ZINC-POISONING IN PIGS

Hawke's Bay Herald-Tribune, Issue 98, 12 May 1937, Page 15

ZINC-POISONING IN PIGS

N.Z. Experiments Into Causes UNTHRIFTINESS RESULTS • Zinip-poisoning from galvanised iron piping may cause lameness and unthriftiness in pigs, but it has not been proved, yet whetner suifioient zinc coiitaminates milk oarried through the pipes to materially affect the piga. . • .Experiments have been Carried out at the. Wallaceville laboratory to determino thie point, and results of theearly tests have been reported upon by Messrs.- E. E. B. Grimmett, iL. G. Mclntosh, and E. M. Wall and Dr. C. S. M. Hopkirk in the current dssae Of" the Journal of Agriculture. Furth6r experiments are in progress. "In the New Zealand Journal of Agriculture for July, 1936," they state, ' ' dttention was drawn to the possibility that unthriftdness, arthritis and mortality in young pigs may, ih some cases, have been connected with the So'lutiOn, in the skim-milk upon which the pigs were fed, of large amount of zinc from the galvanised iron piping used for conveying the milk to the piggeries. "In view of the negative findings of Atoetican dnvestigators on the possibility of the existence of chroni.c zinc poisoning, and also doubt as to the parts played by biological f acrtors and chemical subst nces other than zinc in the causatdon of the disease, it was decided to institute experiments at the Wallaceville vetefinary laboratory. Zinq Lactate. f ' To ensure that conditions should approximate as nearly as possible to those obtaining on the farms where trouble among the pigs had been assocdated with the use of galvanised iron pipes, and at the same time obviata possible uncertainties due to insolubility of the zdnc 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. "Three young healthy weaners were seleeted from a litter of 10 young pigs. The three were fed dn a common trough witK whole-milk and, a little meal to which the zinc lactate previously dissolved in water' was added. The milk contained approximately 0.1 per cent. of zinc as lactate. . "The trial commenced on August 11 and continued untdl the last pig was killed on November 4. On about Octqber 10, 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-ofi ' their food the pigs were all noticed to be stiff ip acbion. By October 13 tKe pigs were notice.ably lame, one much more so than the, oth,er two. They also appeared to be rougher- in the coat and more flat-sided than their control littermates not receiving zinc. On October 23 it was decided to kill the pig showfing most lameness, while a second pig died on October 24, probably due to the handliUg of the day before. The third pig, which was killed on November 4, was showing similar lameness to that of the others previously killed." Results Summarised. Summarising the results, the repprt sthtes; — "ZAnc 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 caftilage having lifted ofl a soft spongy underlydng bone. This non-specilic arthritis was the cause of the lameness, and was produced apparently by ato. upset of mineral metabolism resulting • i'rom prolonged zinc feeding. "The results of the present experiment," the writers add, "are clearly •at variance with those performed elsewhere, and on which tKe opinion has been expressed that ■ zinc, jipart from the local caustie 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 foilowing points may be considered: — " (1) In the majority of experiments where zinc has been fed to animals over long periods the zinc has beeu m the form of the oxide. Tbere is no evidence that other than a small fraction of this insoluble eompopnd when fed to animals is rendered soluble by the digestive juices and'absorbed. In the few cases where the, soluble mineral salts have been fod, it is possible that their local action on the . ab&orbing surfaCes of the ealimentary canal has tended to hinder absorption nnd to promote expulsion. Reaction to Foisons. i 1 (2) The pig may be an andmal peculiarly susceptible tp zinc poisoning. It is well known that animals vary in their reactioh to various poisons. "(3) The amounts of zinc fed have been comparatnvely large, although within the range of possibility for animals under farm conditions, as demonstrated by numerous analysis of milk which have been collected from instal'ationg where lengthy galvanised iron pipes are used, ' ' (4) The effects: — at least so far as the bone lesions are concerned — may bc principally due as snggested to an upset of mineral metabolism. "Further experiments are in progress *using half ahd quartor the 1 amount Of zinc to determine at wrhat

level demonstrable effects appear in the pigs. A xecent report indicates that uo further trouble has been experienced on the farto at Atiamuri, where the first case occurred, subseqtient to the romoval of the zinc from the pipes, although conditions are ,otherwise unaltcred."