BUSH DISEASE.

New Zealand Journal of Agriculture, Volume 3, Issue 5, 15 November 1911, Page 394

BUSH DISEASE.

B. C. Aston,

F.I.C.

The evidence adduced by Veterinary Officers of the Department over the period of fourteen years that they have been cognisant of the matter goes to show that the condition in stock known locally as “ bush disease ” or “bush sickness ” which occurs -in the Rotorua, Matamata, ’ and Tauranga Comities (long. 176° E., lat.- - 38° •■s.).-■ is not a disease in the proper sense of the term, but a physiological condition resulting either from — (a) a food-supply wanting or deficient in-some essential nutrient, which therefore results practically in-starvation ; or (6) a food-supply containing naturally or adventitiously (1) some toxic compound, or (2) some, normal constituent present in abnormal quantity, resulting in chronic poisoning. Assuming, therefore, that the pathologists have satisfied themselves that there is no abnormal; micro-organism present; that there .is- no sign of acute disease in a wasting animal (which commences to recover as soon as it is removed on to unaffected country) ; that the disease is not communicable to other (healthy) animals either by contact or by transfusion of blood or by other inoculation tests ; and that the sickness is confined to a definite area of country outside of which it does not spread, but on which it always in time develops in cattle and sheep, the problem must be one connected with the food-supply, and therefore one for the chemist to elucidate by research. The following questions naturally suggest themselves : (1.) Is there any poison present in the animal, in the food, or in the soil ? (2.) Whether such poison (if present) is there in amounts which would be injurious under the conditions . prevailing on the “ sick ” country. (3.) Is there a want of balance in the food-constituents, organic or inorganic, which would result in the condition complained of ? Bush sickness has been described by Professor Gilruth as “ progressive anaemia.’’ Specimens of the dried blood, (including clot and serum) of cattle analysed have always shown a great increase in the inorganic salts of unhealthy over those of healthy blood ; or, to put it in what is physiologically a better manner, there is a diminution in thejorganic matter of the unhealthy blood compared with healthy blood. In the unhealthy blood there is roughly only half the normal amount of iron-oxide, and

greatly diminished amounts of phosphorus and potash, the characteristic inorganic constituents . of. the blood-cells (corpuscles). The chemical analyses point strongly to a deficiency of the blood-cells. Blood-counts by Mr. H. A. Reid, F.R.C.V.S., show conclusively .that anaemia is always present in animals suffering from “ bush sickness.”

What causes this anaemia ? The conditions already described point to something connected-with the food-supply as the -cause. Now, the foodsupply is the last thing that the farmer would suspect, consisting mainly, as it does, of a luxuriant growth of cocksfoot and red and white clovers -staple fodder-plants upon which., thousands of stock are yearly successfully raised both in this and in other countries. Stock may, moreover, apparently suffer and die from the sickness -either in paddocks where there is .nothing but red clover or where there is little but cocksfoot. This would seem to discount the possibility of an organic compound being the cause, as one would hardly imagine the same organic poison being formed in two such widely separated families as Leguminosoe and Graminece. In the event, however, of some poisonous element occurring in the soil in a form which would allow its compounds to be taken up by the plant, it is possible that an inorganic poison might be the cause. The nitrogen-content of the hay and grass from the affected country negatives the idea that there may be a deficiency of proteids in the grass. The inorganic-food ratio requires further investigation ; but the fact that young animals from other districts experience a decidedly beneficial effect from the change, and may be fattened on the .suspected pasture if not kept on too long, does not afford much hope for the suggestion that there may be a deficiency in any of the necessary nutrients, organic or inorganic.

Concerning the proper ratio of inorganic foods for stock, little is - definitely known. It has, however, been clearly demonstrated by Bunge that all purely vegetable feeders, including some races of men, require a mineral ration which includes salt (sodium-chloride). He considers that • • •• • i ' the sodium salt is necessary to eliminate the potassium salts taken up with the vegetable food. Salt is, of course, known to be a necessity in keepingstock in the best. condition. Boussingault experimented with six oxen, three of which had salt and three had no salt. In the course of the second month the difference in the two lots was visible even to the unpractised eye. The hair on the oxen which had salt was smooth and shiny, and on the other lot it was dull and erect. After a year the signs were still more prominent. On those which had no salt the hair was matted and the skin in places devoid of hair. Those which, had salt, on the contrary, retained the look of stall-fed beasts. Their briskness and frequent indication of a desire to leap contrasted strongly with the heavy gait and cold temperament observed in those which had no salt. It would be interesting to know the ultimate condition of stock continuously fed on a ration deficient in sodium salts and as rich in potash as is the herbage of the unhealthy country

Would a condition in any respect resembling bush sickness result ? Could this be referred to such a cause it would be fairer to attribute the sickness to unsatisfactory farming than to any defect of the soil or food.

Any variation in the food is probably due to a variation in the composition of the soil: hence analyses of the soils might afford valuable information. But here we are met by this fact: The mineral (inorganic) constituents of the soil are not taken up by plants in the same ratio as they occur in the soil. The plant selects certain constituents in preference to others. Thus silica, alumina, and the iron-oxides are the most abundant constituents of the soil, and of the weak acid (1 per cent, citric acid) extracts of -pumice soils, but, although these three constituents total some 80 per cent, of the soil, the clover ash only contains some 20 per cent, of them ; but, on the other hand, the ash contains some 27 per cent, of potash, which only exists to the extent of 1 or 2 per cent, in the soil. This selective action of plants extends to other elements, at least one* of which may be toxic.

So far as one can learn, there is no other country having similar soils under similar climatic and agricultural conditions ; but the writer is open to correction on this point, and would be glad to learn whether any similar unhealthiness has appeared on pumice soils growing cocksfoot and clovers in a temperate climate with a rainfall of 50 in. in other parts of the world. Soils are almost invariably formed by the weathering and disintegration of rock, a slow and gradual process whereby much of some of the original constituents of the rock is dissolved out and washed away in the drainage-water. The soils of this “ sick ” country,, on the contrary, have not been weathered to the same extent. They are invariably soils consisting largely of pumice and other ejectamenta comparatively recently blown out of the bowels of the earth, and scattered by the wind over a large area of country. Pumice is an’acidic (containing a large excess of silica or silicic acid) lava which has been frothed up when in the molten state, and so intimately mixed with the gases of the volcano that the apparent specific gravity of the rock is very much lessened, and, owing to the entangled gases, the solidified pumice is enabled to float on water, or to be wafted considerable distances by air-currents. It is a well-known fact that recently ejected volcanic mud will not grow crops until the sul-

phides, which are poisonous to crops, have been oxidized into harmless sulphates. It is possible that pumice will not grow animals from some similar reason.

In investigating an obscure disease one must not expect immediate results, or be impatient if some definite answer is not at once forthcoming from experiments. In a case such as this, where the onset of the ailment is so long delayed, taking perhaps months, it is only reasonable to suppose that the abnormality in conditions which is the cause is not very greatly removed from absolute normality, and it is this fact which inspires most hope that a practicable remedy may be found — by altering the animals’ diet in some way the cause of the wasting may be counteracted. Mr. Clinkard has satisfied himself that by adding a certain amount of bran,, a substance very rich in inorganic (mineral) food, the trouble may be postponed but not altogether avoided. Now, if we can find by experiment which particular organic food it is that caused this desired effect, we may be able to apply that food in some more concentrated form and so obviate the present injurious results of feeding on the affected pastures.

Field experiments, including the feeding of sheep and cattle on pasture which has been dressed with various kinds of fertilizers, are being conducted according to schemes recommended by me on four farms in the unhealthy country. On one of these no salt is supplied as a “ lick ” for the stock. On other two salt is supplied ad libitum to every paddock, including in one case the control paddocks, this being only what is consonant with good farming. On the fourth farm the pasture has been laid down with salt as a top-dressing.

One often meets with the question, Why should ruminants be affected and non-ruminants always remain perfectly healthy ? Perhaps the most suggestive fact which may be quoted in endeavouring to elucidate this aspect is the great difference in the time taken to digest the food in the two classes of animals —four or five days in ruminants, and less than half this time in non-ruminants.

In concluding this report I would ask the settlers of the district to hide nothing, and to render . what assistance they can to the departmental officers who are endeavouring to fathom the problem. It has been actually denied in the public Press that any trouble exists. Any such attitude of secrecy or of dissimulation on the part of those interested must hinder the work of the Department and render 'more remote the possibility of a solution. To those who may carp at the want of finality in the reports on “ bush sickness ” I would refer these facts : That obscure diseases in human beings have taken commissions of experts giving their whole time to the matter years of work to discover the causes, and it is unreasonable to expect an immediate result in the case of diseases of animals. It is barely twelve months since a sufficient sum has been voted for the purposes of the research.

* The term “ bush sickness ” is quite a misnomer. The condition may develop on land that has been cleared of bush or forest for over twenty years.

* Copper is the element here referred to. The liver of a sheep suffering from “ bush disease ” . always contains an amount of copper which is abnormally high when judged by the experience of European authorities, but investigation has shown that this is an abnormality shared with healthy sheep killed for consumption in other parts of New Zealand, there being found as much as 0-065 per cent, in two healthy sheep examined. By adding copper-acetate to the food of another from the same flock, in three months’ time the copper-content of its dried liver (healthy) was found to be 0-417 per cent., others of the same flock remaining healthy under the same dosage. Erom-0-02 to 0-04 per cent, of copper (Cu) —calculated on the liver dried at 100° C.—is apparently quite a usual amount to find in healthy sheep of the North Island. “ Sick ” cattle have not such a high copper-content, and are sometimes in accord with what is accepted as normal.