NOTES ON THE THYROID GLAND.

New Zealand Journal of Agriculture, Volume 43, Issue 3, 21 September 1931, Page 210

NOTES ON THE THYROID GLAND.

E. M. Mason, B.Sc., Chemical Laboratory, Department of Agriculture, Wellington. A brief description of the thyroid gland, and the function of iodine in the development and maintenance of the general health of farm animals, may be of interest to Journal readers.

The. thyroid gland contains a higher percentage of iodine than any other tissue in the body. lodine absorbed by the animal passes into the thyroid, where it forms one of the chief constituents of a specific compound which exercises a profound influence on the development of the young and the maintenance of general health. A deficiency of iodine may have serious consequences, and manifests itself in very definite symptoms, the commonest of which is an enlargement of the gland itself. It may be due either to insufficient iodine in the diet of the animal, or to too great a drain on the iodine-supply. lodine helps destroy the toxins in the body, so that' unhygienic conditions of life, such as living in sunless places, rainy seasons, unprotected watersupplies, &c., may cause a serious drain in the supply. The minimum amount of iodine required for the adequate functioning of the thyroid glands of large animals is 0-03 per cent, fresh weight. A gland with less than this is generally, but not always, enlarged. Following are examples . . . r Fresh Weight. Percentage Grammes. of lodine. (1) Ten months ram lamb, Ohan, Manawatu .. . . 1-52 . 0-089 (2) Ram hogget, Westmere, Wanganui .. .. 3-95 0-013 (3) Lamb, Murchison .. .. .. .. 114-14 0-002

■ The first sample is a gland from the Manawatu district, and is typically normal. The second, . from Wanganui, although actually deficient in iodine, is only very slightly enlarged. The third is a typically bad goitre.

In extreme cases of iodine deficiency the symptoms are very pronounced ; the wool of sheep becomes coarse and hair-like, the lambs are born very weak and hairless, in many cases dead or deformed, while the animals as a whole- are listless and apathetic. (See this Journal for April, 1930, p. 226.) Fortunately, such cases are rare in New Zealand.

Since the iodine in pastures is subject to seasonal variations, and the soil iodine is not all available for use, an analysis of the thyroid gland forms the most . satisfactory indication as to the amount of iodine the animal has at its disposal. It is important to know whether any particular type of soil is more liable to be goitre-producing ; hence an attempt is being made to obtain glands from sheep reared on every type of soil, particularly from similar soils in different localities. For this reason the Department of Agriculture is asking for the co-operation of farmers in the forwarding of. glands taken from sheep and lambs which they have reared on their own properties. The difficulty in obtaining glands from abattoirs and freezing-works lies in the fact, that it is often not feasible to trace the farms from which these animals have come.

The supplementary feeding of licks in districts where the mineral content of pastures is low is coming into general practice in New Zealand, and iodine may be included where warranted. A widespread

and indiscriminate use is not to be advised, however, for as yet it has not been proved that iodine has any actual feeding-value, and an overdose is not only wasteful, but in many cases actually harmful.

How TO TAKE THE THYROID GLAND FROM SHEEP OR LAMBS.

Following is a brief description of the gland and directions for its dissection. Samples should be obtained from normal lambs, such as those killed for human consumption, as well as from abnormals — example, lambs born dead, or dying from sickness.

The thyroid is a red bilobed glandular structure growing firmly against the windpipe. To obtain a sample, when killing, cut the

throat of the sheep through or above the “ Adam’s apple ” and take out about six inches of windpipe immediately below. . Remove adhering flesh and fat until the gland is exposed. The accompanying diagram shows a normal gland in its natural relative size and position. An enlarged gland may have lobes as large as a hen’s egg. The “ isthmus ”is a very thin piece of gland joining the two lobes across the windpipe, and is somewhat difficult to remove. The gullet is on opposite side of windpipe to isthmus. A pair of fine nail-scissors is the best instrument to use for removing the gland.

The gland should be kept whole, wrapped in grease-proof paper, shut tightly in an old tobacco tin, and posted with the least possible delay. Information as to age and sex of animal, also as to whether it has had access

to iodized licks or not, should be enclosed. Samples should be addressed to the Chief Chemist, Department of Agriculture, Box 40, Wellington. .