Poisoning in Cattle – I. When to Suspect it
Poisoning or toxicosis is a disease state that results from exposure to a poison or toxicant. The condition is one of the major causes of death in cattle and despite underreporting due to lack of proper diagnosis, several outbreaks of poisoning in cattle with heavy mortality have been reported in the recent past from different states in India. Causes of the poisonings are broadly categorized as chemical toxicants (inorganic and organic chemicals) and biological toxins (biotoxins) comprising phytotoxins (plant toxins), zootoxins (animal toxins like snake venom) and mycotoxins. Lead fluoride, arsenic, pesticides, rodenticides, weedicides, strychnine, hydrocyanide, and nitrate (plant toxins) and mycotoxins are frequently reported causes of poisoning in cattle. Accidental or inadvertent exposure of cattle to these toxicants is the principal source of poisoning, though cases of malicious poisoning are also reported.
Cattle are notoriously inquisitive and will lick or eat anything, including toxic materials accessible to them. They tend to lick freshly painted walls and empty paint containers or can swallow discarded batteries causing lead poisoning. Fatal poisoning in cattle has been reported due to ingestion of toxic Agri-chemicals, rodenticides and pesticides. Environmental pollution due to urban and industrial sources and modern agricultural practices has further contributed to rising incidences of poisoning in cattle, which are more likely to ingest toxic substance present in their surroundings owing to their inherent feeding habit. Thirsty cattle will drink anything, including potentially toxic substances like diesel oil, copper containing spray liquid or any toxic liquid material accessible to them. The scarcity of food and pica also contribute to occurrence of poisoning in grazing cattle. Careless and indiscreet use of drugs and farm-chemicals, especially the pesticides, for treatment of osteoporosis and other diseases has caused fatal toxicity in cattle. Insecticides such as tetraethyl pyrophosphate (TEEP) and Parathion are completely unsuitable for use on livestock and their use for treatment of ectoparasites or maggot wound may result in poisoning.
Many times, poisoning cases are not properly diagnosed in field conditions and may be mistaken for infectious diseases or other conditions presenting clinical signs alike poisoning. For example, cases of cyanogenic glycocide (cyanide/ hydrocyanide) poisoning have been misdiagnosed for anthrax and those of lead toxicity for trypanosomiasis and rabies or other diseases associated with signs of brain dysfunction. Accurate diagnosis of poisoning is important not only for effective treatment and patient management, but also to address veterolegal issues. The valid and final diagnosis of poisoning depends on four evidences (1) Circumstantial evidences (2) Clinical evidences (3) Pathological evidences and (4) Laboratory evidences involving systemic approach to piecing together information derived from complete case history, clinico-pathological observations, laboratory investigations including chemical analysis, and sometimes bio-testing of the suspected toxic material.
A field veterinarian is supposed to be the first professional attending the illness of animals including suspected poisoning. His primary responsibilities are to initiate the process of diagnosis of recording history and collecting samples for laboratory investigation and take decisions regarding treatment of sick animals. A complete case history is very crucial to give right direction to the diagnostic process and identifying sources of poison. Therefore, the veterinarian has to apply his professional experience and wisdom to record proper case history that will assist him making tentative diagnosis and initiate treatment without waiting for the results of laboratory investigations. The history should include important basic information about surrounding environment and chronology of events, animal management practices, epidemiologic aspects including case information (incidence rate, geographic location, affected and non-affected animals) signalment and present and past history. In case, the veterinarian is unable to make a tentative diagnosis, it is pertinent to seek expert advice. The next step for diagnostic approach is collecting samples from affected and unaffected animals and conduct post-mortem as per standard protocol and procedure. Legal aspects should be completed in veterolegal cases where malicious poisoning is suspected.
Poisoning is suspected when a number of previously healthy animals in good nutritional status suddenly become sick with the same clinical signs and necropsy findings. This situation may also arise in case of infectious and nutritional deficiency diseases. Retrospective disease data and knowledge of local environmental factors such as the presence of poisonous plants in the geographical region are useful to differentiate the cases of poisoning with those of infectious and deficiency diseases. Onset of illness in animals soon after the change in the ration or housing, or immediately after the medication, spraying or dipping and after a change of pasture or habitat usually indicates the possibility of poisoning. The presence of toxic materials or toxic wastes or poisoned baits in the proximity of animals is also important evidence for suspecting poisoning. Illness in cattle grazing in an industrial area, especially in the vicinity of newly established industry may be associated with poisoning.
Some poisoning incidences can be diagnosed accurately in the field itself by circumstantial evidences and specific clinical signs. For example, clinical signs of lameness, dental lesions, bony exostosis and other skeletal deformities in cattle in fluoride endemic areas, or in the vicinity of aluminum, ceramic, fertilizers and cement factories are clear indications of fluoride toxicity. Similarly persistent scouring, depigmentation and bespectacled appearance in calves raised near oil refineries are suggestive of copper deficiency and molybdenum toxicity. Signs of nervous disorders in cattle in the proximity of primary or secondary lead smelters should be considered as those due to acute lead poisoning.
Read: Poisoning in Cattle- II Post-mortem and Laboratory Diagnosis
Dr. Devedra Swarup
BVSc & AH, MVSC (Vet Med), PhD
Former Director, ICAR-CIRG and Head Division of Medicine and Centre for Wildlife, ICAR- IVRI