nitrate-nitrite-methemoglobinemia complex. This toxicity for cattle, sheep, and some- 
times swine, from the presence of excessive nitrates in livestock feeds is being diag- 
nosed, reported, and published with increased frequency by several State agricultural 
experiment stations. It may become a concernofmajor importance to regulatory officials 
and is deserving of all-out research efforts. 
The pesticides and feed additives which are probably, in most instances, neither 
industrial nor nonindustrial contaminants except by accident, mistake, error, or failure 
to use as directed or labeled, will be discussed by others in this symposium. Frequent 
localized losses of animals from errors are of importance to the individual owner and 
the veterinarian. They are often reported in veterinary journals. Investigations of such 
losses help contribute to the knowledge of veterinary toxicology of the respective chemi- 
cals, but are expensive to the farmer. As an example, the killing of four milk cows and 
the sickening of five others from the feed of a local reliable feed company was recently 
reported in the Journal of the American Veterinary Medical Association. The parties 
concerned agreed that the chemical and pathologic findings confirmed poisoning from the 
urea in the feed. Such types of problems will not be included in this paper, nor will 
industrial contaminants of livestock feeds, suchas ethylene dibromide and other fumigants 
that are being used on stored grains for protection from destructive agents. 
We need scientific research on the problems of tissue and milk residues; the effect 
of the chemicals in feed and the metabolites they produce on the offspring when ingested 
during stages of pregnancy and their importance as producers of duress in triggering 
disease production by known and unknown infectious agents. 
To determine a specific industrial chemical contamination of livestock feeds is 
difficult. There are many reasons for this. The toxicity, which requires a long period of 
time to produce, is oftenachronic one. The particular batch of feed or part of pasture has 
been exhausted by the time its toxicity is known. Only one species of livestock may be 
affected. Entirely different symptoms and lesions may be produced in different species 
of animals. The state of nutrition of the livestock may be an important factor in the 
severity of the toxicity. Some poisonings are characterized by the production of certain 
enzymatic changes, which give them characteristics of some nutritional deficiency or im- 
balance. A very economical, productive, or practical process or method of production 
may be involved. There are often fears and warnings about the damage of a particular 
crop, a practical economic process,ora popular product. Toxic feed from one area where 
it is grown or stored may be used by a particular livestock feed processing plant, and 
nontoxic feed from another area may be currently processed at the time the toxicity in 
livestock is exhibited. The grease or lubricant used on the processing machinery may 
be changed, There are more reasons and examples of each which could be cited. 
At this time, we know of no proved or factual industrial contamination of livestock 
feed that is causing symptoms andlesions inlivestock or poultry over any wide area or in 
numerous communities. 
The industrial chemical contaminants of livestock feeds of the past that caused sick- 
ness and death of animals over many and wide areas of the United States, include lead, 
arsenic, fluorine, nitrogentrichloride, free gossypol of cottonseed meal, trichloroethylene - 
extracted soybean meal, and chlorinated naphthalenes. The air pollutants, which have been 
the cause of most known damage to livestock through recognized production of symptoms, 
have been lead, arsenic, and fluorine (Phillips, 1956). This was not because they were 
present in the air in amounts to cause trouble in breathing, but because they accumulated 
as deposits on forage and vegetation that are later consumed by animals. However, in the 
last 20 years industry has made great progress in the removal of arsenic and lead from 
industrial stacks as a source of contamination of livestock forage by air pollution. 
Some coals contain as much as 54 p.p.m. of lead as an impurity. In the vicinity of a 
coke oven the herbage was found to contain 25 to 46 p.p.m. of lead, which was sufficient 
to cause poisoning of cattle and sheep (Phillips, 1956). Dusts and sprays from smelters, 
where ores are smelted to obtainmetalsareother sources of a contemination of livestock 
feeds. 
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