlorine)
are deficient under specific conditions in KwaZulu-Natal. Of the trace minerals there is a
confirmed iodine shortage in the KwaZulu-Natal Midlands and there are known to be
incidences of copper and selenium deficiencies, and possibly of zinc.
The mineral requirements of
different classes of dairy animals will be found in the KwaZulu-Natal Dairy Leaflet 5.12
and licks recommended for different pastures in the Appendix Tables to this leaflet.
CALCIUM (Ca) AND
The dairy cow is more
likely to suffer from a lack of both calcium and phosphorus than from a lack of any other
mineral with the possible exception of salt. Strong homeostatic mechanisms exist which
regulate the absorption of calcium, i.e. only sufficient is absorbed to meet the
animal's requirements. The high-producing dairy cow is unable to obtain her calcium and,
to a lesser extent, her phosphorus requirements from dietary sources in early lactation.
This may be due to a low absorption capability carried forward from the dry period,
especially if high levels were fed during the latter stages of the dry period. The
skeleton (bones) provides a substantial reserve of Ca which the cow is able to utilize to
meet her requirements.
Two aspects must be
considered when discussing these two minerals, viz. deficiencies, and the ratio of
calcium to phosphorus in the diet.
Half of the dry mass of the
skeleton and the teeth is made up of calcium and phosphorus in the ratio of approximately
2 to 1. Blood also contains these minerals; there is about 10 mg of calcium and 15 mg of
phosphorus in each 100 ml of blood. Milk contains approximately 9 g of Ca and 7 g P per
Although there is only a
small amount of calcium (only 1% of the total calcium) in the soft tissues of animals, it
is essential for blood clotting, control of the heartbeat, membrane permeability and as a
co-factor in many enzymatic reactions. Phosphorus is a structural part of several body
proteins, phospholipids and nucleic acids. It is implicated in carbohydrate metabolism,
forming compounds with certain metabolic products. These phosphorus compounds take part in
the storage and release of energy for muscular work and for maintaining body temperature.
unthriftiness, decreased milk production, poor conception and pica (depraved appetite) are
the general symptoms of calcium and phosphorus deficiency. A young animal in advanced
stages of deficiency develops rickets (bones bend under the weight of the animal and,
owing to the pull of muscles, they become deformed), while older animals develop
osteomalacia (the same condition as rickets, but because adult bones are solid they
fracture instead of bending). In both cases, the unequal deposition of calcium and
phosphorus which takes place makes the symptoms very characteristic. The ends of long
bones become thicker and the middle becomes thinner. The animals suffer from stiffness of
the joints and develop lameness.
Rickets and osteomalacia
are also associated with vitamin D deficiency, and sometimes a magnesium deficiency.
Vitamin D acts as a regulator in the deposition of minerals in bone.
The first symptom of
calcium and/or phosphorus deficiency is poor conception. Animals are erratic in coming on
heat, the heat is often difficult to detect, and the animals do not conceive. Calcium
supplementation of kikuyu pasture, which is low in calcium, has been shown to alleviate
It has also been shown
experimentally that a shortage of calcium in the diet can reduce milk production by as
much as 4,5 litres per day over the whole of the lactation.
CALCIUM TO PHOSPHORUS RATIO
In Holland, after the
second world war, an attempt was made to restore soil fertility through very high levels
of fertilization. This excessive fertilisation resulted in multiple mineral deficiencies
and imbalances. The following conditions were found in cattle that were fed diets with
unbalanced calcium to phosphorus ratios:
Cattle, when walking,
placed their hind legs unnaturally far forward under the body and when standing, showed
sickle hocks. Their walking pattern caused the toes to become too long and the soles of
the feet became easily bruised, resulting in the development of dry or purulent corns.
Sometimes the inflammation penetrated up to the hoof joints. These were caused by a
surplus of phosphorus but a shortage of calcium.
The legs of cattle showed
a rickety appearance. When standing, there was a narrow stance in the hocks; the hocks
were too far behind the bodies, with the tails between the hocks which were usually soiled
with faeces. The gait of the cattle lacked smoothness and was hesitant. These were caused
by a surplus of calcium but a shortage of phosphorus.
Both of these conditions
have been observed in KwaZulu-Natal. The symptoms of excess phosphorus but calcium
shortage are not uncommon in cattle grazing kikuyu pastures. The addition of feed lime to
the mineral lick seems to clear up this condition. It has been observed that the
improvement in stance and gait coincides with an improvement in fertility and, in some
cases, improved milk production. The British Agricultural Research Council (ARC)
recommends a dietary Ca:P ratio of between 2:1 and 1:1. However, it has been shown that as
long as the ratio is not more than 3:1 there is no adverse effect on fertility.
Field experience in South
Africa showed a considerable increase in foot problems and a decrease of feed intake where
the ratio of Ca:P in the ration was less than 1:1.
The type of roughage, and
the type of concentrates must be considered when supplementing calcium and phosphorus to
achieve a correct ratio in the total ration.
The following are examples
of calcium to phosphorus ratios, in typical roughages and concentrates fed to lactating
||0,1 Ca : 1 P
||> 0,1 Ca : 1 P
(0,01 to 0,02% Ca : 0,2% P)
||0,5 to 1 Ca : 1 P
||5 to 7 Ca : 1 P
||3 to 4 Ca : 1 P
Typically, roughages in
South Africa contain between 1 Ca: 1 P and 1,2 Ca: 1 P; with phosphorus ranging between
0,2% and 0,35% on a dry matter basis.
of the lactating cow
The following daily
requirements of dietary phosphorus were recommended by the Agricultural Research Council
Milk production: 1,75 grams/kg of milk
(in addition to maintenance).
Pregnancy: 4 to 6 months 2,5 grams
6 to 7 months 6,5 grams
7 to 9 months 10,5 grams
Calcium requirements of
the lactating cow
It is suggested that the
optimum ratio of calcium to phosphorus is between 1,3:1 and 1,5:1. The latter ratio is
recommended by the National Research Council (NRC). The requirements for phosphorus can be
multiplied by a factor of 1,3 to 1,5 to obtain the amounts of calcium required.
Sources of Calcium and
|Bone meal (steamed)
*(These are approximate
supplements sold under various brand names contain varying amounts of different minerals
and the labels should be studied to determine the actual content. However, commercial
mixed rations do not carry sufficient information for practical ration formulation.
Usually only the maxima and minima of mineral constituents are stated. For example the
calcium concentration of commercial protein supplements was found to vary from 2 to 5%.
DISEASES ASSOCIATED WITH
CALCIUM AND PHOSPHORUS DEFICIENCIES
Milk fever is characterised
by symptoms such as muscular spasms, paralysis, and a loss of consciousness leading to
coma and death. These conditions are associated with an abrupt drop in the level of
calcium in the blood, which is not necessarily caused by a dietary deficiency of calcium.
Rather, it is due to the disfunctioning of the parathyroid glands. The efficiency of these
glands, which regulate the absorption of calcium through the production of calcitonin,
decreases during the dry period of the cow, when her requirements are much less than that
normally supplied by the feed during that period. The absorption of dietary calcium and
phosphorus during the early stages of lactation is often poor owing to low levels of
calcitonin, when the requirement of the cow for these minerals is high, as a result of
high milk production.
Reducing the calcium level
in the ration during the last three weeks of the dry period seems to stimulate the
parathyroid gland to produce calcitonin and consequently decreases the incidence of milk
fever by improving calcium absorption. There is considerable evidence that intramuscular
injections of vitamin D3 (0,4g) given 7 days before calving were effective in
preventing milk fever. If calving did not take place within the 7 days a second injection
Pica (depraved appetite)
This condition occurs in
animals deficient in phosphorus. They develop an unspecified craving, and consume foreign
material such as soil, flesh, wood or bones.
This disease occurs when
animals deficient in phosphorus start chewing bones infected by this bacterium during the
putrefication of flesh that was attached to the bones. The toxin produced by this
bacterium is fatal to animals.
Magnesium is a structural
part of bone and is closely associated with calcium, phosphorus and vitamin D in bone
formation. Magnesium is one of the activators in phosphorus metabolism. It is also
involved in carbohydrate metabolism and plays a major role in the neuromuscular functions
of the muscles. Although there are reserves of magnesium in bone and soft tissue, the
speed of mobilization of these reserves when required, is slow and of little help in an
emergency, e.g. in cases of grass tetany.
Two types of magnesium
deficiency are known in cattle:
Calves, fed milk only
(which is low in magnesium) for a long period, develop skin lesions, nervous muscular
irritability and, eventually, convulsions leading to death.
Older animals develop
grass tetany. Grass tetany often occurs in spring when animals are put out on lush young
grass after winter feeding, especially if the pasture was heavily fertilized with ammonium
sulphate. The symptoms which develop resemble those of milk fever, but the animals show
more acute excitability, they stagger (grass tetany) and have convulsions. An injection of
a calcium or magnesium salt, such as magnesium sulphate (epsom salts), will result in
quick recovery, but if this is not followed by further injections, or oral feeding of
magnesium, the tetany will reappear. This is not normally the case with milk fever. Care
must be taken when treating these animals because even a needle jab can trigger off
Calcium and magnesium salts
are interchangeable to a certain extent, and either one can often be of help in the
treatment of milk fever and of grass tetany. Large amounts of potassium from herbage,
however, can be antagonistic to calcium and magnesium absorption. There is some evidence
to suggest that the ionic balance between potassium (K) and calcium plus magnesium is
critical and should not exceed 2, i.e. K/(Ca + Mg) should be less than or equal to
2. Excessive sodium intake also may cause hypomagnesaemia, because increasing sodium
and/or potassium has been shown to decrease the apparent absorption of magnesium from the
gastro-intestinal tract, and to decrease the blood magnesium concentrations of cows. These
effects are particularly pronounced at high potassium intakes.
In sharp contrast to other
elements, the magnesium in lush green grass is not readily available to the animal. Many
dietary factors have been implicated in impairing the absorption of magnesium, namely,
sodium (both deficiencies and excesses), high nitrogen, excessively high calcium,
long-chain fatty acids, high rumen pH, low dry-matter content in rumen digesta, and
Kikuyu pastures which are
several years old accumulate considerable amounts of potassium from animal excreta and
usually have a low calcium content. It is likely that, in these high potassium, low
calcium pastures, there could be a shortage of both calcium and magnesium. The addition of
magnesium to the lick could be of advantage, especially during spring. Sub-clinical
deficiencies of magnesium have been demonstrated to cause lowering of milk production, and
the addition of magnesium could enhance milk production. It is suggested that the
supplementation of 4 to 6 g Mg per day to cows on pasture could be beneficial, e.g.
7 to 10 kg magnesium oxide per 100 kg lick fed at the rate of 100 grams per cow per day.
Both calcium and magnesium supplementation have been shown to alleviate fertility problems
in cattle grazing on kikuyu with high potassium and low calcium-plus-magnesium levels.
Magnesium requirements per
cow per day are approximately 9 g for maintenance, and an additional 0,74 g per litre of
milk. For a cow yielding 20 litres of milk the total requirement for magnesium therefore
would be 24 grams.
Potassium is the third most
abundant mineral element in the animal body. It is a major intracellular cation and is
involved in the osmotic regulation of tissue fluids and in acid-base balance. An ionic
balance exists amongst K, Na, Ca and Mg.
The requirements for K by
ruminants is estimated to be between 0,5 and 0,8% of the diet. The potassium requirement
appears to be increased by stress. Research has shown that the potassium requirements for
heat-stressed dairy cows increases to approximately 1,1%. Levels higher than 1,5% have
been associated with decreased dry matter intakes. Grass contains high levels of potassium
and deficiencies therefore are uncommon in grazed stock. High potassium levels in
well-fertilized pastures can be a problem, especially with regard to Mg absorption. The
maximum tolerable level for K is suggested to be 3% of the total dietary dry matter,
although surpluses are readily excreted in the urine.
An excess of potassium can
aggravate a sodium deficiency, depressing sodium levels by 30 to 60 %. This may be
particularly serious on kikuyu pastures, which are inherently low in sodium.
Pastures high in potassium,
particularly kikuyu, are a cause for concern in KwaZulu-Natal. Kikuyu pastures containing
potassium levels in excess of 5 % have been implicated in cases of bloat and of
infertility. Sodium has been shown to reduce the incidence of bloat on kikuyu pastures. It
should also be borne in mind that bloat may also be due to high levels of protein in the
herbage (in excess of 30% CP/kg DM in some cases). Some cases of infertility have been
shown to be reduced by supplementation with calcium and magnesium.
SODIUM AND CHLORINE
Sodium is a major
extracelluar cation and plays an active part in regulating the neutrality of blood serum.
Considerable amounts of sodium appear in the muscles and it is associated with their
A shortage of sodium
adversely affects utilization of both digested proteins and energy, and also prevents
reproduction. A shortage of sodium has been associated with cases of bloat on kikuyu
pastures that were heavily fertilized with nitrogen. High levels of potassium have been
shown to depress the concentration of sodium in plants. Pastures contain several times
more potassium than sodium, thus cows on pastures require more salt than do cows on dry
feeds or complete feeds. At a given potassium intake level, increasing the sodium intake
increases the sodium and decreases the potassium concentrations in the rumino-reticulum
digesta. Increased sodium levels have also been shown to be antagonistic to magnesium
The chlorides of the blood,
consisting mainly of sodium chlorides, make up more than half of the acidic ions.
Consequently the chlorides have a principal effect on the acid-base relationship. Chlorine
is connected with the formation of hydrochloric acid, an acidic secretion in the abomasum
of ruminants. Both sodium and chlorine are contained in the salt which is fed to animals
as a very important part of the mineral supplement. The ratio of sodium to chlorine in
salt is 1:1,6.
Salt deficiency in cattle
results in lack of appetite, rapid loss of weight and a decline in milk production.
Animals show unco-ordinated movements, a stiff walk, they shiver and are weak. Complete
collapse and death is known to occur in high-producing cows. Calves, in addition to the
general unthrifty condition, develop harsh coats.
The salt deficiency becomes
more pronounced during hot weather because of the loss of salt in perspiration. Kikuyu,
paspalum, sorghum, maize, tall fescue, lucerne and red clover are natrophobic (accumulate
sodium in the roots and not in the stem and leaf) plants and animals grazing these plants
require greater salt supplementation than is required for other plant species.
The recommended quantities
of sodium to be fed are 8,5 g for maintenance of a 500 kg cow plus 0,63 g for the
production of each litre of milk. This, allowing for salt impurities, is equivalent to
approximately 20 to 25 g of salt for maintenance plus 1,6 g per litre of milk. Chlorine is
more abundant in feeds than is sodium and there is no evidence of a chlorine shortage in
dairy rations. Consequently, the extent of supplementation must be based on sodium. Only a
small amount of the required sodium will be met from the ration, therefore most of it
should be supplied as salt. Provided that cows receive enough water, they have
considerable tolerance to salt. Consequently a small excess of salt, especially in summer,
might be of advantage.
Sulphur occurs in the
animal's body mainly in the sulphur containing proteins, that is, proteins which have the
amino acids cystine and methionine as part of their molecular structure. Some
"B" vitamins and the hormone insulin, also contain sulphur. A deficiency of
sulphur is seldom a problem if protein levels in the rations are high.
Sulphur is the most
important mineral for the proper development and maintenance of ruminal microflora,
because it may limit the synthesis of both cystine and methionine which are essential for
the synthesis of microbial body-proteins.
Symptoms of sulphur
deficiency are not very specific and are not easy to diagnose. Lower dry matter intake,
loss of weight, slow growth of wool in sheep, and sometimes death, are the symptoms of a
deficiency of this element. There is also a reduction in the microflora population
resulting in poor utilization of cellulose and poor protein synthesis.
The optimum level of
sulphur in the ration should be between 0,16 and 0,24% of sulphur. An excess of sulphur,
on the other hand, can be a factor contributing to copper deficiency, especially if the
ration has a high molybdenum content.
Iodine is found only in
minute amounts in the animal's body (less than 0,000 04%) but it is essential for normal
development. Half of the total amount of iodine is present in the thyroid gland and is
essential for the formation of thyroxine which is a secretion of this gland. A lack of
this secretion lowers basal metabolism and the thyroid gland then fails to control the
rate of body metabolism. The animal body tries to increase secretion of this gland by
enlarging it. This enlargement is called a goitre.
Iodine deficiency occurs in
areas where the water and feed are deficient in iodine. Goitrogenic (producing goitre)
feeds such as brassicas (e.g. rape, kale, turnips, cabbage) will aggravate a
deficiency. Star grass and clover can cause an indirect iodine deficiency through the
production of cyanogens.
In calves, deficiency
symptoms are stunted growth, an enlarged thyroid gland, apathy, blindness, hairlessness
and a harsh coat. Calves born to cows suffering from iodine deficiency will have enlarged
thyroid glands. If dissection of a full-term calf, either born dead or which dies soon
after birth, reveals a thyroid with a mass of over 8 g, then an iodine deficiency is
indicated. A thyroid mass of over 20 g in calves is not uncommon in KwaZulu-Natal.
In cows, an iodine
deficiency results in retained placentas and also impairs reproductive performance. Any
one, or more, of the following symptoms occuring in cows can indicate an iodine deficiency
(infertility usually occurs at early stages of a deficiency):
development at any stage of pregnancy leading to death of the foetus
the birth of a hairless
irregular or suppressed
In bulls, symptoms are a
decline in sexual vigour, and a deterioration in semen quality.
In iodine deficient areas
such as the KwaZulu-Natal Midlands, the supplementation of 120 mg/kg of iodine in the lick
seems to be required. It has been observed that, when only 90 mg/kg was present in the
lick, the occasional calf was stillborn and had an enlarged thyroid gland. These cases
seemed to disappear when the amount of iodine in the lick was increased from 90 mg/kg to
To achieve 120 mg/kg iodine
in the lick, 15,6 g potassium iodide or 20,2 g potassium iodate must be added to 100 kg
lick, or per 20 kg salt which will be mixed in the lick. Potassium iodate has the
advantage over potassium iodide in that it has greater stability. The aforementioned
amounts can be dissolved in approximately 1 litre water and sprayed over the salt, which
must be spread out. The best spray to use is a hand mist spray of the type sold in garden
shops. It is critically important that the iodine be thoroughly dispersed throughout the
lick mix, because iodine in large quantities is extremely toxic. Just about the only way
of thoroughly mixing the very small quantities of potassium iodate or iodide required, is
the method of dissolving and spraying over salt, described above. Alternatively,
commercial iodine pre-mixes are available which contain small amounts of iodine in a
carrier and can be conveniently mixed into a lick. The amount of iodine per package of
pre-mix should be checked, and the appropriate amount mixed per bag of salt before mixing
in the remainder of the ingredients. For example, 25 g of iodine per package would mean
that, with a mix containing approximately 20% salt, one package of pre-mix per 42 kg salt
would yield a final mix of 120 mg/kg iodine as follows:-
120 mg/kg of iodine is
wanted in the final mix containing 20% salt.
Therefore, (100 x 120) ¸ 20 = 600 mg/kg of iodine wanted in salt.
Now, 1 000 000 g salt must contain 600 g iodine, and 1 pack pre-mix contains 25 g iodine.
Therefore: (1 000 000 x 25) ¸ (600 x 1000) = 42 kg salt per pack pre-mix.
50 / 42 = 1,2 packs pre-mix
per 50 kg salt.
Iodine requirements for
growing animals are 0,12 mg/kg dry matter of the diet and for pregnant and lactating cows
the concentration of iodine should be 0,8 mg/kg dry matter of feed.
deficiencies rarely occur in ruminants, they can cause many problems, because manganese is
associated with tissue respiration and affects both growth and reproduction. It stabilizes
calcium and phosphorus metabolism and therefore has an influence on bone formation. It
also affects the function of the endocrine organs, enhances fat utilization in the body
and counteracts fatty degeneration of the liver.
Heat cycles in cows and
heifers are difficult to detect (silent heat) and conception is poor. A deficiency of
manganese in pregnant cows causes weak legs in newly born calves.
High calcium and low
phosphorus levels in the ration seem to increase the requirement for manganese.
Manganese deficiencies have
been identified in the Highveld, KwaZulu-Natal, Cape Coastal areas, Western Cape, Northern
Cape and southern Namibia. The recommended dietary allowance for manganese is 40 mg/kg dry
Zinc is a structural
component of various enzymes. Some play a part in digestion and some act as activators to
other enzymes. Zinc also intensifies the effect of insulin by protecting it from
decomposition by insulinase, and influences the reproductive system. Most of the zinc in
an animal's body is contained in the skin, hair and wool.
A deficiency causes
parakeratosis. This disease is manifested by slow growth, skin lesions and hair loss.
Cattle can develop spots on the tender parts of the skin, not unlike those occurring
during photosensitization. Other symptoms of zinc deficiency in ruminants are inflamed
membranes of the nose and mouth. The reproductive efficiency of males is lowered. Hair
loss in cattle has been observed. Excessive calcium in the diet can affect absorption of
zinc, but, in general, deficiency in ruminants is rare.
Ruminants can tolerate high
levels of zinc, although feeding an excess of zinc (500 mg/kg DM) can produce toxicity,
the symptoms of which are sluggishness, loss of appetite and diarrhoea. Zinc deficiencies
have been identified in most of the regions of South Africa.
The recommended dietary
allowance for zinc is 40 mg/kg DM.
COPPER AND MOLYBDENUM
Copper, apart from being a
catalyst necessary for the absorption of iron into haemoglobin, participates in the
processes of pigmentation and keratinization of hair. It is a structural component of
certain proteins and an activator of various enzymes. It is also essential for the proper
development and function of rumen micro-organisms.
Any or several of the
following symptoms are common when the diet of cattle is deficient in copper:
In recent years molybdenum
has often been applied to soils to stimulate the growth of plants. This creates the danger
of a physiological copper deficiency which occurs if an excess of molybdenum is applied,
for example, in seed maize production in the Greytown area of KwaZulu-Natal.
Excessive copper can be
toxic to the animal. It accumulates in the liver for a time, and then large quantities are
released into the blood-stream, causing a haemolytic crisis associated with jaundice and
liver necrosis and, eventually, death. Cattle can tolerate diets containing 100 parts per
million in the dry matter, but larger amounts can only be tolerated for a short period of
time. Sheep and milk-fed calves are far more susceptible to copper toxicity than are adult
The copper requirement of
the mature cow is about 100 mg copper per day. The dietary concentration of copper should
be about 10 mg Cu/kg of dry matter.
In cases of suspected
deficiency the inclusion of 0,25 to 0,5% of copper sulphate in the mineral lick is
Molybdenum is a structural
component of the enzyme nitrate reductase, which reduces non-toxic nitrates to toxic
An excess of molybdenum
will cause accumulation of nitrites in the rumen, with resulting toxicity.
The other adverse effects
of excessive molybdenum such as its antagonistic effect on copper assimilation, by the
formation of insoluble compounds of copper-molybdenum sulphate, is well known. The
formation of these insoluble compounds induces a physiological copper deficiency.
black hair turning grey, swollen vulva, weakness from exertion, and stiffness are known
No deficiency of molybdenum
under natural grazing conditions has yet been recorded.
The molybdenum requirements
of grazing livestock are estimated to be 1 mg/kg DM, or less.
IRON AND COBALT
These trace elements have
one thing in common: their deficiency, apart from any other specific symptoms, will cause
anaemia. Iron is a structural part of haemoglobin (red blood cells) while cobalt is
necessary for synthesis of vitamin B12, a deficiency of which causes pernicious
Iron deficiency causes
anaemia which is characterized by the general appearance of malnutrition, and the very
unpronounced, and fewer, blood vessels in the whites of the eyes. Generally speaking, only
calves fed for a long time on large quantities of milk are liable to develop anaemia
because milk is a poor source of iron. The food eaten by ruminants weaned from milk is
abundant in iron, consequently the anaemia caused by iron deficiency is not likely to
Dietary allowances for
cattle are 30 mg Fe/kg DM for dry stock and 40 mg Fe/kg DM for pregnant and lactating
Cobalt is a structural part
of vitamin B12 and a lack of cobalt renders it impossible for the ruminal
microflora to synthesise vitamin B12. The ruminal microflora require cobalt to
be supplied on a continuous basis and therefore it is pointless to inject cobalt.
The symptoms of a cobalt
No direct evidence of any
cobalt deficiency has been found in KwaZulu-Natal, but the suspicion exists that a
sub-clinical deficiency could occur after a prolonged period of heavy rainfall.
Cobalt in excessive amounts
can be toxic and under practical conditions the daily intake of 220 to 275 mg of cobalt
per 100 kg live-mass will produce toxicity symptoms within 4 to 30 days. The symptoms of
A dietary concentration of
0,1 mg Co/kg dry matter should meet cattle requirements for cobalt. In cobalt-deficient
areas, the addition of 50 to 60 grams cobalt sulphate per 100 kg salt normally should be
sufficient to correct the deficiency.
Only recently has attention
been paid to animal requirements for selenium. Until 1957, selenium was not considered to
be essential for animal health and was known to be very toxic in areas where the grazing
contained more than three parts per million (3 mg/kg DM). However, over the last 20 years
it has been found to be an essential trace mineral. Diets deficient in selenium caused
liver necrosis in rats, muscular dystrophy in calves and lambs ("white muscle"
disease in calves and "stiff lamb" disease in sheep), scouring in calves in some
areas, and delayed clearing of the afterbirth in cows. Selenium is involved in the
mammalian antioxidant defence system, playing a stimulatory role in the immune response
and thereby improving disease resistance.
Selenium behaves in a
similar manner to vitamin E. It appears that in dairy cows an adequate intake of selenium
can compensate for an inadequate intake of vitamin E and vice versa. The symptoms
of deficiency are not necessarily caused by a dietary deficiency of selenium. Selenium,
however, cannot take over all of the functions of this vitamin, but the level of vitamin E
in the diet will affect the animal's response to the feeding of selenium.
High dietary concentrations
of sulphur, as well as the heavy metals such as arsenic, mercury, silver, copper and
cadmium have been shown to reduce the availability of selenium. Fertilization of the soil
with elemental sulphur or superphosphate could induce clinical selenium deficiencies in
animals in areas where marginal deficiencies exist.
Generally speaking, a range
of from 0,1 to 0,5 mg/kg Se in dry matter in the diet is acceptable to the animal. Diets
with less than 0,1 mg/kg would be likely to cause deficiency while those with more than
5,0 mg/kg would be likely to be toxic. Because of the very real danger of toxicity,
selenium is very seldom added to animal diets or to mineral mixtures; in some countries it
is illegal to do so. Selenium therefore should be used only where it is almost certainly
deficient, and only under expert guidance because of the very real dangers of toxicity.
The delayed clearing of the afterbirth, a symptom of a selenium deficiency, with resultant
metritis can often be avoided through the injection of 50 mg of sodium selenite 20 to 21
days before calving.
Minerals are essential to
animal health and production. Most minerals are present in the feed in sufficient
quantities to supply the animal's requirements. The general deficiency of both phosphorus
and calcium is a well-established fact in this country. In fact, most of the pioneering
work on phosphorus and calcium nutition was done in South Africa. Consequently, phosphorus
and calcium are usually supplied as supplements.
Deficiencies of other
minerals do not normally occur, or do not cause clinically recognizable symptoms, except
in certain areas, or only when a very limited variety of food is fed to the animal. This
does not mean that sub-clinical deficiencies do not occur, but our present knowledge of
these is very limited or non-existent. Appendix Tables 2 to 4 have been designed to give a
number of alternative mixes for specific roughage combinations and Appendix Table 1 for
different sources of major minerals. This appendix should be studied and the mix chosen
which fits both the roughages fed and the sources of minerals which are available.
It will be noted that all
of these mixes contain a proportion of commercial mineral sources. The reason for this is
that, with our present limited knowledge of trace mineral deficiencies, it is desirable to
include a small proportion of these minerals which are most conveniently supplied by
commercial mixes containing trace minerals in proportions that are assumed to be correct
in the light of present knowledge.
Salt is the only other
mineral which, invariably, must be supplied in addition to calcium and phosphorus, because
all of the roughages normally fed in this country are deficient in salt.
High-producing animals have
a much higher requirement for minerals than do low producers. Thus it is invariably the
high-producers that are the first to show signs of mineral deficiencies or imbalances.
Therefore, it is the high producers which should be watched for deficiency symptoms.
Most mineral deficiencies,
or imbalances, affect fertility, often producing specific symptoms.
Only by trying
supplementation with specific minerals, and by observing animal response can one be
certain of the existence of a deficiency or imbalance. Laboratory-determined imbalances in
blood, liver and kidney samples can give a good indication of deficiencies, but these
analyses are expensive, and, more important, with the exception of blood samples, for
practical purposes, are impossible in the producing animal. Blood samples (blood profiles)
on their own (except in the case of very few minerals) are difficult, if not impossible,
to interpret because of a lack of knowledge about interactions.
As the general levels of
dairy production per cow rise, it is likely that mineral deficiencies will become more
common and, if manifested by clinical symptoms, easier to diagnose. Nevertheless, even if
subclinical deficiencies are suspected, the indiscriminate supplementation of feeds with
minerals must be avoided, because raising mineral levels can cause not only toxicity (in
excess), but also the antagonistic effect of some minerals on others, can create
imbalances and induce physiological deficiencies.
If a deficiency is
suspected, then expert advice should be sought and if the deficiency is confirmed, the
suspected mineral can be added to the diet. In the author's opinion, if the mixes as
detailed in Appendix Tables 2 to 4 are fed, the only other mineral likely to be deficient
is iodine, but others, as discussed under the individual minerals, may be deficient in
METHODS OF SUPPLEMENTING
CATTLE WITH MINERALS
There are six common
methods of supplementing cattle with minerals:
offering free choice,
individual mineral sources in a cafeteria system
offering a mixture of
minerals as a lick
minerals mixed with concentrates
feeding a mixture of
minerals individually to cows
injections or oral dosing
slow-releasing bullets or
soluble inpregnated glass.
But these systems can be
Free choice of
individual minerals in a cafetaria system
This system is based on the
assumption that animals themselves instinctively know which minerals they need, and that
they will consume the required quantity. This theory has been disproved. Some cows will
take several times the quantity of minerals taken by other cows. If they followed their
requirements, individual intakes would be similar. Cows tend to eat the most palatable
minerals rather than the required minerals.
It is also known that when
deficient, cows can develop a perverted appetite for minerals, which can persist for the
remainder of their lives.
This method must be used
where no individual control is possible. The criticisms of this method are:
individual animals vary
considerably in their intake of the mixture
the mixture becomes
unpalatable after being exposed to dew or rain
if the lick troughs are
too small, bullying will occur, resulting in the prevention of free access to the lick for
Minerals mixed in
It is impossible to supply
accurately the required quantities of minerals by mixing them in a standard concentrate.
This is because the amount of concentrates given to individual cows varies with some cows
not receiving any concentrates and thus minerals. At lower levels of production, the cow
becomes more dependent on the roughages as its mineral source. Cows receiving no
concentrates are entirely dependent on the roughages to meet their mineral requirements.
The roughage can be, and generally is, deficient in some minerals. This means that,
whatever the level of minerals in concentrates, some cows will be overfed minerals while
others are underfed, because the minerals supplied are balanced for an average production
at an average concentrate supplementation level.
supplementation of cattle
An estimate is made of the
average production that can be expected from roughages alone. A mineral mix is made up to
balance the deficiencies in the roughages and this is fed to the individual cows in
measured or weighed amounts. In practice a tablespoon which holds about 50 g is a
practical tool for mineral supplementation. One to three or more spoonsful of the
supplement would be fed daily, either alone or on top of the cows concentrates. The
requirements for production above that obtained from the roughages are added to the
The advantages of this
system are that the stockman knows that each cow gets her requirements and is not
dependent on her appetite for minerals or on her rank in the pecking order. Furthermore,
cows getting little or no concentrates will still receive minerals and cows getting a lot
of concentrates need not be overfed minerals. The mineral content of the concentrate can
thus be adjusted for production needs and no attempt need be made to make up roughage
This method is the method
of choice for supplementation of macro-minerals such as salt, calcium, phosphorus and
magnesium etc. Specific micro-mineral deficiencies can be individually catered for
by injections or by slow-releasing bullets.
Injections and oral
Oral dosing, or drenching,
of animals with mineral solutions or pastes of the required minerals has the advantage
that all animals receive known amounts of the required mineral at known intervals. This
type of treatment could prove unsatisfactory where labour costs are high and the animals
must be handled frequently, specifically for treatment. Certain of the disadvantages
associated with the use of licks or oral drenches can be overcome by the use of injectable
organic compounds of the minerals. Such complexes are more expensive, but when injected
intramuscularly, are absorbed slowly into the tissues and provide protection against a
dietary deficiency of the injected element for lengthy periods.
Bullets and soluble
Heavy pellets (bullets) of
the mineral, or soluble glass which has the specific mineral impregnated into it, are
useful in supplying specific minerals, or minerals which need to be supplied continuously,
for lengthy periods. These lodge in the reticulo-rumen of sheep and cattle and yield a
steady supply of the mineral to the animal for periods of months or even years.
are complex organic compounds that function as parts of enzyme systems essential for the
transformation of energy and regulation of body metababolism, and are required in minute
amounts for normal growth, production, reproduction and/or health.
Vitamins A,D,K, E, C and
the B Group are essential to animal health. A considerable variety of these, namely all
the B vitamins and vitamin K, can be synthesized by the ruminal microflora. A deficiency
of vitamin B12 can occur, but only if cobalt is lacking. All green feeds are
rich in vitamin C and in carotene, the latter being the provitamin (precurser) to vitamin
A. Vitamin E occurs in most feeds, and it has been shown that a deficiency is most
unlikely to occur unless the diet is short in selenium. Vitamin C deficiency has never
been demonstrated in ruminants.
Vitamin deficiencies in
cattle are rare and supplementation is only required in certain specific circumstances.
This vitamin has two
primary functions in the animal body. First, it is essential for the maintenance of the
epithelium, which forms the protective membranes in the respiratory and digestive tracts,
and the lining of the eyes. If this vitamin is deficient, the epithelium becomes
keratinized and cracks occur, giving easy access to bacteria and viruses, resulting in
infectious diseases. Second, vitamin A plays an important role in the chemical processes
which occur in the eye and are essential for vision. This vitamin combines with proteins
in the retina of the eye and forms the pigment called visual purple. These cells, together
with the lens pigment, are responsible for vision in dim light. During this process, some
of the vitamin A is excreted and has to be replenished from the blood, if normal vision is
to be maintained. Vitamin A deficiency, in addition to causing malfunction in the
processes referred to above, also will cause changes in bone structure and will affect
reproduction by interfering with the production of sperm in males, and by causing
resorption of the foetus in females.
Carotene is converted with
varying efficiency to vitamin A by the animal body. Adult cattle are much better
converters than are calves, and Holstein-Frieslands are better converters than are
Jerseys. Cattle have the ability to store vitamin A. Adult cattle can store enough for up
to three months. On green feeds, which are usually rich in vitamin A, cattle are unlikely
to suffer a vitamin A deficiency. In cows, such a deficiency may occur only towards the
end of winter, and then only if no green forage is available at that time. Under these
circumstances, it might be advisable, towards the end of winter, to inject cows with one
to two million international units of vitamin A, followed by a second injection a month
later. Younger animals should be injected with smaller quantities, depending on the size
of the animal.
The symptoms of vitamin A
deficiency are scouring, low resistance to bacterial infection, stiffness of joints and
unco-ordinated movements, lesions around the eyes and dull watery eyes followed by night
blindness at more advanced stages. The fertility of cows is always affected. A shortened
period of gestation, a high incidence of retained placentas, stillbirths and abortions are
common symptoms. Often calves are born blind and their movements are unco-ordinated.
Vitamin D occurs in plant
material in the form of a provitamin which is converted in the animal body, when exposed
to sunlight, to vitamin D. Adult cattle, unless stall fed, will not be vitamin D
deficient. Calves, when kept for long periods under cover without being allowed exposure
to the sun, can develop rickets. The symptoms are the same as those observed in cases of
calcium and phosphorus deficiencies. Supplementation of the diet of calves with halibut or
cod-liver oil will prevent rickets.
Vitamin E, apart from its
other minor functions, has very strong antioxidant properties and is involved in the
mammalian antioxidant defence system where it stimulates the immune response, thereby
bringing about disease resistance.
For certain purposes, the
antioxidant functions of vitamin E can be performed by other antioxidants. Selenium for
example, which is present in glutathiozone peroxidase, decomposes peroxides, which are
toxic. This is one of the reasons for the interaction between vitamin E and selenium, and
in many cases either selenium or vitamin E can correct dietary deficiencies. For example,
it has been shown that the occurrence of muscular dystrophies (myopathinies, white muscle
disease) in cattle can be prevented by administering traces of either selenium or vitamin
E. Where, however, animals are getting a diet rich in unsaturated fatty acids (for
example, cod liver oil fed to calves) the addition of selenium to the diet will not help
muscular dystrophy, but the addition of vitamin E will be effective. Vitamin E, on the
other hand, will not be effective in cases where the selenium content of the diet is high
(above 0,08%). In herds where the incidence of retained placenta is high, injecting each
cow with selenium 21 to 25 days before calving is effective in reducing the incidence of
retained placenta, in such cases vitamin E has no effect.
The exact interrelationship
between vitamin E and selenium is not yet clear. However, a shortage of vitamin E is
unlikely to occur, because green roughages are sources of this vitamin. Maize is a poor
source, but wheat by-products (especially wheat germ) are excellent sources, of this
ARC, 1965. The nutrient
requirements of farm livestock. No. 2. Ruminants. London: Agricultural Research
ARC, 1980. The nutrient
requirements of ruminant livestock. Farnham Royal: Commonwealth Agricultural Bureaux.
GRACE, N.D., 1983. The
mineral requirements of grazing ruminants. (Occasional Publication No. 9): New Zealand
Society of Animal Production.
MAFF, DAFS, DANI, UKASTA,
BVA, 1984. Mineral, trace element and vitamin allowances for ruminant livestock, in: Recent
advances in animal nutrition, edited by Haresign W. & Cole, D.J.A.
McDOWELL, C.R., CONRAD,
J.K., ELLIS, G.L. & LOOSLI, J.K., 1983. Minerals for grazing ruminants in Tropical
Regions. University of Gainesville: Florida.
NRC, 1971. Nutrient
requirements of dairy cattle,. 5th ed. Washington D.C: National Academy of Sciences.
NRC, 1978. Nutritional
requirements of dairy cattle, 5th rev. ed. Washington D.C: National Academy of
APPENDIX TABLE 2
APPENDIX TABLE 3
APPENDIX TABLE 4
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