Congenital Goiter in Lambs: Thyroid Enlargement at Birth

Congenital goiter in lambs is an abnormal enlargement of the thyroid gland that is present at birth or noticed shortly afterward. The thyroid sits in the lower neck and helps regulate growth, metabolism, temperature control, and normal fetal development. When the gland cannot make enough thyroid hormone during pregnancy, it may enlarge in response to increased thyroid-stimulating hormone.

In sheep, congenital goiter is most often tied to iodine deficiency in the ewe during gestation, especially in areas with iodine-poor soil or when the flock's mineral program is not well balanced. Goitrogenic feeds and inherited defects in thyroid hormone production can also play a role. Lambs may be born weak, slow to nurse, poorly wooled, or with a clearly enlarged throat area.

This condition can range from mild to life-threatening. A small thyroid enlargement may improve once the flock's iodine intake is corrected, but severe cases can be associated with stillbirth, death soon after birth, or long-term poor growth. Because several different newborn problems can look similar, your vet should help confirm the cause before any treatment plan is chosen.

The most common cause is iodine deficiency during pregnancy. If a ewe does not get enough iodine, the developing fetus may not produce adequate thyroid hormone. In response, the fetal thyroid enlarges, creating the goiter seen at birth. This is more likely in regions with iodine-deficient soils or when sheep are not receiving a properly formulated sheep mineral.

Another cause is exposure to goitrogenic feeds or plants, which interfere with normal iodine use by the thyroid. Brassica plants are a classic example. Even when iodine intake is borderline normal, goitrogens can create a functional deficiency. In practice, this means your vet may look not only at the mineral tag, but also at hay, pasture, supplements, and any unusual feed ingredients used during late gestation.

Less commonly, congenital goiter is related to inherited defects in thyroid hormone synthesis, sometimes called familial dyshormonogenetic goiter. In these cases, the gland enlarges because it cannot make hormone normally even if iodine is present. These lambs may be weak, poorly wooled, and prone to early death. Because several flock-level nutrition and genetics issues can overlap, a careful history is important before deciding what changed and what should be corrected.

Diagnosis starts with a physical exam and a flock history. Your vet will look at the size and location of the neck swelling, the lamb's strength, nursing ability, body temperature, and wool coat. They will also ask about the ewe ration, mineral access, pasture type, stored feeds, and whether other lambs were stillborn, weak, or born with similar swelling.

In many field cases, diagnosis is based on the combination of a newborn lamb with ventral neck enlargement and evidence of a maternal iodine problem. Depending on the situation, your vet may recommend bloodwork to assess thyroid hormone status, necropsy of a deceased lamb, or laboratory testing of feed and minerals. These steps can help separate congenital goiter from abscesses, congenital cysts, edema, or other causes of throat swelling.

If several lambs are affected, the workup often expands to the whole flock. That may include reviewing the mineral label, checking whether sheep had consistent access to iodized mineral, and testing feed for nutrient balance or goitrogen exposure. Confirming the cause matters because correcting the ewe flock's nutrition is usually the key step for preventing the next round of cases.

Prevention focuses on the ewe flock, especially during breeding and gestation. Sheep should have reliable access to a sheep-formulated mineral that includes iodine in appropriate amounts. This matters most in areas with iodine-poor soils, in flocks fed stored forages for long periods, or when home-mixed rations are used. Your vet or flock nutritionist can help review the full ration instead of relying on one product label alone.

It also helps to reduce exposure to goitrogenic feeds and plants during pregnancy when possible. Brassica-type plants can interfere with iodine use, so they should be considered as part of the whole diet picture. Sudden feed changes late in gestation are another good reason to pause and review the ration carefully.

If your flock has had affected lambs before, ask your vet about a prevention plan well before the next lambing season. That may include feed analysis, mineral program review, and tracking which ewe lines produced affected lambs. Prevention is usually much more effective than trying to reverse severe disease after a lamb is born.