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Trace minerals
Six trace minerals have been shown to be needed as supplements in poultry diets:
iron, copper, zinc, manganese, iodine and selenium. Subclinical trace mineral
deficiencies probably occur more frequently than are recognized by poultry
producers. Some soils are naturally deficient in trace minerals. In addition, crops
and plants vary in their uptake of minerals. Consequently, feedstuffs grown in
certain geographic areas may be marginal or deficient in specific elements.
Certain areas in North America experience a high rainfall, which results in
leaching of the soil and selenium deficiency. As a result, selenium deficiencies
have been observed in livestock in Asia when fed US-produced maize and
soybean meal but not when fed locally grown feed. Feed suppliers are usually
aware of deficient (and adequate) levels of the trace minerals present in
feedstuffs
and
will
provide
trace
minerals
mixes
formulated
appropriately.Several studies have shown that omitting trace minerals from
poultry diets depresses productivity and tissue mineral concentrations. Patel et
al. (1997) found that removal of supplemental trace minerals and vitamins from
the diet during the period 35–42 days post hatching decreased daily weight gain
in three different broiler strains. In addition, removal of supplemental riboflavin
from the finisher diet 7 days prior to slaughter resulted in a 43% decrease in the
content of riboflavin in breast muscle. Shelton and Southern (2006) reported that
omission of a trace mineral premix from broiler diets had no effect on
productivity during the early stage of growth but had progressively deleterious
effects on productivity with increasing age of the birds. In addition, removal of
trace minerals had a negative effect on bone strength and on tissue trace mineral
concentrations. A study conducted in Turkey by Ïnal et al. (2001) with laying
hens showed that omission of a trace mineral and vitamin supplement resulted in
reduced egg production, feed intake, egg size and zinc content of eggs. These
findings are of importance to organic producers, in view of their relevance to
production efficiency and product quality.CobaltCobalt is a component of the
vitamin B12 molecule but a deficiency of cobalt has not been demonstrated in
poultry fed a diet adequate in vitamin B12. Therefore, supplementation with this
element is not normally necessary. Diets containing no ingredients of animal
origin (which contain vitamin B12) contain no vitamin B12. Therefore, poultry fed
on all-plant diets may require dietary cobalt, unless the diet is supplemented
with vitamin B12. In practice, many feed manufacturers use a cobalt-iodized salt
for all species since cobalt is needed in ruminant diets. This avoids the need to
stock separate salt types for ruminant and non-ruminant diets and the inclusion
of cobalt provides some insurance in case the poultry diet is lacking sufficient
vitamin B12.CopperCopper is required for the activity of enzymes associated
with iron metabolism, elastin and collagen formation, melanin production and
the integrity of the central nervous system. It is required with iron for normal
red blood cell formation. Copper is also required for bone formation, brain cell
and spinal cord structure, the immune response and feather development and
pigmentation. A deficiency of copper leads to poor iron mobilization, abnormal
blood formation and decreased synthesis of elastin, myelin and collagen. Leg
weakness, various types and degrees of leg crookedness and incoordination of
muscular action also result. Tibial dyschondroplasia is an example of a leg
disorder in poultry that can be caused by a copper deficiency. Poor collagen
and/or elastin formation can also lead to cardiovascular lesions and aortic
rupture, particularly in turkeys.IodineIt has been known for over 100 years that
iodine is required for the proper functioning of the thyroid gland and that an
iodine deficiency causes goitre. As a result, iodized salt is now used to prevent
this disease in humans and animals. Iodine metabolism is greatly influenced by
selenium nutrition, thus influencing basal metabolic rate and several
physiological processes. Some dietary factors are goitrogenic. Cruciferous plants
contain potential goitrogens of the thiouracil type, while brassicas and white
clover contain cyanogenetic glycosides that are goitrogenic (Underwood and
Suttle, 1999). Canola meal has resulted from the selection of rapeseed that is low
in glucosinolate, a common goitrogen. There are also goitrogenic substances in
other feeds such as carrots, linseed, cassava, sweet potatoes, lima beans, millet,
groundnuts, cottonseed and soybeans which impair hormone release from the
thyroid gland. Goitre can then occur even though the iodine level in the diet may
appear to be adequate.A high calcium level in drinking water is also known to
reduce iodine absorption and result in goitre, particularly if the dietary iodine
level is borderline. Signs of iodine deficiency include an enlargement of the
thyroid gland (which might not be noticed because of the feathers on the neck),
poor growth and reduced hatchability of the eggs. At necropsy, the thyroid is
enlarged and haemorrhagic.Most feedstuffs contain only low levels of iodine. The
exception is seaweed, which can contain 4000mg/kg
Most of the iron in the body is in the form of haemoglobin in red blood cells and
myoglobin in muscle. The remainder is in the liver, spleen and other tissues.
Haemoglobin is essential for the proper functioning of every organ and tissue of
the body. Iron has a rapid turnover rate in the chicken; therefore, it must be
provided in a highly available form in the diet on a daily basis. Iron deficiency
can result in microcytic, hypochromic anaemia in poultry. Any internal infection
such as coccidiosis can also interfere with iron absorption and lead to a
deficiency.Soil contains iron and may provide sufficient for poultry raised
outdoors on pasture. It is important, however, that the soil be free of disease
organisms and parasites.
Manganese
Manganese is essential for the synthesis of chondroitin sulfate, a mucopolysaccharide which is an important component of bone cartilage. Manganese is also
required to activate enzymes involved in the synthesis of polysaccharides and