1. Iodine plays an essential role in ruminant nutrition as it is required for the production of thyroid hormones which regulate growth, metabolism and reproduction. 2. Iodine deficiency can cause goiter and other iodine deficiency disorders (IDDs) through insufficient production of thyroid hormones. Diagnosis of IDDs involves measuring iodine levels in blood, urine and milk as well as examining thyroid morphology and hormone levels. 3. Ruminants obtain iodine from plants, soil, water and feed sources. Requirements vary depending on factors like climate and production stage but average 0.11 mg/kg DM in summer and 0.54 mg/kg DM in winter for sheep.

2. Iodine in ruminants nutrition
By: M. Behroozlak Jan. 2014

3. Introduction
 The relationship between iodine nutrition and goitre only emerged
in the l9th century.
 In 1927, a putative hormone, containing 65% iodine by weight,
was isolated from thyroid tissue and called ‘thyroxine’.
 Treatment and prevention of goitre with thyroid extracts or
iodized salt became routine. Extensive ‘goitrous’ areas were
eventually discovered on every continent (Fig. 12.1), often
associated with an environmental deficiency of iodine, and these
can still cause problems in livestock.
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4. Dispersion of goitre in world
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5. Relation between iodine and goitre
 The link between geochemical iodine status and incidence of
goitre is not straightforward , being complicated by the presence
of organic, goitrogenic factors in foods.
 Subsequent discoveries of the adverse effects of iodine
deficiency on brain development, of implied effects on embryonic
viability and of selenium deprivation on iodine metabolism.
This meant that the terms ‘iodine deficiency’ and ‘goitre’ were not
synonymous, and ‘iodine deficiency disorder’ (IDD) replaced
‘goitre’ for describing the varied consequences of iodine
deprivation.
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6. 1993
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7. Minimum iodine requirements of
livestocks
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8. Function of Iodine
ORD
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9. Regulation of thyroid hormones
activity
TPO
ID
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10. Function of thyroid hormones
 Thyroid hormones have a thermoregulatory role, increasing
cellular respiration and energy production, and have widespread
effects on intermediary metabolism, growth, muscle function,
immune defence and circulation.
 These are particularly important in facilitating the change from the
fetal to the free-living stage.
 The seasonality of reproduction in ewes is related to seasonal
changes in thyroid activity.
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11. Function of thyroid hormones
 As a determinant of metabolic rate, T3 interacts with hormones
such as insulin, growth hormone and corticosterone, and
regulatory proteins of exocrine origin (leptin).
 For example, leptin production by adipose tissue is induced by
thyrotrophic hormones and controls appetite; thyroidectomy
raises plasma leptin in the ovine fetus.
In the long term, life is unsustainable without a thyroid
gland
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12. Metabolism of Iodine
 Whereas phosphorus is recycled via saliva in ruminants, iodine is
recycled via secretion into the abomasum.
 Unheated soybeans contain a heatlabile factor that can induce
goitre by impairing the intestinal recycling of iodine.
 Absorbed iodine is transported in the bloodstream loosely bound
to plasma proteins.
 Excess dietary iodine is excreted predominantly via urine as
iodide, but in lactating animals significant amounts can be
secreted in milk (Fig. 12.3).
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13. Relationship between intake and milk
secretion of iodine
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14. Activation of T4
 T4 is activated by two selenium dependent deiodinases: ID1,
which can be inhibited by propylthiouracil (PTU), and ID2,
which is relatively insensitive to PTU.
 In early lactation in cows, there is a fall in ID2 activity in the
liver and a rise in mammary tissue, accompanied by decreases
in plasma T4 and T3 concentrations.
 In newborn mammals, serum T4 and T3 concentrations rise
immediately after birth following the ingestion of colostrum
rich in T4 and T3.
This probably reflects the importance of T4 and T3
to survival in the neonate.
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15. Sources of Iodine
Soils high in iodine such as boulder clays and alluvial soils
generally produce plants richer in the element than iodine-low soils.
However, correlations between soil iodine and plant iodine are
often poor because plant species and strains differ widely in their
ability to absorb and retain soil iodine.
Proximity to the sea has a major influence on plant iodine, as
illustrated in Fig.12.4.
Forages
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16. Relation of sea & plant iodine
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17. Sources of Iodine
 Cereals and oilseed meals are poor sources of iodine.
 Fish meals are exceedingly rich in iodine; animal protein sources
are generally intermediate, but can be increased by iodine
supplementation of the source animals.
 Seaweed may contain as much 4–6 g I kg−1 DM, and its inclusion
in the rations of cows and hens greatly increases the milk and egg
iodine.
Other foodstuffs
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18. Sources of Iodine
 The iodine content of drinking water largely reflects the iodine
content of surrounding rocks and soils and correlates with
iodine concentrations in local plants of an area.
 Sea water is rich in iodine, containing > 50 μg I l−1, and
deposition of marine iodine influences drinking water iodine.
Water
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19. Sources of Iodine
 Iodine concentrations of milk are extremely variable in all species due to
the ease with which iodine crosses the mammary barrier.
 Winter milk contains over twice as much iodine as summer milk.
 Milk iodine is also influenced by stage of lactation: colostrum is two to
three times richer in iodine than main milk and concentrations decline
towards the end of lactation.
 Milk products such as dried skimmed milk, buttermilk and whey
usually contain less iodine.
Milk & milk products
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20. Sources of Goitrogens
 Plants (Brassica, white clover, cassava) can contain one or more of
about 100 different glucosinolates, along with β-glucosidases such as
myrosinase, that release HCN after structural damage to plant tissue,
during harvesting or processing.
 HCN is converted to thiocyanate (SCN) or isothiocyanate and the
process can continue during digestion, through the activity of
myrosinases.
Thyroperoxidase inhibitors
The effects of CG goitrogens are attenuated by iodine
supplementation.
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21. Sources of Goitrogens
 The synthetic goitrogen PTU can induce IDD by inhibiting ORD1
in mammals, and inhibition can therefore take place outside the
thyroid.
 Rapeseed meal (RSM) can contain 44 mmol progoitrin kg−1 DM as
its major goitrogenic component.
 Iodine supplementation does not counter the effects of ORD1
inhibitors, and short-term exposure to them may cause goitre which
is not an IDD.
Deiodinase inhibitors
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22. Iodine Requirements
The minimum ‘iodine requirement’ depends on the criterion
of adequacy:
requirements for growth are not necessarily those for
reproduction and lactation, or for maintenance of thyroid structure
and circulating levels of T4.
Furthermore, critical levels for all species are likely to vary with
environmental temperature, rate and stage of production and the
efficiency of energy utilization.
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23. Ruminants
 The mean requirements are 0.11 mg kg−1 DM in summer and 0.54
mg kg−1 DM in winter for sheep, with a similar winter value for
cattle (0.52 mg kg−1 DM).
 A significant reduction in thyroid weight in peri-natal calves (from
22.9 to 15.8 g) when the pregnant cow’s iodine intake from a grass
silage diet.
 Herbage iodine levels of 0.18– 0.27 mg kg−1 DM can sustain
normal growth in cattle, milk yield in cows and wool growth in
sheep in the summer in New Zealand.
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24. Biochemical Signs of Iodine
Deprivation
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25. Effects of iodine and selenium deficiencies,
on cGPX
25

26. Comparison
T3 > T4
T1 > T2 T4 > T3
T2 > T1
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27. Responses of cashmere goats to oral doses
of PTU (a goitrin)
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28. Clinical Manifestations of Thyroid
Dysfunction
 Goitre Thyroid enlargement (in newborn animal)
 Impaired fertility Infertility, sterility, poor conception
rate, decline in libido and deteriration in semen
quality
 Impaired embryo and fetal development
 Disorders of the integument
 Post-natal mortality and growth retardation
 Low milk yield
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29. Goiter in lamb
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30. Diagnosis of Iodine Deficiency
Disorders
 Thyroid morphology, histology and composition (Thyroid weight)
 Iodine in the bloodstream (Serum iodine, PBI and T4 in bloodstream)
 T4 assays
 T3 assays
 Iodine in urine and milk:
Where thyroid dysfunction is induced by CG, urine iodine will
probably be deceptively high and milk iodine deceptively low.
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31. T3 & T4 state in the first week after
birth
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32. The best diagnosis method
 Simple microplate ELISA assays for TSH are now widely used
to predict goitre prevalence in infants and should be adopted for
livestock.
 Adaptive increases in ORD activity clearly indicate imminent
thyroid dysfunction and have potential diagnostic value in
livestock.
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33. Iodine Toxicity
 Exposure to excess iodine paradoxically results in
hypothyroidism because of feedback inhibition of T3 synthesis.
pig & poultry > sheep > cow > horse
Tolerance
300-400 mg/kg DM 50 mg/kg DM
25-50 mg/kg DM
5 mg/kg DM
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