Botulism Toxicosis of Cattle

Abstract

Botulism in cattle is occurring with greater frequency in North America, coincident with increased frequency of large plastic bags used to store forage and with the increased use of small grain (ryelage) haylage. The clinical signs of botulism in cattle are very characteristic, almost pathognomonic if epidemiological factors are considered. Nearly always multiple cattle in a herd, within a few days of each other, have clinical signs of progressive muscular weakness leading to recumbency over a 2-5 day period of time. Perhaps the most dramatic, characteristic, clinical sign is the loss of normal lingual tone, to the point that the tongue will hang out of the side of the mouth. However, in order to elicit this finding, the tongue needs to be grasped manually and then pulled out of the side of the mouth with the jaws closed. In normal cattle, the tongue will then be retracted back into the mouth. Abnormal tongue tone, as occurs with botulism, will be manifest by both loss of normal muscular tongue tone and lack of prompt response to retract the tongue into the mouth. A limp tongue is clearly abnormal and with loss of ability to swallow, suggests botulism. Types A, Band type C botulism occur in cattle in the USA, but type B predominates. Type B is associated with feeding improperly fermented forage where the pH has not reached 4.5 or lower. Acid pH inhibits sporulation preventing botulinum toxin from being produced. Type C botulism occurs with the accidental feeding of carrion (birds, cat or dog carcasses) in the ration to cattle. Definitive diagnosis is challenging, often requiring multiple samples of forage, rumen contents, and/or fecal samples to be tested for botulinum spores and toxin in a laboratory experienced in botulinum testing.