THE SORREL-POISONING THEORY OF LAMB MORTALITY.

New Zealand Journal of Agriculture, Volume XXXVI, Issue 3, 20 March 1928, Page 153

THE SORREL-POISONING THEORY OF LAMB MORTALITY.

C. S. M. Hopkirk,

B.V.Sc., Officer in Charge, and D. A. Gill, M.R.C.V.S., D.V.S.M.

Assistant Officer in Charge, Wallaceville Veterinary Laboratory.

As is generally known, a theory was recently advanced in Southland to the effect that the commonly occurring mortality among fat lambs is caused by sorrel poisoning. In view of the statement made, and quoted in the press, that proof of this theory had been obtained,, it is deemed advisable to publish the attitude of the Department of Agriculture towards it, and some account of relevant experiments made at Wallaceville.

The evidence on farms where the mortality occurs is quite against the theory ; but since odd plants of sorrel are to be found in almost .any pasture, and as there is in sorrel a salt of oxalic acid which affects the kidneys, it was thought well to go into the matter experimentally. .Sorrel itself is not poisonous, but the oxalate contained in it if taken in sufficiently large amounts damages the lining of the stomach and bowel, and causes inflammation' of the kidneys (the organs which ■excrete oxalates from the system). Hence it was decided to experiment with rabbits and lambs by the following methods : (i) Injecting ■doses of oxalate solutions into the veins ; (2) giving doses of oxalates by the mouth ; (3) feeding sorrel. EXPERIMENTS ON RABBITS. So far as the rabbits were concerned, death could easily be induced by injecting about forty grains of sodium oxalate in solution into the stomach through a tube. This was fatal in under three minutes

in one case, but neither with the naked, eye nor with the microscope, could any abnormality be discovered in the kidneys. Another rabbit was killed by giving it a series of injections of oxalate solution into the veins. In this case there were changes in the kidneys that were readily detectable with a microscope, and crystals of oxalate could also be seen in the kidney-tubules ; but the type of change noted was different from that seen in lambs whose kidneys are “ pulpy ” ; moreover, in the so-called “ pulpy kidney ” of lambs one does not find oxalate crystals. A third rabbit, which had been fed on sorrel only, for a week,, without showing any signs of illness, was killed and examined. No abnormality was found; the kidneys were normal and showed nocrystals. EXPERIMENTS ON LAMBS. In these tests six lambs were used, with the following results : Lamb No. 4A : This lamb, about seven days old, was given a series, of injections of sodium oxalate into the veins. When about 10 grains had been given, at the end of the second day, the lamb died suddenly. Examination showed the kidneys to be enlarged and pale. Microscopically there were changes like those noted in the rabbit similarly treated, and here again oxalate crystals could be readily seen in the kidney-tubules.

Lamb No. i : This animal, about six weeks old, was fed with dosesof oxalates and oxalic acid, and : allowed to run with its dam. In the course of ten days, it had received 56 grammes of these materials and was markedly ill. .It showed none of the symptoms seen in cases of pulpy kidney, however, its illness evidently being due to inflammation of the stomach and intestines. It was then given a single large dose of oxalic acid, and died quietly about an hour later. On examination the kidneys were found seriously affected. Small haemorrhages had occurred in them, giving a mottled appearance ; they were also enlarged, but there was no pulpiness, although the examination was purposely left till four hours after death to give this every chance of occurring. Microscopically it was seen that the kidney - tubules were badly damaged and contained very numerous crystals of oxalate. The haemorrhages had taken place exclusively into these tubules, which is another small point of difference between oxalate poisoning and pulpy kidney.

Lamb No. 5 : This was two to three weeks old, and was treated, similarly to lamb No. 1. In five days it received 34 grammes of potassium oxalate and 9 grammes of oxalic acid. It was then killed by a large dose of the latter, and examined some four hours later. The kidneys were certainly damaged, but to a far less extent than in No. 1. The changes that had occurred were of a similar nature.

•Lambs Nos. 2 and 3 : These were about five weeks old, and were fed on a diet entirely limited to sorrel, except for about ten minutes night and morning, when they were allowed to suck their dams. Feeding was commenced on 17th November, and for the first three days sorrel in the flowering stage was given, but from the 20th onwards, young leafy sorrel from a field under crop was gathered for them. They were hand-fed. three times a day, and ate on the average about 12 oz. to 16 oz. each per diem. This was continued for over four

weeks (until i8tb December), and during that whole period neither lamb showed any sign of illness or distress, save that each had a transitory attack of diarrhoea lasting two days (No. 2 on 5th December and No. 3 on 29th November). The lambs were both killed a week after sorrel feeding had been discontinued, and a careful examination was made. Microscopically there was evidence that damage to the kidney-tubules had occurred of a similar nature though to a much slighter degree than was seen in Nos. 1 and 5. Moreover, a few oxalate crystals could be detected in No. 3.

Lamb No. 6 : This was fed sorrel that had been mashed down in boiling water, and afterwards made to drink the water. A double handful of young sorrel-leaves was given in this way twice daily from 21st November to 18th December, without any ill effects being noticeable during that period or afterwards. The lamb was two to three weeks old when the experiment commenced.

COMMENTS.

Probably a perusal of these records will of itself be sufficient to show that oxalate poisoning is not the cause of the lamb mortality in the field, but a few additional comments may be made.

(1) Lambs Nos. 2 and 3 received far more sorrel than they could possibly have picked up for themselves when grazing an ordinary paddock. Further, although the oxalate present in the sorrel diet was sufficient to cause damage to the kidneys, far from causing sudden death it was not attended by illness of any sort.

(2) In none of the lambs experimented on was there any “ fluid round the heart ” or staining of the heart’s inner lining, both of which conditions are constantly found in cases of pulpy - kidney disease as met with naturally.

(3) The changes produced in the kidneys by the oxalate treatments and the disease are somewhat alike, but by no means identical.

(4) The behaviour of a lamb after receiving large doses of oxalate (e.g., lamb Nd. 1) is quite different from that of one suffering from pulpy-kidney disease.

(5) Samples of urine from cases of pulpy kidney in Central Otago were forwarded to the Department's Chief Chemist, who was unable to find any oxalates in them, whereas in samples from lambs 1 and 5 he found comparatively large amounts present.

(6) We did not find that lambs, even when hungry, showed any liking for sorrel, and while odd pieces might be eaten promiscuously with the other herbage, these experiments have - shown that such small quantities are entirely harmless.

Nature of Pumice. — Pumice is a solidified volcanic froth. It contains all mineral food required by plants, but most of this is in an unavailable state, as it has been fused to a semi-vitreous condition. By the aid of organic matter and such farming operations as produce compaction of the soil and the incorporation of organic matter, pumice may be slowly decomposed. Green manuring is the best of all methods for improving pumice soils.— B. C. A.