CASE NOTES
Lead poisoning in steers
Ian Poe, BVSc MANZCVS, District Veterinarian Kempsey, North Coast Local Land Services
Posted Flock and Herd September 2024
Introduction
Lead toxicity is important both as a cause of illness and mortality in livestock as well as a potential residue risk.
Case report
On 24 October 2017 a producer contacted the District Veterinarian following the death of one steer three days earlier and a second animal showing signs of blindness. At the time of the property visit the deceased animal had been buried. The sick steer was blind, with absent menace reflex and the owners reported it was walking into fences. Blood lead levels from this steer were 5.32µmol/L, confirming lead toxicity. Several old batteries were located around the shed where the cattle had been grazing.
This steer was one of a mob of 14 that had been grazing around a shed. Twelve of the 14 had been sold through local saleyards on 20 October 2017. The location of these 12 animals was determined using the NLIS database, with the 12 animals now residing on six different properties. Lead testing was undertaken on these animals. Of the 12 animals tested one had elevated blood lead levels at 0.33µmol/L. A second animal died before a blood sample was collected. A necropsy was conducted on this animal. Lead fragments were found in the reticulum (Image 1) and histopathology of the brain revealed marked multifocal to coalescing encephalomalacia of the cerebral cortex. Kidney lead levels were elevated at 85.5µmol/kg wet weight, with normal being <2.0µmol/kg. Interestingly, it had been 14 days between removal from the original property, and hence the lead source, and the death in this animal. This steer had been confined to yards during this period and fed silage.
Image 1: Lead Fragments from reticulum
The original owner purchased the steer, with elevated lead levels, back and it was returned to the property of origin under permit. The owner of the steer that died was reimbursed.
The initial clinically affected animal and the steer that was returned to the property were detained under the Biosecurity Act 2015 according to the procedure 'Lead affected food producing animal in NSW'.
Testing was undertaken in November 2018 of the two detained steers. The steer with an initial blood lead level of 0.33µmol/L returned a blood lead level of <0.10µmol/L and was released from detention. The steer that was originally clinically affected returned a blood lead level of 2.10µmol/L. Further testing over the subsequent years has been undertaken and these results are detailed in the table below.
| Blood Lead Levels of Clinically Affected Steer | |
|---|---|
| Date sampled | Blood Lead (µmol/L) |
| 24/10/2017 | 5.32 |
| 14/11/2018 | 2.10 |
| 28/2/2020 | 1.00 |
| 21/9/2020 | 1.09 |
| 31/1/2022 | 0.62 |
| 6/2/2023 | 0.43 |
| 6/3/2024 | 0.30 |
Discussion
This case highlights some important factors to be considered in cases of lead toxicity. Lead levels may remain above acceptable levels for many years following access and owners should be advised of this potential outcome at the time of diagnosis. Mortalities may be seen after removal from the lead source. This finding has been reported previously by Braddon where an animal died suddenly 10 days after removal from a lead source. It may be that under certain conditions in the rumen/reticulum lead absorption is increased, leading to an 'acute' toxicity.
References
- Braddon, E (2007) Lead Poisoning Flock and Herd case notes www.flockandherd.net.au (accessed 19 April 2024)