Studies on Urea Poisoning in Ruminants I

Abstract

Recently animal feed containing urea has come into extensive use. It has been reported, on the other hand, that so-called urea poisoning breaks out when an animal takes a large amount of urea due to an erroneous manner of feeding or by accident. Little is known, however, about the symptomatology and course of the poisoning, toxic principle, and mechanism of the toxic action of urea.
In the present experiment, urea poisoning was artificially induced in 7 goats by introducing 50 per cent urea solution into the rumen. Observations were made on them for the course of poisoning. Clinically, apathetic standing, tachypnea, trembling of the whole body, and drooping neck were recognized at the initial stage of poisoining, motor paralysis leading to recumbency was shown at the intermediate stage, and constrictive spasm and respiratory paralysis were remarkable at the final stage, which was followed by death. When such clinical changes were studied by electromyography, electric discharge of antibarotactic muscle showed damping and increase repeatedly at the initial stage of poisoning and disappeared completely at the intermediate stage, and spasmodic muscle electric discharge beginning with the pharyngo-laryngeal portion was observed at the final stage. It is assumed that this spasm is that of medulla oblongata origin which precedes respiratory paralysis.
It was also clarified that nonprotein nitrogen, such as NH₃-N and urea-N, increased, to an unusual extent. in the blood and urine at the time of poisoning. Accordingly, such substance may be the principle of intoxication.
Pathological examinations on goats which died of poisoning revealed the pictures of suffocation and edematous changes in the brain, lung, liver, kidney, and adrenal gland. In addition, a phenomenon of detoxicating nonprotein nitrogen was recognized, to a certain extent, in the liver. It was supposed that the pH value of the blood inclined to the acidic side and that a kind of alkalosis was present on this account.
Moreover, a goat seems to acquire, in general, a resistance to poisoning after it is fed on a ration containing urea. For instance, some goat survived even when it was given several times as much as the toxic dose of urea.