An Iodine Survey of New Zealand Live-stock Part III. Sheep of the Canterbury District.

By Ethelwyn Mason and D. F. Waters.

Greater variation is shown between the two years in which the samples were collected. The 1934 samples from the northern part of the district under survey contained about one-half the iodine of the 1933 samples. The figures are incomplete, since, unfortunately, the collection of samples was discontinued after March. 1934, as it was then considered that sufficient representative samples had been collected. This yearly variation is the main reason for the low figures obtained from the north, as the majority of the samples here were collected in 1934. The weather records for the district show that during the 6 months prior to April, 1934, much more rain fell than was the average and about twice as much as in the period prior to April, 1933, which was a dry season. Since the few samples received from Canterbury during 1934 gave much the same results as those of the previous year, it is doubtful whether the difference in rainfall between the two seasons is the cause of the lower values for iodine in the north during 1934. The river-flats which are common in that area, may, however, be more affected than the open plains by the increased rainfall. No correlation could be obtained between iodine values and average yearly values obtained from a rainfall map of the area. The areas of highest rainfall are the foothills, whence came but few of the samples. The variation in rainfall over the plains from 25 inches near the coast to 35 inches at the foothills is but slight. No other reason is submitted to account for the variation in iodine-content between the glands collected in the two seasons.

As the purpose of this work is a survey of the iodine in the glands collected in the district, the results have been tabulated according to river basins or other naturally bounded areas, as they occurred.

Waiau-Ua River (Table IV).

The 1933 samples were all taken from plains and river-flats. The neighbouring hills are mainly Trias-Jura, though C1410 and D247 approach a belt of Miocene. None of the samples is below the critical value of -10 per cent, iodine. D1087 is the only case where licks other than rock-salt have been used, and no information was received as to its iodine-content, if any. Rape is commonly used as supplementary feeding, and sometimes turnips and kale. ManuriaJ treatment is usually confined to the dressing sown with the foddercrops, and is generally superphosphate. Sometimes lime is added. and a few farmers prefer proprietary lines of fertilizers mixed to suit the crop grown. This supplementary feeding-practice and manurial treatment applies in general to the whole of the area surveyed. Farms in the remote western valleys near Hanmer receive up to 50 inches of rain per annum. This rapidly decreases to 30 inches at Waiau and then rises again to 35 inches towards the coast.

The 30 samples from the area taken in 1934 illustrate clearly the difference between the two years. The mean for the year is only .11 per cent, iodine, which is about half that of the 1933 samples. The values range from 04 per cent, to a maximum of 19 per cent, compared with a variation of from 11 per cent, to 32 per cent, for 1933. Half the samples are below the critical value. The

samples D1153, D1317 and D1436 are from the same farms as C1374, C1410 and C1449 respectively, and show similarly lower iodine values throughout. Five of the samples were from stock fed iodised licks. None of these glands contained notable quantities of iodine, but it is interesting to note that none were below the critical value when so many of the other samples were deficient. The farming practice as regards crops and manuring was the same as in the previous year. The actual rainfall for the six months prior to April, 1934, was approximately double that of the corresponding period of 1933.

Hurunui River (Table V).

This river flows from Trias-Jura mountains across alluvial flats, then through Trias-Jura again and finally between Trias-Jura and Miocene formations to the sea. Most of the samples come from the wide river-flats about Culverden and Medbury. One deficient sample was received from the area among the 16 samples taken in 1933, and was from Miocene hills at Greta. Two neighbouring samples, C1041 and C1271, have a-much higher iodine-content, and are taken from similar hills nearer the sea. The mean value for all samples, 19 per cent., is about normal. The 1934 samples average only 12 per cent, iodine. All are taken from plains and river-flats, and most are from round Culverden and Medbury. Again in this case all the lambs where licks were fed had glands with more than the critical iodine-content. One sample, D1525, from Hawarden had only 01 per cent, of iodine on the dry weight, and is the lowest from the Canterbury district. The average dry weight of these glands, 1.08 grams, is by no means abnormal, as. would have been expected. The rainfall is 40–50 inches at the edge of the foothills. It decreases rapidly to 30 inches over the alluvial plain, and then increases to 35 inches again near the coast.

Waipara River (Table VI).

This river rises in mountains of Trias-Jura rock and flows through foothills which gradually decrease in size to the sea and are based on belts of Miocene and Cretaceous formation. Most of the farms samplied lie to the north of the river and adjoin those of the Hurunui River. The nine samples received in 1933 were all taken in April, and have a fairly high, iodine-content of 24 per cent. The 1934 samples were all taken in February and March, and have about half the iodine-content of the 1933 samples. Only two were below the critical value, but the rest of the glands were uniformly low. The one lick-sample does not show any result from the extra iodine. The average rainfall for the area decreases regularly from 50 inches in the hills to 30 inches at the coast.

Kowhai River (Table VII).

This is a much smaller river which rises in the foothills and flows across the northern end of the Canterbury Plain. There is a resemblance between these results and those from the larger river areas to the south. One sample in the ten is low and the rest vary from 10 per cent, to 30 per cent, of iodine for no apparent reason. The rainfall is low, being from 35 to 30 inches per annum.

Ashley River (Table VIII).

This river rises in the higher foothills of Trias-Jura rocks and then flows across the alluvial plain. A few miles to the north a wide belt of Miocene rock runs parallel to the river. With the exception of D1452 and C1162, D1328 and D305, which represent two farms on Trias-Jura well up near the source of the river, the hill samples are from the Miocene belt. The rainfall decreases steadily from 50 to 60 inches received by the two farms mentioned to 30 inches at the coast. None of the samples collected in the two years was below the critical value, and the average for each year is the same. Of the lick-samples D1187 is the only one above the average in iodine-content. The district compares well with the rest of the area surveyed.

Waimakariri River (Table IX).

This is a large river flowing across the alluvial plain, on which all the farms sampled are situated. Six samples of the 49 received in two years were below the critical value. D128 Kirwee, D263 Courteney and D431 Aylesbury are situated close to the south bank on the lower reaches of the river, which, is well known in the country, for its severe floods. D227, at Springfield, is also close to the river. D431, with an average dry weight of 1.78 grams, approaches double the normal size, though in no way goitrous. The wet weight averaged 6.75 grams. Two samples only were from lick-fed stock, one of which, D128, has already been mentioned as deficient. The lick fed in this case was a proprietary one which the owners vary in composition to suit the area supplied. It is possible that in this case the lick contained but little iodine. D377 is from a property where three other samples were taken (D138, D330, D458), and there is nothing to explain why this one sample should have the high iodine-content of 45 per cent. The rest of the samples appear to be normal and show little difference over the two years. The rainfall varies from 50 to 30 inches on the coast.

Banks Peninsula (Table X).

This is composed of steep hillsides of basic igneous rock overlain to some extent by loess from the plains to the westward. Soil derived from such rock-formation is described as being relatively abundant in iodine, and this is borne out by the samples from this area, which have the high average of 26 per cent, iodine. Only two samples have less than 20 per cent., one from Kaituna (C967), where possibly the lambs may have been grazed on the adjoining alluvial flat, and one from Paua Bay (D303), east of Akaroa. The lack of iodine in the latter is quite inexplicable, since the farm differs in no known way from others in the district. The rainfall varies from 40 inches inland to 35 inches on the coast. In this district few supplementary crops are grown, only one farm providing turnips. No licks were used. Although glands from this district have the highest average iodine-content for the area surveyed, they do not approach the values recorded by Sykes for limestone country

in Wairarapa, which gave an average value of 35 per cent, for 21 samples, while 13 samples from greywacke gave 31 per cent., and 21 samples from papa gave 27 per cent, iodine.

Selwyn River (Table XI).

This is a small rain-fed river which, after crossing the plain, empties into Lake Ellesmere. All the samples are from the plain except D218, which is from the Trias-Jura hills close to D194 and D432 in the Waimakariri area. This sample was from lambs fed iodised licks and is slightly higher in iodine than the two samples mentioned. Another treated sample is D379, from Lincoln, and this also has a high iodine-content. Only two samples in 33 have under the critical value for iodine, C1154, from Irwell, close to Lake Ellesmere, and D434, Aylesbury, from the middle of the plain. The average for the area, 22 per cent., is fair. The rainfall varies from 40 inches near the hills to 30 inches on the coast.

Rakaia River (Table XII).

This is a large glacier-fed river from the Southern Alps. Samples were received only from the plains along its lower course. The area appears to be average for alluvial country, averaging 20 per cent, iodine. Only one sample, D185 (26/4/33), from Dromore, was below 10 per cent, iodine, and gave a figure, 05 per cent., which is much lower than an earlier sample, C964 (19/1/33), 24 per cent., from the same farm. The rainfall varies from 40 to 30 inches.

Ashburton River (Table XIII).

This is similar to the Rakaia River, though not so large. All samples are from the plain and gave a good average figure, 23 per cent, for iodine. Five of the 39 samples had low iodine-values, four being just below the critical value and one from Tinwald (C1334) very low. One of these low samples was from lambs having access to an iodised lick. The rainfall varies from 50 to 30 inches.

Hinds River (Table XIV).

This is a smaller rain-fed river from the foothills. The average iodine-content of the glands is lower than that of those from the rivers immediately to the north, and four samples in 25 had low iodine. Two samples were from lambs fed with a proprietary lick which may not have had a significant iodine-content, since one sample was below the critical value and another was just above it. A third iodised lick-fed sample gave a value of 37 per cent, iodine. The rainfall ranges from 40 to 30 inches.

Rangitata River (Table XV).

This is another large glacier-fed river similar to the Rakaia River. All the samples are from the plains, and their average approaches that for the Hinds River samples. Four of the samples were from lick-fed lambs, and one of them, Montalto, gave the high

figure of 45 per cent, iodine. Another of these (D265, 04 per cent.) was from Rangitata Island, where the soil is described as a sandy loam over gravel. A second farm 0n the Island was sampled, and though apparently not lick-fed, gave a value of 12 per cent, iodine. The rainfall varies from 40 to 30 inches.

It may be mentioned here that the soils of the area bounded by the Rakaia and Rangitata Rivers, and including the Hinds and Ashburton River areas, were very carefully surveyed by Dr L. I. Grange, of the Geological Survey Division. Sixty-five of the thyroid samples from this area could be identified as from specific soil-types. The numbers given in the last column but one of Tables XII–XV are those of the types enumerated by Dr Grange.

Nine samples (excluding two lick-samples) were from type 5, the Ruapuna stony silt loam. The highest value was 20 per cent, iodine; the lowest 04 per cent; with an average of 14 per cent, and weight 94 grams per gland. Ten samples from type 7, Buccleugh stony silt-loam and stony loam, averaged 22 per cent, iodine, weight 69 grams. No deficient sample was received, the lowest being 14 per cent, and the highest 34 per cent, iodine. Of type 12b, Seafield silt-loam, stony phase 2, six samples were analysed and found to vary from 09 per cent, to 34 per cent. Average 22 per cent, iodine, weight 86 grams. Type 13, Lismore stony silt-loam, was represented by 9 samples, two being 09 per cent, and the highest 29 per cent. Average 15 per cent, iodine, weight 88 grams per gland. The rest of the types had only two or less samples each. Summarising the types more broadly, 43 samples from weakly podsolised soils gave an average of 18 per cent, iodine, weight 83 grams, and included 7 deficient samples. Twenty-one samples from skeletal soils had an average of 20 per cent. iodine, weight 83 grams, and included two deficient samples. It will be seen that the difference between the types 5, 7, 12b and 13, representing the podsolised soils, exceeds the difference between the average for this class and that of the skeletal soils. It was concluded that many more samples would be necessary before any connection could be demonstrated between soil-types and iodine-content of glands. For this reason only the very broad classification of river-flats and plains has been used to subdivide the alluvial soils.

Opihi River (Table XVI)).

This is a small rain-fed river rising in Trias-Jura country, flowing through an alluvial flat about Fairlie, then through a belt of Trias-Jura and Miocene and finally across the narrowing southern end of the Canterbury Plain. Twenty-two samples were received from the district. Two from alluvium were below the critical value. The average value was 21 per cent. iodine, but this included D481, whose figure, 70 per cent. iodine, must be regarded with suspicion. One of the two lick-samples included has a reasonably high figure. The rainfall varies from 40 inches at Fairlie to 25 inches on the coast.

Timaru (Table XVII).

This is a small district on the coast with a very light rainfall of 25 inches per annum. Here the plain is broken by low hills of basic igneous and Miocene rock. The five samples received indicate that the district resembles Banks Peninsula in the amount of iodine available.

Pareora River, Coast, and Waihao River (Table XVIII).

From Timaru southwards towards the Otago boundary the rivers become smaller, and for convenience all the samples have been grouped together. The hills in the area are either Trias-Jura or Miocene. Two samples from the narrow alluvial plain are below the critical value. Only one of three lick-fed samples appears to be high in iodine-content. The rainfall varies slightly from 30 to 25 inches per annum.

Summary of Districts (Table XIX).

In reviewing the results set forth above it may be said that no grossly enlarged or goitrous glands were received from the district. While most of the glands had an iodine-content above the critical value of 10 per cent. on the dry weight, scattered samples were found to fall below this figure without the size of the gland being unduly affected. No type of soil or country may be definitely associated with low iodine-content except the river-flats of the Waiau-ua, Hurunui and Waipara districts, which gave a low iodine-value only in the 1934 samples. A few scattered samples taken from river-banks, e.g., the three from the Waimakariri River, show a tendency to be low in iodine. Only in a few cases did stock provided with iodised licks show definite evidence that the licks had been taken and the iodine-content of the glands increased. Frequently the lick fed was a proprietary compound which is said to be altered by the makers to suit the mineral requirements of a district. No doubt in many cases where this lick was used the iodine-content of the lick did not justify the description as an iodised lick. Another factor which interferes with the results from feeding licks is the extreme solubility of potassium iodide and the leaching effect of rain upon the blocks in the field. No conclusions may safely be drawn from these results in regard to the feeding of iodised licks. Special experiments such as are being conducted in Southland are essential if useful data are to be obtained.

The dry weight of the glands have been given throughout the tables and the percentages of iodine calculated on these weights. In general the weights of the glands vary inversely with the percentage of iodine in the gland as has been reported by other workers.

Summary.

A large number of thyroid glands from lambs of the Canterbury Province, New Zealand, have been analysed for iodine-content by the method of Leitch and Henderson (1926). The results have been grouped according to the geological character of the country. The average values for the iodine-content of glands from the main types are:—

The results have also been grouped in the districts from which the samples came.