IODINE DEFICIENCY: The Hidden Risk to Lamb Survival

Mark Facy
Jul 2
3 min read

By Mark Facy, TRAC Ruminant Productivity Consultant

Lamb survival begins long before lambing, and one of the most overlooked factors is iodine nutrition in pregnant ewes. While iodine is only required in small amounts, a deficiency during pregnancy can have significant impacts on lamb survival, particularly in high-risk environments.

Iodine is essential for the production of thyroid hormones, which regulate growth, energy metabolism and body temperature. During pregnancy, these hormones play a critical role in the development of the foetus, particularly the brain, lungs, heart and wool follicles. Lambs born to iodine-deficient ewes often struggle to regulate their body temperature, leaving them vulnerable to exposure, starvation and death shortly after birth.

Why deficiency occurs

Iodine deficiency is most common in high-rainfall regions and on sandy or light-textured soils where natural iodine levels are low. Seasonal conditions can worsen the problem, particularly during late winter and early spring when ewe iodine requirements peak but pasture iodine concentrations are often at their lowest. Heavy autumn rains followed by lush pasture growth can further increase the risk.

The last trimester of pregnancy is the critical period. Although adult sheep can draw on iodine reserves stored in their thyroid gland, the developing lamb cannot. The foetus relies entirely on the ewe's daily iodine intake during the second half of pregnancy, making consistent dietary supply essential.

The role of goitrogenic pastures

Producers should also be aware of pasture species that interfere with iodine utilization. Brassica crops such as fodder rape and turnips, along with some clovers, contain compounds known as goitrogens. These substances reduce iodine uptake by the thyroid gland and can increase the risk of Goitre and lamb mortality even when apparent iodine intake is adequate.

How iodine deficiency affects lambs

Research consistently shows that iodine deficiency in pregnant ewes can reduce lamb survival. Deficient lambs are more likely to be born weak, exhibit poor vigor, have difficulty standing and suckling, and show reduced ability to cope with cold conditions.

In severe cases, deficiency can contribute to:

Abortions and foetal resorption.
Stillbirths.
Weak or non-viable newborn lambs.
Hairless or sparsely woolled lambs.
Reduced growth and development.
Increased ewe health issues including retained placenta and reproductive problems.

Recognising the signs

The most obvious indicator of iodine deficiency is congenital goitre, an enlarged thyroid gland visible in newborn lambs. Other signs may include:

Weakness and lethargy.
Poor suckling behaviour.
Pink, bare skin and sparse wool cover.
Increased lamb losses shortly after birth.

Post-mortem examination of dead newborn lambs can help confirm a problem. Measuring thyroid weight relative to body weight is a useful diagnostic tool. Thyroid-to-bodyweight ratios above 0.4 g/kg liveweight are generally considered indicative of iodine deficiency, while severe enlargement provides stronger evidence of inadequate iodine supply during gestation.

Supplementation requires balance

While correcting a deficiency can improve lamb survival and flock performance, more is not always better. Research has shown that both iodine deficiency and excessive iodine supplementation can negatively affect lamb outcomes. High iodine intakes have been associated with reduced absorption of immunoglobulin G (IgG) from colostrum, leading to poorer immunity and lower survival rates.

For this reason, supplementation programs should be carefully planned. Iodised salt-based supplements can be useful during late pregnancy, particularly in known low-iodine areas or where a history of Goitre has been observed. Producers should also consider the contribution of feed ingredients and the presence of goitrogenic crops when assessing iodine status.

Key take-home message

Iodine deficiency is a hidden but potentially significant cause of lamb mortality. The risk is greatest in high-rainfall regions, on sandy soils, during late pregnancy and where goitrogenic pastures are grazed. Ensuring pregnant ewes receive adequate, but not excessive iodine during the final trimester can improve lamb vigour, thermoregulation and survival, ultimately increasing marking percentages and flock profitability.

If you have any questions regarding Iodine and lambing survival, please do not hesitate to talk with one of our TRAC Ruminant Experts.

Our Consultants

EXPERTS IN RUMINANT PRODUCTIVITY

Tom Thorn

0427 243 319

tomt@totalresult.com.au

Owen Rees

0429 437 823

owenr@totalresult.com.au

Mark Facy

0427 243 320

markf@totalresult.com.au