Experimental lead toxicosis in ponies: comparison of the effects of smelter effluent-contaminated hay and lead acetate.

This research article analyzes the health effects on ponies who are either fed hay harvested from an area contaminated by smelter effluent, leading to high concentrations of lead (Pb) and cadmium (Cd), or given a daily dose of lead acetate alongside non-contaminated hay. A comparison of the two different exposure methods indicate similar toxicological signs and changes in blood markers, however, the severity was noticeably greater in ponies consuming the contaminated hay, as shown by the shorter timeframe between onset of effects and death.

Research Methodology

• The research experiment involved two groups of ponies: one fed with hay harvested from the Coeur d’Alene River Basin in northern Idaho which is known to be contaminated by smelter effluent, and the other group fed non-contaminated hay and given a daily dose of lead acetate.
• The hay from the contaminated site contained 423 +/- 82 mg/kg of lead (Pb) and 10.8 +/- 1.4 mg/kg of cadmium (Cd).
• The group of ponies that consumed the contaminated hay thus received daily exposures of about 7.4 mg of lead/kg body weight and 0.19 mg of cadmium/kg body weight.

Key Results

• Both groups of ponies showed similar signs of toxicity such as incoordination, labial paresis (weakness), pharyngeal paresis (weakness of the throat), CNS (central nervous system) depression, anorexia, and weight loss.
• Both groups also presented some level of anemia, often accompanied by the appearance of nucleated red blood cells and Howell-Jolly bodies in their blood—both symptoms of severe body stress or disease.
• Regardless of the method of lead exposure, once clinical signs of toxicity were observed, the blood lead concentrations was recorded as greater than 0.35 micrograms/ml for both groups.
• The research found that the concentrations of lead and cadmium in various organs (liver, kidney, spleen, brain, and bone) of the ponies were increased significantly whenever the ponies either fed on the contaminated hay or were given lead acetate.

Conclusions

• Though both groups exhibited similar symptoms, the disease process was advanced more rapidly in the ponies fed lead- and cadmium-contaminated hay compared to those given the lead acetate dose alongside uncontaminated hay.
• Neither the changes in blood composition nor the blood lead concentrations are conclusive indicators of the severity of poisoning. Hence, simple blood testing may not accurately reflect the toxicity levels in the ponies.
• The research concludes with a discussion on the potential effects of exposure to multiple heavy metals and how this might have influenced the results of the study, particularly the greater severity of symptoms noted in the group eating contaminated hay.