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a detailed field investigation to identify, remove and/or restrict access to source(s) of toxicants.
Samples for toxicology fall into three general categories (see Table 2.2):Environmental (e.g. pasture samples, weeds, feed and feed supplements, water, soil, pesticide containers).Antemortem (e.g. whole blood, serum, urine, hair).Postmortem (e.g. stomach contents, liver, kidney, perirenal fat, brain).TABLE 2.2. Samples for toxicology: guide to collection and analysis.Sample Type Amount Condition Potential Analyses EnvironmentalHay, grain, concentrate feeds, mineral supplements500 g to 1 kg compositeIn paper or plastic bags, glass jars; avoid spoilage during shippingPesticides (insecticides, rodenticides, herbicides), heavy metals, salts, feed additives, antibiotics, ionophores, mycotoxins, nitrates, sulfate, cyanide, plant toxins, cantharidin, botulinum toxin, vitaminsPlantsEntire plantPress and dry or refrigerate or freezeIdentification, alkaloids, tannins, grayanotoxins (rhododendron), cardiac glycosides (oleander, foxglove, adonis)MushroomWholeKeep cool and dry in paper bagIdentification; chemical test for amanitinsWater1 LPreserving jarPesticides, salts, heavy metals, microcystins, anatoxin‐a, sulfate, nitrate, pH. For blue green algae identification mix water:10% neutral buffered formalin (50:50) to preserve the cellsSource/bait; soil500 g to 1 kgFreeze in bag or glass jarInclude package label; variety of toxicantsAntemortemWhole blood*5–10 mLEDTA anticoagulantCholinesterase activity, lead, selenium, arsenic, mercury, cyanide, some organic chemicals, anticoagulant rodenticidesSerum*5–10 mLSpin and remove clot; special tube for zincCopper, zinc (no rubber contact if testing for zinc), iron, magnesium, calcium, sodium, potassium, drugs, alkaloids, oleandrin, vitamins, anticoagulant rodenticidesUrine*50 mLSend in plastic, screw‐cap vialIllicit drugs, some metals (arsenic, mercury), alkaloids, cantharidin (blister beetle), fluoride, paraquat, oleandrinFeces (collect at different time points)100 g plusFreezePlant identification (if not too macerated), seed identification, cardiac glycosides (oleander, foxglove, adonis), grayanotoxins (rhododendron), alkaloids (yews, poison hemlock), tannins, pesticides, illicit drugs, cyanide, ammonia, cantharidin (blister beetle), 4‐aminopyridine (Avitrol®), petroleum hydrocarbons, antifreeze, heavy metals, ionophores, algal toxinsBiopsy specimensE.g., liver, fatFreezeMetals, pyrrolizidine alkaloids (histopathology), potentially other toxicants depending on size of the sampleHair10 gTie mane/tail hair so origin and base are evidentPesticides, some heavy metalsPostmortemIngesta (collect stomach, small intestine and large intestine contents; keep separate)500 gFreeze, collect separate samples from stomach, small and large intestinePlant identification (if not too macerated), seed identification, cardiac glycosides (oleander, foxglove, adonis), grayanotoxins (rhododendron), alkaloids (yews or poison hemlock), tannins, pesticides, drugs, cyanide, ammonia, cantharidin (blister beetle), Avitrol®, petroleum hydrocarbons, antifreeze, heavy metals, ionophores, algal toxinsLiver100 gFreeze†Heavy metals, pesticides, some plant toxins, some pharmaceutical or illicit drugs, vitaminsKidney (cortex)100 gFreeze†Heavy metals, calcium, some plant toxins, ethylene glycolBrainHalf of brainFreeze†; sagittal section (leave midline in formalin for pathologist; unfrozen for AchE)AchE activity, sodium, organochlorine insecticides; yellow star thistle (histopathology), bromethalinFat100 gFreeze†; smaller OK for biopsy samplesOrganochlorine insecticides, PCBsOcular fluidOne eyeFreeze†Potassium, ammonia, magnesium, nitrateInjection site100 gFreeze†Injectable drugs; malicious injectable toxicantsMiscellaneous100 gSpecial tests, usually freeze†Special tests, e.g., spleen (barbiturates), lung (paraquat)* If possible, whole blood, serum and urine should also be collected during a postmortem examination.† Frozen is best for toxicology samples, but refrigerated is best for bacterial cultures.
See individual toxicant topics.
There are relatively few toxicants most likely to poison horses for which specific antidotes exist.
In most suspected intoxications, the best approach to decontamination is administration of an adsorbent such as activated charcoal (AC):Early and appropriate decontamination and vigorous symptomatic and supportive care often result in recovery.Always observe appropriate precautions during decontamination procedures to avoid self‐exposure or exposure of others to the toxicant.Often, mineral oil is given after suspected exposure to a toxicant. This practice should be discouraged because there is no evidence that mineral oil is an effective adsorbent for most toxicants. Mineral oil should not be administered with AC because of a possible diminution of the adsorptive capacity of the administered AC.
If the specific toxicant is known, make sure to verify what additional treatment options (antidotes) are available.
Keep in mind that multiple toxicants might be involved particularly in malicious poisonings.
Contact a pathologist at the diagnostic laboratory in your region if you are performing the necropsy. It is preferable to get some of the animals into the diagnostic laboratory for a pathologist to examine, but if this is not possible, then discussing options with a pathologist prior to performing field necropsies is recommended.
If you suspect intoxication, contact a toxicologist prior to sample collection for guidance on appropriate samples to collect and sample storage and submission guidelines.
In the event of a reportable disease, contact the state veterinarian in your region to keep them informed and allow for timely intervention if necessary.
Keep in mind the safety of you and your client, the environment and other animals. Always wear personal protection equipment for your safety.
Carcass disposal can be an important consideration and your state veterinarian or diagnostic laboratory can provide advice.
Keep in mind infectious diseases that can mimic an intoxication. A few examples of possible infectious diseases that might cause multiple deaths in a short time‐frame are anthrax, emerging diseases to which animals are naïve, and rare bacterial and viral diseases. If anthrax is a possible differential (multiple species or large numbers of animals affected; blood from all orifices – but not always), collect an eyeball and submit to the diagnostic laboratory for stain and culture. Opening the carcass will contaminate the soil with spores that will remain infectious for decades.
See Also
Specific topics
Abbreviations
See Appendix 1 for a complete list.
Suggested Reading
1 Barr AC, Reagor JC. Toxic plants: what the horse practitioner needs to know. Vet