CHRONIC ZINC-POISONING OF PIGS.

New Zealand Journal of Agriculture, Volume 54, Issue 4, 20 April 1937, Page 216

CHRONIC ZINC-POISONING OF PIGS.

RESULTS OF EXPERIMENTAL FEEDING OF PURE ZINC

LACTATE.

R. E. R. Grimmett, I. G. Mclntosh, and E. M. Wall,

, Chemistry Section, and

C. S. M. Hopkirk, . Veterinary Laboratory, Department of Agriculture, Wellington. . In the New Zealand Journal of Agriculture for July, 1936, p. 34 (1), attention was drawn to the possibility that unthriftiness, arthritis, and mortality in young pigs may, in some cases, have been connected with the solution, in the skim-milk upon which the pigs were fed, of large amounts of zinc from the galvanized-iron piping used . for conveying the milk to the piggeries. In view of:the negative findings of American ’ investigators on the possibility of the existence of chronic zinc-poisoning, and also doubt as to the parts played by biological factors, and chemical substances other than zinc, in the causation of the disease, it was decided to institute experiments at the Wallaceville Veterinary Laboratory. ■ The Wallaceville Experiments. To ensure that conditions should approximate as nearly as possible to those obtaining on the farms where trouble among the pigs had been associated with the use of galvanized-iron pipes, and at the same time obviate possible uncertainties due to insolubility of zinc oxide and complicating effects of impurities such as lead, arsenic, or cadmium, it was decided to feed zinc in the form of lactate, prepared and tested in the laboratory for purity. Ten pounds of B.P. zinc oxide was obtained as a bulk supply, and showed on analysis the following results :—■ Lead, Cadmium. No trace of ’precipitate or darkening on passing H 2 S through a solution of 10 gm. dissolved in just sufficient hydrochloric acid to .effect complete solution and diluted to about 100 cc. A trace of lead acetate solution when added to this solution gave a pronounced black precipitate. No precipitate or trace of lead chromate on applying the test prescribed by the U.S.P. Arsenic. —No trace by Marsh test using gm. The zinc oxide was dissolved in. lactic acid B.P. (tested for heavy metals with negative result) and the precipitated zinc lactate, filtered off, dissolved in hot water, and allowed to crystallize on cooling. The snowwhite zinc lactate was then filtered on a buchner funnel and tested for acid-insoluble-sulphide metals with entirely negative results. Zinc Lactate Feeding to Pigs. Three young healthy weaners were ' selected from a litter of ten young pigs. The three were fed in a common trough with whole-milk and a little meal to which the zinc lactate previously dissolved in water was added. The milk contained approximately o-i per cent, of zinc as lactate.

The trial commenced on the. nth August and continued until the last pig was killed on the 4th November. On about , the 10th October —two months after the commencement of the feeding experiment—the pigs commenced to leave some of their milk, and the quantity was at once cut down. Just before “ going-off ” their food' the pigs were all noticed to be stiff in action. By the 13th October the pigs were noticeably lame, one much more so than the other two. They also appeared to be rougher in the coat and more flat-sided than their control litter-mates not receiving zinc. On the 23rd October it was decided to kill the pig showing'most lameness, while a second pig. died on the 24th probably due to the handling of the day before. The third pig, which was killed on the 4th November, was showing similar lameness to that of the others previously killed. It is estimated that the three pigs received the. following amounts of zinc lactate, assuming that each ■ had . drunk a similar amount of milk —.:. . s .. ‘ - . ■ " -.••• x , No. 1 pig, which died 23rd October, 1936, 804 gm. zinc lactate ißi-gm. zinc. \ ■■ " \ No. 2 pig, which died 24th October, 1936,. 824 gm. zinc lactate =. .- 185 gm. zinc. ’ . - < , > ' No. 3 pig, which died 4th November, 1936, 1,055 gm. zinc lactate --' j. 237 gm. zinc. /. . - >•. ' Post-mortem Examination of Pigs. ■ No. I. This was definitely the worst case, but no scouring had been observed. The blood had a thin watery appearance, but clotted exceedingly quickly. Heart, lungs, and pancreas appeared normal. There was no congestion of the alimentary tract and no evidence of scouring. The liver showed ,an obvious central necrosis .of lobules, , and was of a pale-brown colour. The kidney was rather tod brown in the’ cortex, and urine was tinged with bile.- / ... ! The chief changes, however, were noticeable in the ends ,of the humerus. ■* The head of the humerus in both legs showed a collapse of the bony structure beneath the, overlying cartilage. In one case there was erosion of the cartilage as well, and a definite lifting of that cartilage from the bone beneath. The ends of the bones , were weak and cancellous and suggestive of serious mineral deficiency. The synovial fluid was slightly blood-stained, and gave a growth of Streptococci and Staphylococci. No noticeable changes were to be seen at the ends of other long bones. Pig No. 2. — Found dead 24th October. Had been noticeably, t lame on the left foreleg but had not scoured. The heart, lungs, pancreas, liver,' and bladder appeared normal.. The kidney was pale and contained a gelatinous fluid in the pelvis. There was 'slight catarrh and congestion of the mucosa of the stomach, otherwise the alimentary canal appeared normal. Brain appeared congested. " The long bones were examined, and the only one noticeably bad was the head of the left humerus, which was similar to that of No. 1. The joint fluid gave no growth of organisms on culture. < ; Pig No. 3. — Post-mortem examination was made on 4th November, 1936. This was the largest of the three pigs, but was very lame in the

front legs. There had been no scouring, but the pig appeared unthrifty. All organs appeared normal, and no changes were observed in the alimentary canal.

Analysis of blood for. calcium and P 2 O 5 gave normal results, and blood histology showed no changes. Examination of the long bones revealed changes in the humerus in both forelegs and at the proximal and distal ends. The cartilage of the head of the humerus had lifted, and in . places showed definite erosion, while the bone was spongy. There was some erosion, and considerable fluid was present in the humero-radial joints. No organisms were recovered from the synovial fluid on culture. There was also in this pig a similar lesion on the head of a femur. . Microscopical Examination of Organs. .. . Liver. — In pig No. I a wide zone of cellular necrosis appeared round the central vein of the lobule, but in pigs Nos. 2 and 3 no changes could be observed. Pancreas. — In all three cases the pancreas was considered normal. The suggestion that a fibrous condition existed could not be confirmed when one considered the fibrous condition of the organs of normal pigs. Kidney.— No. 1 pig showed definite' glomerulo-nephritis, but the other two pigs showed only comparatively slight changes. Eosinophilic droplets were found to be present in the glomerular sacs in numbers, and passing through to the convoluted tubules. Lining-cells of the convoluted tubules appeared to be secreting excessively, so that long processes of . the cells jutted out into the lumen and appeared to deposit irregular droplets which took the haematoxylin stain. In. parts there had been an accumulation of debris forming blockages of the tubules. Where such casts had formed, erosion of the cells had taken place, and occasionally the basement membrane had ruptured. A cystic condition of a few of the tubules had resulted. Summary. Zinc lactate feeding of pigs resulted in lameness and unthriftiness. Damage occurred in one case in the liver and to some. extent in kidneys of experimental pigs. The humerus was badly damaged in each case, . the .. cartilage having lifted off a soft spongy underlying bone. This non-specific arthritis was the cause of the lameness, and was . produced apparently by an upset of mineral metabolism resulting from prolonged zinc feeding. Analytical Results on Biological Material from Wallaceville Pig-feeding .Experiments. A representative series of samples was collected from each pig as soon as it was dead, with special precautions to avoid contamination with zinc. The samples were immediately weighed and the analysis commenced 1 on the fresh material. Unfortunately the control littermate pigs were not available for killing at the time, so that to secure a basis for comparison the blood and organs of an ordinary pig killed at the abattoirs were secured and analysed. • Data on the zinc content of pig-organs was lacking in the available literature,' but comparison could be made with the figures for other

mammals, including man, cattle, dog, cat, horse, rabbit, and rat. The results of analysis of the pig-organs are given in the accompanying table : ■

. . Notes on the Toxicity of Zinc. The toxicology of zinc may be considered under three headings : (1) Acute poisoning due to the caustic or corrosive action of certain ■soluble zinc salts, especially the chloride and sulphate, on the alimentary •canal. This local action is well authenticated, and is not due to a general or systemic toxic effect of the metal or metallic ion. (2) 'Brass founders’ ague or metal fume sickness is an acute febrile ■condition resulting from the breathing of very finely dispersed particles of metal or oxide in the form of fume. Though generally associated with zinc it has been produced experimentally with other metal fumes, and is believed to be due to the local action of metallic particles of colloidal dimensions on the lung tissues causing denaturation of protein, which is absorbed, giving rise to a kind of anaphylactic shock. (3) Chronic or occupational zinc poisoning.

On this aspect there has always been the greatest degree of controversy. Most of the experimental work has been carried out with zinc oxide. The majority of investigators assume that zinc oxide isconverted to zinc chloride, lactate, or albuminate in the stomach or other parts of the alimentary canal, but several, such as Heller, consider that it is mostly passed through the intestine unchanged. The toxic effects obtained by certain investigators who have fed zinc oxide is attributed by later workers to impurities, especially lead,, arsenic, and cadmium. Others have fed considerable quantities without appreciable effect. Occupational disease is also generally assumed,, and, in some cases, proved to be due to these impurities, particularly lead. Dr. H. Engel(2) (Berlin) reviews this aspect in the publication on “ Occupation and Health, No. 353,” published by the International

Labour Office (1931). He considers that pure zinc has a toxicity, if any, similar to copper, and states that zinc ought not to be considered as an industrial poison exerting a general effect due to its absorption. On the other hand, he notes that Kunkel found 28 mg. per kilogram of zinc albuminate given by the alimentary canal to be fatal to the rabbit, and that J. Macht in 1931, by giving 0-5 gm. zinc oxide per kilogram to dogs and cats, caused repeated vomiting, wasting, and shivering, while on the rabbit 1 gm. of zinc oxide was fatal, and 20 mg. caused renal changes. In 1925 Mallory and Parker caused acute glomerulonephritis by injecting 0-5-1 gm. of powdered zinc (metal) under the skin. Kolbert found that non-caustic zinc salts on injection, cause paralysis of the central nervous system and vascular system and muscles.

Batchelor, Fehnel, Thomson, and Drinker.(3) carried out a comprehensive clinical and laboratory study of the . health of workmen in a zinc-smelting works at Palmerton, Pennsylvania. The New Jersey ore used in this works was very low in lead, cadmium, and arsenic. It was found that fifty-one zinc smelters in perfect health excreted each up to 3-9 mg. of zinc per 100 cc. in the urine and up to 133 mg. in the total faeces daily. The amount involved was thus not of an excessively high order, although continuing over a long time. There were no pathological findings.

Drinker, Thompson, and Marsh(4) in 1926 fed cats and dogs with daily doses of zinc oxide of 0-175 gm. to 1 gm. for periods of from three to fifty-three weeks. All three cats on the highest dose (1 gm.) exhibited at autopsy gross hardening and. nodular development of the pancreas, which was overgrown with fibrous tissue partially eliminating the islets. The authors did not attach any significance to these findings, as they considered this dosage greatly in excess of any likely to •occur in practice. The animals on all other dosages remained healthy, and showed no damage to any organs on autopsy. The evidence submitted does not indicate that more than a very small fraction of the zinc oxide fed was assimilated. Similarly, Heller and Burke (5) fed rats with amounts of zinc salts of 0-25 per cent, and 0-5 per cent, of zinc in the diet. It is stated that no toxic' effect was observed over several generations. . The figures appear to indicate, however, a higher mortality of young in the group on the higher zinc ration. The analytical results showed that no increase of zinc in the organs had taken place, and no evidence was presented indicating that absorption of zinc had taken place from the zinc oxide in the alimentary canal. Discussion. The results of the present experiment are clearly at variance with those performed elsewhere, and on which the opinion has been expressed that zinc, apart from the local caustic action of certain zinc salts, is a non-toxic metal, or has a toxicity, of an extremely low order. To account for the differing results the following points may be considered : (1) In the majority of experiments where zinc has been fed to animals over long periods the zinc has been in the form of the oxide. There is no evidence that other than a small fraction of this insoluble compound when fed to. animals is rendered soluble by the digestive juices and absorbed. In the few cases where the soluble mineral salts have been fed, it is possible that their local action on the absorbing surfaces of the alimentary canal has tended to hinder absorption and to promote expulsion. (2) The pig may be an animal peculiarly susceptible to zinc poisoning. It is well known that animals vary in their reaction to various poisons. (3) The amounts of zinc fed have been comparatively large, although within the range of possibility for animals under farm conditions, as •demonstrated by numerous analyses of milk which have been collected from installations where lengthy galvanized-iron pipes are used.

(4) The effects —at least so far as the bone lesions are concerned — may be principally due as suggested to an upset of mineral metabolism. Further experiments are in progress using half and quarter the amount of zinc to determine at what level demonstrable effects appear in the'pigs. A recent report indicates that no further trouble has been experienced on the farm at Atiamuri, where the first case occurred, subsequent .to the removal of the zinc .from the pipes, although conditions are. otherwise unaltered. Acknowledgment. The authors wish to thank Mr. D. H. Le Souef, Veterinarian, Wellington, for assistance •in obtaining normal pig-organs. The illustrations are from photographs taken by Mr. A. L. Bryant. . References. • (1) Grimmett, R. E. R., and Mclntosh, I. G. : Suspected Zinc Poisoning in Pigs. N.Z. Jour. Agric., 1936, 53, 34. (2) Engel, H. : Zinc. '■ Occupation and Health, No. 353, 1931 (?). International Labour Office. - - . ' (3) Batchelor, R. P., Fehnel, J; W., Thomson, R. M., and Drinker, Katherine R. : ■ A Clinical and Laboratory Investigation of the Effect of Metallic Zinc, of Zinc Oxide, and of Zinc Sulphide upon the Health of Workmen. Jour. Industrial Hygiene, 1926, 8, 322. (4) Drinker, Katherine R., Thompson, Phebe K., and Marsh, Marion : An Investigation of the Effect of Long-continued Ingestion of Zinc, in the Form of Zinc Oxide, by Cats and Dogs, together with Observations upon the Excretion and the Storage of Zinc. Amer. Jour. Physiology, 1927, ' 80. 31. (5) Heller, V. G., and Burke, A. D. : Toxicity of Zinc. Jour. Biolog. Chem., ' . . . 1927, 74, 85.

♦Doubtful; amount of material available insufficient for accurate determination. f Exact ffigure somewhat doubtful; material all used. ■

.. — Pig No. i. Pig No. 2. Pig No. 3. Normal Pig J/943Mg. in i kg. of wet weight— Blood .. ... I2-O* ' 6-5 8 • I 4'49 122nd Sept.) 8-3 (22nd Sept.) 20-5 (22nd Sept.) 12-3 4'9 Heart .. .. (22nd Sept.) 8-3 (23rd Oct.) 6-8 • (22nd Sept.) 20'5 (24th Oct.) 9’4 (22nd Sept.) 12 • 3 (23rd Oct.) 13 • 3 (4th Nov.) 6-7 . 4'9 Spleen ' .. ... 23’5 113-6 24-6. 19-5 Brain .. .. 12-0 14-3 12-9 ' . Lung . .. . .. 12’7 14 • Pancreas . . .. I9O-O 610-o 187-8 51-0 Bile 51-5 55-9 6-o Joint fluid .. .. II -o . 18 -o* Ovaries .. .. 19-3 Muscle .. 32-0 29-0 29 • 0 Kidney .. . . 1 , 000 • 0 i,57°-°t 6io-o 27-0 Liver .. .. I,020-0 730-0 1,140-0 155-0 Mg. in 100 cc. urine 0-17 o-9 o-55 0-15 (26th Sept.) 0-35 . (20th Oct.) o-6 . (26th Sept.) o-45 (20th Oct.) 2-17 ' (26th Sept.) 0-27 (19th Oct.) 0-27 Mg. in i kg. of ash Bones . . . . (26th Sept.) o- 35 (20th Oct.) o-6 (23rd Oct.) (26th Sept.) o-45 (20th Oct.) 2-17 (24th Oct.) (26th Sept.) 0 • 27 (19th Oct.) 0-27 (20th Oct.) 0'33 1 ’ • (4th Nov.) (24th Oct.) (20th Oct.) °‘33 (4th Nov.) Humerus (lower end) . . 2,276 1,844 1 ,102 251 Femur (lower end) 1,202 i,33o 906 Humerus (shank) .. 597 828 623 193 Femur (shank) 260 720 •486

Table showing Zinc-content Determinations in Wallaceville Pig Experiments.