Lethal Nicotine Intoxication in a Group of Mules

Abstract

Tobacco plants (Nicotiana spp.) are uncommon causes of poisoning in horses and mules. Most intoxications involving livestock result from the ingestion of limited quantities during gestation, causing teratogenic effects or congenital limb defects. A recent report documented Nicotiana glauca (tree tobacco) toxicity in a group of cattle, causing death and clinical signs of ataxia, depression, colic, and, in other animals of the herd, anorexia. However, although N. glauca contains nicotine, the primary toxic alkaloid is anabasine. In another report involving the review of 200 cases of unexpected death in horses and ponies, the death of 1 horse was attributed to nicotine toxicity. Other experimental work with N. trigonophylla demonstrated its toxicity to cattle, sheep, and horses, with clinical signs that included agitation, ataxia, prostration, muscle trembling, and a weak pulse. These clinical signs appeared very soon after feeding and continued for a considerable period. The following description is of an unusual case where hay fed to mules was contaminated with nicotine from the drippings of tobacco plants previously hung over the hay. Six mules from a single farm died during a 24-hour period. Five of the mules were found dead, and the sixth had signs of ataxia and tremors before death. All 6 mules were reported to have had no clinical signs the evening before. The mules were used for plowing, pulling, etc., but had not been worked for at least 1 week. They were housed in a barn and had free access to water and hay and received a corn supplement. The mules also had access to a small pasture, but examination by the veterinarian indicated no potentially toxic indigenous plants or debris. The barn in which the mules were housed was also used to hang tobacco (N. tobacum ) leaves for drying. However, at the time of the mules’ deaths, there were no hanging leaves or tobacco remnants in the area where the mules were confined. Two of the dead mules were submitted to the veterinary diagnostic laboratory. Both mules were in good physical condition and had similar gross lesions. The lungs were severely edematous and on cut surface oozed a blood-tinged fluid. The pericardial sac contained about 20 ml of a clear, bloodtinged fluid. The stomach was distended and contained a watery, primarily hay, digesta, which had a strong tobacco odor. The liver and kidneys were slightly pale. Tissue sections of kidney, liver, lung, myocardium, esophagus, stomach, brain, adrenal gland, pituitary gland, thyroid gland, spleen, pancreas, bladder wall, skeletal muscle, and sciatic nerve were fixed in 10% buffered formalin for microscopic examination. Samples of stomach contents, liver, kidney, brain, abdominal fat, urine, and vitreous were saved for toxicological assays. Vitreous was also saved for clinical chemistry