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Lead Loss from Blood and Milk and the Level of Contamination of Muscle, Liver, Kidney and Bone in Lead Exposed Cattle


<OL> <LI> This study will characterize lead contamination in animals with clinical lead poisoning and those with no clinical signs of poisoning in herds with known exposure to lead. We will determine the source of the lead and the importance of lead contamination in asymptomatic animals from such herds. We will use blood analysis and milk analysis from live animals and tissue analysis including liver, muscle, and bone from dead animals. <LI> We will determine the rate of lead elimination over time based on the decrease in blood and milk lead concentrations. Blood represents the circulating lead that is not stored in tissues. Blood is easily collected and is frequently used to monitor the level of exposure and response to treatment in animals exposed to lead. Milk is a potential route of lead excretion and preliminary results show elevated lead concentrations in milk from exposed animals. Milk is chosen for analysis because it is easily collected from most lactating cows and is a human food. Knowledge of the rate of lead loss from blood and milk will help the veterinary diagnostic community to estimate when lead exposed cattle can be safely returned to food production. <LI> We will also determine the level of lead contamination in solid animal products such as muscle and organ meat (liver and kidney) that are sources of food for humans. This information will be used to assess the safety of the meat produced and the additional economic impact of lead poisoning. Lead concentrations in bone will be determined because bone is a major storage site for lead. Lead can be released from bone over the lifetime of the animal, particularly during growth and at parturition. Small amounts of lead sometimes leach from bone during food preparation (Baxter et al. 1992) <LI> We will use field cases of lead exposure. The data generated will be immediately applicable to the control of lead poisoning and lead contamination of animals in field cases. The information accumulated will be easily applicable to future field cases of lead poisoning. <LI>We will publish our results in a peer-reviewed journal.

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Non-Technical Summary: Lead poisoning in cattle is a common problem and could cause to lead contamination milk or meat entering the human food chain. This study will determine the rate of lead loss from exposed cattle and the best way to manage exposed cattle to prevent contamination of cow milk and beef intended for human consumption. <P> Approach: 1. Six herds will be invited to participate. Participation will be anonymous. Compensation will be available to participating veterinarians. The New York Department of Agriculture and Markets will encourage participation. If we are unable to locate 2 herds within the first year, herds identified by other laboratories will be invited. 2. We estimate that 10-30 animals per herd will be sampled based on our experience with small herds of 20-80 animals and limited lead exposure within herds. a. Environmental samples will be collected to determine the source of lead. The Analytical Toxicology Laboratory at the Animal Health Diagnostic Center (AHDC) routinely processes samples for quantitative lead analysis using atomic absorption spectroscopy (AA). b. Blood and milk will be collected to determine the level of exposure of symptomatic and asymptomatic exposed cattle. Blood samples will be collected from beef calves and dams. Milk and blood will be collected from lactating cows when possible. c. Tissue samples (muscle, liver, kidney, bone) will be collected from cattle that die, are culled, or are slaughtered. We expect to collect tissues from 12 cattle and that 6 of these will transported to the AHDC for routine necropsy. 2. The rate of elimination is expected to follow first-order kinetics, (i.e., half the dose is eliminated per unit time) so the absolute amount eliminated will decrease with time. Sampling will be repeated at increasing intervals: 2 weeks (1st interval), 4 weeks (2nd interval), and 8-12 weeks (3rd interval to end) and terminated at lead concentrations of 2.5 micrograms per deciliter. a. Samples will be analyzed routinely at AHDC. b. The half-life of lead in blood will be calculated using the equation half-life = 0.693/slope. Slope is calculated from a computer-generated semilog plot of the change in concentration over time (Rumbeiha et al, 2001). c. We will determine if the equation log(y) = 3.19(x)-2.36, where y is the concentration of lead in milk and x is the concentration in blood, (Oskarsson et al. 1992) describes our findings. 3. Muscle, liver, kidney, and bone will be collected from cattle removed from the study due to death or culling. Bone will be collected from the distal physis of the femur where a change in bone density was seen in a lead poisoned calf (OConnor and Doige 1993). Adjacent gastrocnemius muscle will be collected. Lead concentrations are highest in muscle less than 10 millimeters from bone (Baxter et al., 1992). Rumen contents and abomasal contents will be collected to rule out continued exposure. Complete necropsies will be performed on carcasses that can be moved to the AHDC (est. 6). Field collection will be performed on other carcasses with samples collected for routine histopathology. Samples for lead analysis will be processed routinely at AHDC. 4. Collected data will be reported to the herd veterinarian. The source of lead will be removed from the environment of the animals as soon as possible. 5. We will publish the results of this study in the form of one or more manuscripts in peer-reviewed journals such as the Journal of Veterinary Diagnostic Investigation.

Bischoff, Karyn
Cornell University
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