Lead as a nutritional hazard to farm livestock: V. The Toxicity of Lead to Cattle and Sheep and an Evaluation of the Lead Hazard under Farm Conditions

Abstract

Experiments in which the lethal dose of lead for calves and sheep was investigated using various compounds, showed that in the case of young calves 0·2 to 0·4 g. Pb. per kg. of body weight was sufficient to cause death in a few days. The fatal dose for older cattle and mature sheep was larger. The symptoms of acute lead poisoning in cattle and sheep are described. Field cases of acute poisoning-are enumerated, and it is suggested that large numbers of calves die annually throughout the country as the result of the ingestion of toxic quantities of lead. Lead paint and painters' materials were the most frequent cause of death, but cases also occurred through contamination of feeding stuffs. It has been shown by experiments on continued daily ingestion of lead that the very substantial dose of 8 mg. per kg. body weight may be tolerated for many months, and that a level of 6 mg. per kg. of body weight per day may be tolerated for even three years. On the basis of a single experiment it is suggested, that much smaller amounts of lead, 1 mg. per kg. per day, are sufficient to cause abortion in the ewe if ingested during pregnancy by animals in poor condition. Pasture levels of lead are discussed, and it is shown that, the ingestion of herbage contaminated with plumbiferous soil dust in certain areas can result in the ingestion of more than 130 mg. of lead for every kg. of dry matter consumed. The average annual ingestion of lead by sheep in the plumbiferous area of Derbyshire is high, the amount being much greater in winter than in summer. Lead in this form, however, is relatively non-toxic and the lead content of the blood of sheep in this area suggests that there is no real danger of any form of plumbism. It is concluded that cumulative lead poisoning rarely, if ever, occurs in ruminants, and that in this respect ruminants differ from human beings. Diagnosis of lead poisoning of the acute type is briefly discussed, and it is emphasised that an unequivocal verdict on analytical data alone, without collateral evidence, is often difficult.