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Iodine deficiency in sheep
Iodine is the building block for thyroid hormones, which regulate how quickly the body functions. In pregnant ewe, it is essential for the development of the lamb. When the ration lacks it, the lamb's thyroid gland enlarges to compensate: t...
What is it?
Iodine is the building block for thyroid hormones, which regulate how quickly the body functions. In pregnant ewe, it is essential for the development of the lamb.
When the ration lacks it, the lamb's thyroid gland enlarges to compensate: this is goiter, this clearly visible swelling at the base of the neck that breeders describe as a big neck.
The adult sheep often shows almost nothing. It is the lamb that pays: stillborns, lambs born weak, without wool or with thinning wool, unable to get up and suckle, which die within the first hours.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
In lambs, at birth: firm, symmetrical swelling at the base of the neck, on each side of the trachea, sometimes the size of a fist.
Lambs who are stillborn or die within the first few hours, often well formed but unable to stand and suckle.
Wool absent, very short or sparse on part of the body; skin that appears bare in places.
Soft, cold lambs, without sucking reflex, which do not seek the udder.
Difficulty breathing when the goiter is large and compresses the trachea.
In those who survive: slowed growth, stunted animals, sensitive to cold and disease.
In sheep: few visible signs, but a disappointing breeding season, returns to heat, reduced fertility, late abortions and small litters.
A strong indicator: several consecutive lambings go wrong in the same flock, without any infectious disease being revealed.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
Soils and fodder naturally poor in iodine, often far from coastal areas or on leached land.
Consumption of so-called goitrogenic foods, which prevent the gland from using available iodine: plants from the cabbage and cruciferous family, rapeseed, turnips, certain oilcakes, as well as large quantities of raw soya.
Needs greatly increased at the end of gestation, the period when the lamb develops most quickly: a correct ration for the rest of the year may become insufficient at this precise moment.
Absence of iodized mineral supplement, or supplement not consumed by animals.
An excessive intake of iodine is also harmful: correction is therefore never done by dead reckoning.
Ewe at the end of gestation, a period of all needs.
Ration based on fodder produced locally in an area poor in iodine.
Significant use of cruciferous vegetables, forage cabbages, rapeseed or turnips in the winter diet.
Absence of mineral supplement intended for sheep, or block that the animals do not consume.
Herds led on a range, difficult to supplement regularly.
Association with other deficiencies, notably selenium, which aggravate the weakness of lambs at birth.
Lambing in cold periods: a deficient lamb resists the cold even less well.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The most telling sign is goiter in lambs: the veterinarian palpates the base of the neck of newborns, including stillborns, and compares with lambs from the same farm.
The autopsy of a stillborn lamb is particularly useful: the thyroid gland is weighed and compared to the body weight, which gives a clear answer.
Blood tests on the ewes and dosages on the fodder help complete the picture and determine whether the problem comes from the soil, the ration or both.
The veterinarian rules out other causes of mortality in lambs at birth, which are numerous and easily confused: abortive diseases, selenium deficiency, hypothermia, difficult birthing, poorly nourished ewes. Some are contagious and require very different behavior.
A review of the end-of-gestation ration, carried out with the veterinarian, always completes the analysis: this is often where the key lies.
Treatment
The correction is based on an appropriate iodine intake, prescribed by the veterinarian, in the form of a specific sheep mineral supplement, blocks or preparations administered to ewes during pregnancy.
Neither the quantity nor the duration can be improvised: too much iodine is as harmful as a lack, and also causes problems in the lambs. This is one of the rare deficiencies where overcorrection is a real risk.
Foods that block iodine utilization should be reduced or eliminated late in gestation; their maintenance cancels the effect of the supplementation.
A lamb born with a large goiter requires immediate newborn care: drying it, warming it, making sure it receives colostrum quickly. The goiter itself slowly regresses in those who survive.
No treatment subsequently makes up for the development missed during gestation: everything happens before birth, which makes this deficiency a prevention problem above all.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Ensure a ration adequately supplied with iodine, particularly during the last six to eight weeks of gestation, with a mineral and trace element supplement formulated for sheep.
Check that the supplement is actually consumed: a full tank at the end of the season indicates that the supplement has not taken place.
Limit cruciferous vegetables, cabbages, rapeseed and turnips in the diet of pregnant ewes, or compensate for their use after veterinary advice.
Have forages analyzed on farms that encounter repeated problems with weak lambs.
Systematically palpate the neck of stillborn lambs: it is a simple reflex which allows you to spot the problem in the first season rather than after three.
Do not increase iodine intake on your own initiative: the correction is made on prescription.
Monitor selenium and the body condition of the ewes at the same time, because weaknesses in lambs at birth are often of multiple origins.
Possible complications
Significant mortality of lambs in the hours following birth, often the heaviest loss of the season.
Weak surviving lambs, sensitive to cold and respiratory diseases, which remain late all their lives.
Compression of the trachea by a large goiter, with difficulty in breathing.
Retained placenta and poor recovery in ewes.
Fertility decreased over the following season if nothing is corrected.
Discouragement of the breeder, who wrongly attributes the losses to cold or bad luck when a simple dietary correction would have sufficed.
When to see a veterinarian
Lambs are born with a swelling at the base of the neck.
Several lambs are born dead or die in the first hours without explanation.
Lambs are born without wool or with very sparse wool.
Lambs are limp, do not get up and do not look for the breast: consult without delay, the window to save them is very short.
The lambing season is going poorly even though the ewes appeared to be in good condition.
Your sheep get plenty of cabbage, rapeseed or turnips during the winter.
Prognosis
Lambs born with a marked goiter have a guarded prognosis: many die within the first few hours, and survivors lag behind.
In ewes, the correction of the ration gives excellent results from the following season: it is a deficiency which is easily resolved when it is identified.
The prognosis of the flock therefore depends on the speed with which the problem is recognized, hence the interest in examining stillborn lambs rather than evacuating them without looking at them.
Frequently asked questions
My lambs are born with big necks, is this contagious?
No. Goiter is not a contagious disease: it reflects a lack of iodine during the mother's gestation, or the presence of foods which block its use. The problem is solved in the sheep's ration, not by treating the lambs.
Can I just give more iodine to be safe?
No, and this is important: excess iodine also causes problems in lambs and can harm the ewe. This is one of the deficiencies where we never correct the dead reckoning. Ask the veterinarian for the form and quantity suitable for your ration.
Are cabbages and rapeseed really to blame?
They do not create the deficiency on their own, but they prevent the body from properly using the available iodine. On an already fair ration, a large distribution at the end of gestation is enough to tip the herd over.
My sheep are doing well, how can they lack iodine?
Because the adult ewe tolerates an insufficient intake for a long time without showing anything, while the developing lamb has an immediate need. This is why the problem almost always reveals itself at birth, in lambs, and not in mothers.
References
FAO — Organisation des Nations unies pour l'alimentation et l'agriculture
ANSES — Agence nationale de sécurité sanitaire (France)
Content reviewed by the TunisieVet editorial team · Updated 11 August 2026
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