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Volume 64, 1935
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An Iodine Survey of New Zealand Live-stock.

Part II.
The Sheep of the Wairarapa District.

[Received by Editor, 23rd May, 1933: issued separately. May. 1934.]

Symptoms suggesting acute iodine deficiency in the sheep of the Wanaka district (South Island) have been reported and described by Hopkirk, Dayus, Simpson, and Grimmett (1930). There the loss of lambs was serious, and the cure, by means of iodised licks, complete and impressive. A research was therefore inaugurated by the Department of Agriculture to find whether this deficiency was present in milder form in other parts of the country, and if so, the conditions under which it occurred and the best methods of treatment. An account of the investigation of Otago and Southland has already been published as Part I of this series by E. M. Mason (1933). The following is an account of the progress that has been made in the North Island.

The presence or absence of iodine deficiency has been ascertained from the analysis of the thyroid glands, and the results have been correlated with data referring to the conditions under which the sheep were reared. The glands were obtained from the freezing works of the district, through co-operation with the Government Veterinarian, who also supplied details of age, sex, supplementary feeding, type of soil, and morphology of the district. Each sample consisted of the thyroids of about eight animals chosen as fair representatives of the flock.

Analysis: The glands were dissected free from fatty tissue, weighed, estimated for moisture, and analysed for total iodine by the modified method of Fellenberg (Leitch and Henderson, 1926–30) adapted slightly for thyroids, but the same in all details as used by E. M. Mason (1933).

An outline of the procedure is as follows:—

The dried gland is digested in potassium hydroxide (Merck extra pure) and an aliquot of the solution evaporated to dryness in a nickel crucible. The residue is ashed at a low temperature, cooled, moistened with distilled water, dried, and ashed again, the process being repeated three or four times till the ash is greyish-white. It is then moistened and evaporated till a skin appears on the surface. It is extracted four times, each with 3 cc. of alcohol (distilled from sodium carbonate) and filtered into a small nickel crucible, evaporated

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to dryness, and drawn over a burner for five seconds to destroy traces of organic matter. The residue is dissolved in distilled water and an aliquot taken. This solution, containing the iodine in the form of potassium iodide, is made just acid, and the iodide oxidised to iodate with freshly prepared bromine water. The iodine is then liberated with excess potassium iodide solution (freshly prepared), starch is added, and the blue colouration is removed with N/500 thiosulphate, using a micro burette, and arranging quantities to obtain a titre of about 1 cc. The end point is determined by making a series of titrations varying by 0.02 cc. and accepting the figure between that value at which the colouration just reappears on standing, and the nearest one at which it disappears.

The condition of the thyroid gland was studied in relation to the factors of (1) age, (2) sex, (3) soil type, (4) iodine feeding; the first two being constitutional, the last two environmental.

(1) The condition of the thyroid gland in relation to the age of the sheep:

Samples from animals, varying in age from three months to six years, showed that age considerably affected the glands. The following are the results:—

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Description. Fresh weight of gland in grams. % Moisture. % Iodine on fresh weight.
Sheep (1½–6 years old). Average of 5 samples 3.95 70.0 0.141
Lambs (3–6 months old). Average of 86 samples 2.25 73.3 0.073

The number of sheep thyroids was not sufficient to allow the matter to be treated statistically, but from the figures available it appears that both the weight of the gland and the per cent. iodine are considerably greater in the older sheep. This result is, at least, sufficiently definite to show that where figures are being studied for any other factor, sheep results must be separated from the results of younger animals, and, in the rest of the work only lambs' thyroids are considered.

(2) The condition of the thyroid gland in relation to the sex of the sheep:

The effect of sex was also investigated, and it was found that the glands of male lambs did not differ in any way from those of

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female lambs. The following are the results of 43 samples of glands from male lambs with the corresponding samples from female lambs:

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Description. Fresh weight of gland in grams. % Moisture. % Iodine on fresh weight.
Male lambs. Average of 43 samples 2.28 73.4 0.072
Female lambs. Average of 43 samples 2.21 73.2 0.073

These results are represented graphically in the following cumulative distribution diagrams, which are a modification of the ogive (Fisher 1927) in which the scale is adapted so that a normal distribution results in a straight line. A complete explanation of this type of graph is given by Dufton (1930). The points are obtained by taking the percentage of the samples as ordinates, which lie on or below the different values shown as mantissae. The more nearly normal the distribution is, the more nearly straight will be the curve drawn through these points; the more upright the curve, the closer the limits of variation, and if on one diagram two or more curves are drawn, then the nearer they lie, the more nearly identical are the results they represent. If they lie distinct from one another there is a significant difference in the results.

The value on the curve, corresponding to the 50 per cent. mark is the median, half the samples having more and half less than this value. If the distribution is normal, then this value will also be the mean or average. It will be seen from the table above and in Diag. I-III that in this case the mean and the median agree very closely.

For the results embodied in this paper the chief advantage of this type of presentation over the more familiar histogram lies in the greater facility with which several sets of figures can be represented on one diagram.

No marked difference can be detected in per cent. iodine, wet weight, or per cent. moisture, either from the figures above or from the distribution diagrams. It was concluded, therefore, that there was no variation in lambs' thyroids in relation to sex. Fenger (1913) studied cattle and reported finding the per cent. iodine in the female slightly higher than in the male. Seventeen male thyroids had an average of 0.21 per cent. on the dry gland; twenty-three female thyroids had an average of 0.25 per cent. McCarrison and Madhava (1932) found that in rats the weights of the male thyroid glands were greater than the weights of female glands, but considered this to be due to the increased body weight of the male, and that for the same body weight there is no significant difference in weight between the glands of male and female. In the present case it is animals of approximately the same body weight which are being studied, because the lambs are those selected by fat stock buyers for killing purposes. The results obtained showing no significant difference in weight between male and female glands is therefore in agreement

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with that of McCarrison and Madhava. For the remainder of the work the plan was adopted of combining the data obtained from both sexes.

(3) The condition of the thyroid gland in relation to soil type:

The Wairarapa district is an area approximately 100 miles long and 50 miles broad. It is bounded on the west and the south-east by greywacke mountains. To the east the hills are mainly younger marine sediments—papa and mudstone (Miocene and Cretaceous), with strips of Pliocene limestone. The broad central area, comprising the river bed of the Ruamahunga River and its tributaries, consists of alluvial plains of greywacke gravel, subject to flooding, whilst on the east coast, associated with the Wareama River, there is a smaller alluvial plain. The rainfall is 40–60 inches, with 120–180 rain days.

For the purposes of this study, the district has been divided into four: (a) limestone, (b) greywacke, (c) papa, (d) alluvium, all of which, with the possible exception of the papa, are fairly pure representatives of their type. Analyses of the glands obtained from these types are given below in four groups with an extra division for swamps. The number of lobes, of which there are two to each gland, is given rather than the number of glands, as some mutilated lobes were rejected, leaving an odd number in some of the samples.

Table I.

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Limestone (21 samples).
Sample No. Fresh weight, grams. Dry weight, grams. % Iodine, fresh. % Iodine, dry. Total Iodine, grams. % Moisture. No. of lobes. Locality.
7 1.693 0.475 0.134 0.467 0.00227 72.0 18 Te Ore Ore
8 1.530 0.417 0.117 0.429 0.00179 72.7 20 "
9 1.991 0.592 0.106 0.357 0.00211 70.2 20 Pahiatua
10 1.968 0.489 0.093 0.376 0.00184 75.1 16 "
11 1.999 0.540 0.092 0.340 0.00183 73.0 18 Gladstone
14 1.953 0.584 0.097 0.324 0.00189 70.1 28 Rangitumu
23 1.641 0.495 0.033 0.109 0.00054 69.8 18 Longbush
27 1.622 0.511 0.131 0.416 0.00213 68.5 12 "
29 2.327 0.626 0.091 0.338 0.00211 73.1 16 Konini
30 2.160 0.618 0.092 0.321 0.00198 71.4 16 "
32 1.374 0.418 0.109 0.359 0.00150 69.6 20 Pahiatua
34 1.990 0.588 0.091 0.309 0.00182 70.5 24 "
52 1.767 0.496 0.125 0.445 0.00221 71.9 18 Mauriceville
53 1.866 0.504 0.120 0.446 0.00225 73.0 16 "
56 2.452 0.702 0.097 0.337 0.00237 71.4 20 Gladstone
57 1.746 0.461 0.097 0.367 0.00169 73.6 14 "
58 1.433 0.374 0.077 0.297 0.00111 74.0 16 "
59 3.355 0.932 0.064 0.229 0.00214 72.5 20 Longbush
60 1.505 0.398 0.074 0.279 0.00111 73.6 16 Gladstone
74 1.809 0.478 0.105 0.398 0.00190 73.6 12 Pahiatua
78 2.010 0.560 0.109 0.393 0.00220 72.2 20 "
Aver.: 1.91 0.537 0.094 0.349 0.00185 72.0 18
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Table II.

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Greywacke (13 samples).
Sample No. Fresh weight, grams. Dry weight, grams. % Iodine, fresh. % Iodine, dry. Total Iodine, grams. % Moisture. No. of lobes. Locality.
3 1.640 0.480 0.082 0.280 0.00134 70.7 14 Martinborough
4 1.814 0.518 0.083 0.292 0.00151 71.4 12 "
21 1.840 0.501 0.089 0.327 0.00164 72.8 6 Mt. Bruce
25 2.074 0.589 0.091 0.323 0.00190 71.6 24 "
33 1.960 0.576 0.125 0.427 0.00246 70.6 16 Martinborough
35 1.832 0.538 0.108 0.367 0.00197 70.6 18 "
63 2.036 0.520 0.089 0.350 0.00182 74.5 10 Carrington
65 2.117 0.540 0.077 0.303 0.00164 74.5 8 "
70 2.455 0.633 0.056 0.215 0.00136 74.2 18 "
75 2.227 0.579 0.068 0.261 0.00151 74.0 16 Upper Hutt
83 1.984 0.538 0.073 0.270 0.00145 72.9 14 "
85 2.526 0.562 0.056 0.253 0.00142 77.8 14 Stronvar
87 2.095 0.420 0.062 0.311 0.00130 80.0 6 "
Aver.: 2.05 0.540 0.082 0.306 0.00164 73.5 14

Table III.

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Papa (21 samples).
Sample No. Fresh weight, grams. Dry weight, grams. % Iodine, fresh. % Iodine, dry. Total Iodine, grams. % Moisture. No. of lobes. Locality.
5 1.663 0.475 0.126 0.442 0.00210 71.4 16 Martinborough
6 2.035 0.596 0.147 0.501 0.00299 70.7 14 "
16 2.537 0.746 0.118 0.401 0.00299 70.6 20 Pongaroa
17 2.013 0.590 0.035 0.121 0.00071 70.7 19 "
22 2.066 0.560 0.113 0.416 0.00233 72.9 18 Bideford
28 2.140 0.602 0.074 0.262 0.00157 71.8 20 Pahiatua
31 2.035 0.545 0.075 0.279 0.00152 73.3 20 Tinui
36 2.171 0.613 0.077 0.266 0.00163 71.8 20 "
37 1.874 0.532 0.078 0.274 0.00146 71.6 18 Pahiatua
38 2.829 0.710 0.044 0.173 0.00123 74.9 22 Bideford
39 2.158 0.552 0.050 0.195 0.00108 74.4 18 Martinborough
42 2.522 0.643 0.053 0.209 0.00134 74.5 20 "
43 2.959 0.730 0.036 0.145 0.00106 75.4 16 Bideford
69 2.113 0.560 0.070 0.264 0.00148 73.5 14 Pongaroa
72 2.374 0.595 0.071 0.284 0.00169 74.9 12 "
100 1.795 0.472 0.081 0.307 0.00145 73.7 14 Wangaehu
101 1.976 0.522 0.101 0.383 0.00200 73.6 11 "
102 2.355 0.541 0.037 0.163 0.00088 77.0 12 Martinborough
103 2.471 0.629 0.040 0.158 0.00099 74.5 20 "
104 3.027 0.838 0.049 0.177 0.00148 72.3 22 Pahiatua
105 2.602 0.706 0.041 0.189 0.00133 73.3 20 "
Aver.: 2.27 0.608 0.072 0.267 0.00158 73.2 17
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Table IV.
Alluvium (32 samples).
Sample No. Fresh weight, grams. Dry weight, grams. % Iodine, fresh. % Iodine, dry. Total Iodine, grams. % Moisture. No. of Iobes. Locality.
40 2.132 0.572 0.061 0.228 0.00130 73.2 25 Kaiwaiwai
41 2.509 0.682 0.064 0.236 0.00161 72.8 16 "
46 2.728 0.729 0.040 0.151 0.00110 73.3 10 Pigeon Bush
47 2.705 0.653 0.023 0.097 0.00063 79.6 12 "
48 2.125 0.556 0.060 0.228 0.00127 73.9 18 Featherston
49 2.132 0.564 0.054 0.204 0.00115 73.6 22 "
51 2.659 0.678 0.044 0.174 0.00118 74.5 24 Kahutara
55 3.703 0.843 0.022 0.095 0.00080 77.2 18 Pirinoa
64 2.961 0.785 0.035 0.131 0.00103 73.5 16 East Taratahi
67 2.776 0.706 0.037 0.147 0.00104 74.6 22 Homewood
68 2.751 0.810 0.046 0.157 0.00127 70.5 18 "
71 2.751 0.717 0.045 0.174 0.00125 74.0 18 Opaki
73 3.401 0.911 0.037 0.139 0.00127 73.2 24 "
76 2.904 0.714 0.044 0.178 0.00127 75.4 16 Upper Plain
77 2.713 0.707 0.060 0.231 0.00163 73.9 14 Pigeon Bush
79 1.954 0.508 0.077 0.297 0.00151 74.0 14 Martinborough
80 2.349 0.643 0.086 0.313 0.00201 72.6 18 Pigeon Bush
81 2.148 0.582 0.076 0.279 0.00163 72.9 16 Martinborough
82 2.088 0.522 0.051 0.203 0.00106 75.0 20 Upper Plain
84 2.525 0.671 0.080 0.302 0.00203 73.4 24 Opaki
86 2.575 0.659 0.050 0.196 0.00126 74.4 18 Langdale
88 2.815 0.703 0.049 0.198 0.00139 75.1 14 "
89 2.623 0.691 0.055 0.208 0.00144 73.7 20 Opaki
90 2.985 0.739 0.033 0.134 0.00099 75.2 18 Pirinoa
91 2.250 0.569 0.053 0.209 0.00119 74.7 16 Martinborough
92 3.112 0.757 0.032 0.130 0.00099 75.7 18 Pirinoa
93 2.547 0.572 0.027 0.120 0.00069 77.6 16 "
94 3.117 0.727 0.017 0.073 0.00053 76.7 18 "
95 1.893 0.458 0.049 0.205 0.00094 75.8 12 Martinborough
98 2.040 0.498 0.047 0.191 0.00095 75.7 12 Manaia
99 2.400 0.617 0.034 0.130 0.00080 74.2 20 "
109 3.468 0.849 0.023 0.093 0.00079 75.5 24 Pirinoa
Avei.: 2.62 0.668 0.047 0.183 0.00117 74.5 18

Table V.

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Swamp (4 samples).
Sample No. Fresh weight, grams. Dry weight, grams. % Iodine, fresh. % Iodine, dry. Total Iodine, grams. % Moisture. No. of lobes. Locality.
44 1.799 0.528 0.111 0.414 0.00219 70.6 18 Kahutara
45 2.021 0.599 0.145 0.489 0.00293 70.3 14 "
96 1.787 0.480 0.102 0.380 0.00182 73.3 16 Opaki
97 1.817 0.497 0.111 0.407 0.00202 72.7 14 "
Aver.: 1.856 0.526 0.117 0.422 0.00224 71.7 16
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Diagram I.
% Iodine

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Cumulative distribution diagram of the % iodine in glands of male and female lambs.

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Diagram II.
Fresh Weight
(Grams)

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Cumulative distribution diagram of the weight of glands in male and female lambs.

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Diagram II.
% Moisture

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Cumulative distribution diagram of % moisture in glands of male and female lambs.

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Diagram IV.
Fresh Weight
(Grams)

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Cumulative distribution diagram showing relation of fresh weight of glands to soil types.

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Diagram V.
% Iodine
(Fresh)

Picture icon

Cumulative distribution diagram showing relation of % iodine of glands to soil types.

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Diagram VI.
% Moisture

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Cumulative distribution diagram showing relation of % moisture to soil types.

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Diagram VII.
Total Iodine
(Grams)

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Cumulative distribution diagram showing relation of total iodine in glands to soild types.

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(a) Limestone:

Many instances of goitre endemic on limestone areas are cited by Hercus, Benson, and Carter (1925) in their study of the relationship between goitre and geological type. In England, Lebour (1881) concluded that goitre was absent on Jurassic limestone, but was endemic on the older Carboniferous limestone. McCarrison showed that goitre was associated with limestone areas in Northern India. Clark and Pierce (1914) found goitre endemic on Silurian limestone in the Virginias. In Switzerland, however, the lowest incidence of goitre is associated with marine Mesozoic rocks, chiefly limestone, marl, and claystone.

This great disparity between the relationship of goitre to limestone is not surprising, for there are, besides iodine deficiency, other goitrogenic agents which may or may not be operating in the localities studied. Again, the iodine content of different limestones must vary according to factors such as the amount of organic matter originally deposited, to the time and severity of leaching, to the presence or absence of clays and other colloids which would tend to prevent the leaching, to vegetable and animal life, and to the cropping. Further, lime itself tends to cause thyroid enlargement, especially in conjunction with vitamin and iodine deficiency (McCarrison and Madhava, 1932). No conclusions can be made, therefore, concerning the goitrogenic effect of limestone formations generally, although conditions for particular deposits appear to be constant.

The formation at present being studied is a comparatively recent marine deposit, rich in organic remains. From the preceding figures and diagrams it is seen that the glands from this area have the greatest percentage and total iodine, and least weight and percentage moisture of any of the groups, excluding the swamp samples. There is only one case of a sample of average weight greater than three grams, and only one of low iodine content. The limestone areas of this district may be said, therefore, to be free from goitre.

(b) Greywacke:

Greywacke deposits, in their relation to goitre incidence, have not been as fully reported on as limestone. In the present case the glands from the greywacke areas rank next to those from the limestone in point of iodine content and freedom from enlargement; no suggestion of iodine deficiency was obtained from this area.

(c) Papa:

Concerning formations of this nature, Hercus, Benson, and Carter (1925) quote conflicting reports. Lebour (1881) considered that goitre was absent from Jurassic claystone and rare on Cretaceous claystone. McCarrison found Cretaceous and Post Tertiary deposits comparatively free from goitre. Clark and Pierce (1914) describe the presence of claystones in the non-goitrous areas of Virginia.

It may be that the nature of the deposit varies in the preceding cases; it certainly does in the case of the Wairarapa deposits. Some parts are dark grey Cretaceous mudstone and some are light-coloured

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miocene papa; some parts are fossiliferous and others are not. Attempts at further dividing this type were not successful, so more samples are being obtained which may make the matter clearer.

Although lacking uniformity, samples from this area, when compared with those from the limestone and greywacke areas, show a definitely lower iódine content and an increased weight. There is, however, no instance of gross enlargement or acute iodine deficiency in any of these samples.

(d) Alluvium:

High incidence of goitre associated with alluvial soils in New Zealand has been demonstrated by both Hercus, Benson, and Carter (1925) and Shore and Andrew (1929). The same phenomenon has been observed in Switzerland and in North America, in the region of the St. Lawrence and the Great Lakes (Orr and Leitch, 1929).

Although the application of fertilizers, which have been shown by Hercus and others (1931) to increase the iodine content of the pastures, has been more extensive on the alluvial plains than on limestone, greywacke, and papa hills, yet the thyroid glands from the plains are low in iodine and high in weight. In some cases the percentage iodine is less than 0.03 (fresh), the level below which normal functioning of the gland is considered by Marine and Lenhart (1901) to be impossible.

The samples with the smallest iodine content and the greatest weight come from the lower part of the valley near the mouth of the Ruamahunga River. Shore and Andrew (1929) showed that the iodine content of the soil exhibited a marked decrease on proceeding down the valley towards the sea. Apparently in both these river basins, which are subject to flooding, the soil has been more thoroughly leached of iodine in the lower part of the valley.

The samples in the alluvial group show a lower iodine content and a higher weight and moisture percentage than those in any other group. Not even the glands of lowest iodine content, however, show any gross enlargement.

(e) Swamp:

In swamps there is a large accumulation of organic matter, and this type of soil has been shown by Shore and Andrew (1929) to be particularly high in iodine. The glands from swampy areas are therefore considered separately from those of the alluvial plains on which these swamps occur. The glands show a higher iodine content and a lower weight than those of any of the preceding groups.

Relationships among the Changes in the Gland:

Taking the average figures of the groups considered, it is seen that a decrease in the total and relative amounts of iodine in the gland is accompanied by an increase in the fresh weight, the dry weight, and the percentage moisture.

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Table VI.

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Fresh weight, grams. Dry weight, grams. % Iodine, fresh. % Iodine, dry. Total Iodine, grams. % Moisture.
Swamp 1.86 0.526 0.117 0.422 0.00224 71.7
Limestone 1.91 0.537 0.094 0.349 0.00185 72.0
Greywacke 2.05 0.540 0.082 0.306 0.00164 73.5
Papa 2.27 0.608 0.072 0.267 0.00158 73.2
Alluvium 2.62 0.668 0.047 0.183 0.00117 74.5

(4) The condition of the thyroid gland in relation to iodine feeding:

The Wairarapa Training Farm, because of its position on the alluvial plains, was chosen for an experiment to find what changes in the gland and possible benefits to the animal would result from feeding iodised licks. One batch (No. 1) received no lick, one (No. 2) received lick containing 2 oz. potassium iodide per ton of common salt, one (No. 3) received lick containing 60 oz. potassium iodide per ton. The lick was fed at the rate of 8 oz. per animal per month, from the middle of October till the middle of December, when the animals were killed.

The averaged results are given below:—

Table VII.

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Batch No. Wet weight, gram. Dry weight, grams. Body weight, lbs. r* % Iodine, fresh. % Iodine, dry. Total Iodine, grams. % Moisture. No of lobes.
1 1.76 0.478 36.4 10.65 0.051 0.189 0.00092 72.2 16
2 1.70 0.465 35.0 10.70 0.060 0.210 0.00107 73.1 22
3 1.80 0.558 35.2 11.26 0.105 0.351 0.00197 70.2 4

This property is manured rather more heavily than most, and the control glands are, unfortunately for the experiment, not particularly poor in iodine, nor do they show any tendency to enlargement. The effects of iodine feeding are not as marked, therefore, as could have been expected had the controls shown the tendency to low iodine content and enlarged gland, which characterises most of the glands taken from the plains.

[Footnote] * “r” denotes thyroid weight × 10,000/body weight in grams.

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No regular change has occurred in the weight or the moisture percentage of the glands, nor in the body weights of the animals, and although the ratio (r) of the thyroid weight to the body weight shows a regular increase, it is small, and its significance doubtful. The absolute and relative amounts of iodine in the gland have increased in accordance with the dose administered.

Summary:

(1) Analyses have been made of a large number of thyroid glands of lambs and sheep from the Wairarapa district in the North Island of New Zealand.

(2) The iodine estimations have been made by the method of Leitch and Henderson (1926).

(3) The glands of older sheep have been found to differ materially from those of lambs, and have been omitted from subsequent considerations.

(4) No difference could be detected between the glands of male and female lambs.

(5) The Wairarapa district has been considered from the point of view of the four main geological types there—limestone, grey-wacke, papa, and alluvium.

(6) The average iodine content.of the thyroid glands from these types was found to be:—

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% Iodine on fresh weight.
Limestone 0.94
Greywacke 0.82
Papa 0.72
Alluvium 0.47

(7) A decrease in the relative and absolute amounts of iodine in the gland is accompanied by an increase in the fresh weight, the dry weight, and the percentage moisture.

(8) In no case was there an occurrence of gross enlargement of the gland.

(9) Feeding lambs with iodised licks for two months before killing had the effect of increasing the iodine content of the thyroid glands, but no other changes or benefits were observed.

(10) The Wairarapa district is not an area of serious iodine deficiency.

The author wishes to record his indebtedness to Mr B. C. Aston, Chief Chemist, Department of Agriculture, for help and criticism; also to Mr W. C. Barry, District Superintendent, and Mr T. H. Hankin, Veterinarian, who arranged the sending of samples.

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References.

Fenger, 1913, J.B.C. 14, 397.

Dufton, 1930. Phil. Mag., X, 366.

Fisher, 1930. Statistical Methods for Research Workers. Oliver and Boyd. Third edition.

Hercus, Benson and Carter, 1925. Journ. of Hygiene, XXIV, 3–4, 322, from whom also is quoted:—

Lebour, 1881. Proc. North Counties Branch Brit. Med. Assoc.

Clark and Pierce, 1914. U.S. Public Health Service P.H. Reports, XXIX, 16.

McCarrison, 1906. Lancet, I, 1110; II, 1370.

—— 1913. Lancet, I, 147.

—— 1924. B.M.J., 989.

Hercus, Aitken, Thomson and Cox, 1931. Journ. of Hygiene, XXXI, 4, 493.

Hopkirk, Dayus, Simpson and Grimmett. N.Z. Journ. of Agric. XL, 4, 226.

Leitch and Henderson, 1926. Biochem Journ. XX, 5, note added 1930.

Mason, 1933. Trans. N.Z. Institute 63, 373.

Marine and Lenhart, 1909. Arch. Int. Med. 3, 66.

McCarrison and Madhava. 1932. Indian Medical Research Memoirs, No. 23.

Orr and Leitch, 1929. Iodine in Nutrition. Medical Research Council.

Shore and Andrew, 1929. Goitre in School Children.