Lead toxicity has been a health concern for many years. Over time, common sources of lead have changed, however the potential for toxicity has never resolved. A wide range of lead containing products are still accessible today. Paints, oils, lubricants, shingles, industrial contaminants, toys and batteries are all sources of lead. The amount your animal is exposed to will vary greatly depending on the source and the amount ingested. Once lead is ingested it is rapidly distributed to two main organs, the liver and the kidney, where it is stored and accumulates.
Lead poisoning affects several different organs to varying degrees. Of the organ systems, the three most apparent systems affected include the digestive and nervous system, as well as the hemopoetic (blood) system. Of these three systems the nervous and hemopoetic systems are the most severely affected. Intracranial swelling causes damage to the brain. This leads to many of the neurological signs associated with lead poisoning, for example blindness. Red blood cells are the primary blood cell to be affected by lead. These cells become fragile and rupture, resulting in an anemic state. There is also a reduced amount of iron within the cell which reduces the red blood cells ability to carry oxygen throughout the body.
Lead is an irritant to the digestive tract causes inflammation within the stomach and intestines. This may lead to varying degrees of constipation or diarrhea in many animals, however in cattle, the majority will experience rumen standstill.
Degeneration of the liver and kidneys and osteoporosis are other consequences of lead poisoning.
In cattle, there are two ‘forms’ of lead poisoning, acute and subacute, which vary based on the duration of affect. Acute lead poisoning is of short duration with only a few animals found dead. The classic behavior associated with acute lead poisoning is head pressing. Many animals will walk into an object while pressing their head against it. Other signs to observe for include, staggering, muscle tremors, blindness, intermittent convulsions, frothing at the mouth, abdominal pain/rumen standstill, and abnormal eructations (burping). Signs associated with the subactue form may be more subtle and have a greater degree of variation depending on severity and duration of lead poisoning. Signs to note include head pressing and dullness, abnormal gait (staggering or immobile), muscle tremors, blindness, head bobbing, hypersalivation, teeth grinding, rumen stasis, anorexia and diarrhea or constipation.
Although lead poisoning is most commonly seen in cattle, other species such as pigs, sheep, horses and dogs may also become affected. The most common form in sheep is the subacute form as seen in cattle. Horse will show signs of colic, pharyngeal paralysis and roaring, with difficulty breathing and potential for aspiration pneumonia. Dogs will experience hyperexcitability and convulsions as well as vomiting, anorexia, and an unusually hysterical bark. Compared to these species, the pig exhibits few neurological signs. Vomiting due to gastrointestinal irritation is the most common symptom seen in pigs.
Lead diagnosis can easily be made following the collection and analysis of several tissue samples. Blood, rumen content and feces are good samples to analyze for lead toxicity in patients who are still alive. During a post mortem, if the veterinarian is suspicious of lead toxicisty, several tissue samples may be collected and sent for analysis.
Treatment of lead toxicosis involves chelation therapy with supplementation and supportive therapy. Treatment of food producing animals is controversial and generally not recommended due to food safety concerns surrounding lead residues. Breeding animals may experience persistent reproductive problems even following successful treatment. It is not recommended for neonatal and young animals to have access to milk from affected animals as lead may be passed through the milk resulting in accumulate in the young.
Although many people believe their pastures and households are free of lead containing products, the reality is that lead toxicity still occurs today. Although treatment is possible the prognosis for animals with lead toxicity remains poor.
Should you have questions or concerns regarding your animal’s heath, please call us at Twin Valley Veterinary Health Services at 306-745-6642.
Sabrina de Baat
WCVM Class of 2015