Arsenic toxicity is known to cause death in stock. Common routes of poisoning include stock having access to old arsenic dip sites, where soil may be contaminated; old discarded products in farm rubbish tips, and forgotten products in farm sheds. Bushfire can increase access to chemical contaminates by stock due to the loss of, and damage to, fencing as well as the fact that burnt materials can be easier for stock to consume. Treated timber posts may contain copper chrome arsenate (CCA). CCA is a water-borne solution of up to 25% copper, up to 45% chromium and up to 37% arsenic. This treatment makes the timber highly resistant to pests and fungi, but also highly toxic when burnt.
The Dunn's Road fire started in a pine plantation on 28 December 2019 and burnt through the property in question two days later. The producer was called a few days later and reported that there were no immediate livestock welfare issues due to the fire. Two days later information came to light that the producer had some dying cattle. The producer was contacted again, and he indicated that he required some assistance for the assessment of the stock. The producer believed that the losses were the direct effects of the fire but was still uncertain as to why as there was no visual evidence of burnt animals.
On the 6 January 2020 a visit to the property was undertaken. At this stage approximately 25 head of nine-month-old weaner Angus heifers and steers had died or been destroyed by the producer out of a mob of 92.
The property had been an old apple orchard that had been cleared approximately four years ago. The trees had been pushed into big heaps and the remains of the heaps had burnt in the fire. The producer said that the fire had burnt slowly, and that the cattle had found refuge in green areas and bare ground. The producer mentioned that the smoke had been very dense at the time of the fire and was concerned that the cattle may have been dying from excessive smoke inhalation.
Initial examination was conducted on the 25 animals that had been dragged over to a dead pit. Clinical examination indicated some animals with singed hair but no extensive burns.
The rest of the mob were examined. There were up to 10 animals showing lethargy and depression. One animal was slightly ataxic in the front limbs (Video 1). Six of the animals were destroyed that day with the others to be re-assessed the following day.
An initial post-mortem of a recently deceased steer found nothing abnormal except paler than normal lungs. Initial differentials included smoke inhalation causing respiratory issues. The fact that the property was an old apple orchard was of concern due to the possibility of chemical residue. Arsenic was discussed but the producer thought that what had burnt were hardwood posts, and the pile of arsenic-treated pine posts remained intact. At this point the piles of ash were not closely examined. Fresh samples were taken from the steer for lead and arsenic testing as well as fixed samples of liver, kidneys and brain.
Arsenic was found in the liver with levels recorded of 11.8mg/kg wet weight. Lead levels were within normal range.
Histological results indicated damage to the liver and kidneys. The liver had periacinar necrosis with the kidneys having tubular degeneration and necrosis.
The producer continued to have to destroy a few animals over the next two days. By this stage arsenic poisoning from treated posts was strongly suspected. Closer examination of the ash, originally assumed to be hardwood, showed a distinct blue-green colouring. The colour was suspected to be from the copper in the CCA. The colour became even more distinct after some rain in places where the ash had been spread out by the stock.
One or two animals showed lethargy and ataxia, similar to what had been observed two days prior. A few animals that had looked ill a few days ago had started to recover.
Post-mortem findings on a recently destroyed animal showed an irritated and oedematous abomasum and haemorrhage at the pyloric inlet. Mesenteric lymph nodes appeared to be enlarged and the liver was slightly enlarged.
Liver was also positive for arsenic with levels of 12.3mg/kg wet weight.
Histological examination as presented by EMAI:
Lung: Pneumonia, bronchointerstitial and alveolar, suppurative, acute, multifocal, moderate.
Liver: Cholangiohepatitis, necro-suppurative, acute, multifocal, moderate.
Lymph node: Lymphadenitis, neutrophilic, acute, multifocal, marked.
Abomasum: Abomasitis, eosinophilic, subacute, multifocal.
The high arsenic levels in the two animals tested plus histological evidence of toxicity in animal one confirmed arsenic toxicity, the most likely source being the cattle consuming ash. The histological changes seen in the second animal post-mortem are suggestive of an infection. The lab suggested that the arsenic damage to the gut predisposed the animal to infection.
In all, 43 of the original 92 head of cattle died. Seven out of eight animals that showed clinical signs of arsenic toxicity recovered. Advice was given to the producer to withhold the animals from slaughter for 72 days.
Further investigation by the producer suggested that some of the hardwood posts had also been treated with CCA.
The disease investigation was undertaken by Local Land Services as part of Agriculture and Animal Services Functional Area (AASFA) bush fire response for animal welfare and livestock fire assessment. Prior history and discussion with the owner gave a perceived expectation that the losses were attributable to direct effects of fire. This initial assumption that the animals may have died from smoke inhalation biased the differential diagnosis in the initial post-mortem. But as animals continued to show signs of ataxia and lethargy and more required euthanasia, differentials widened to include residues, including CCA-treated timber post ash.
CCA-treated posts have been used widely across the agriculture industry and CCA is still used in timber intended for outdoor uses such as telegraph poles, fencing and landscaping. In apple orchards, CCA posts are used to hold up hail netting. New restrictions for use of CCA from the AVPMA came into place in July 2012 restricting use in high-contact timber (eg children's play equipment).
Ash from CCA-treated timber may contain more than 10 percent of its weight as heavy metal residue and swallowing only a few grams of this material can be harmful. Add to the fact that cattle seem to like to consume ash made this situation deadly for the stock. It is important to ensure that the full range of differentials are explored in emergency responses, especially where ongoing exposure to hazards is likely.
During bushfires damage to infrastructure such as fences can increase the risk of stock gaining access to potentially contaminated sites. There is also an increased risk of the availability of toxins such as arsenic in ash from CCA-treated posts. Fencing of areas that could contain chemical residues or other hazards is important after a bush fire has burnt through a property.
In this case, the contaminated area was marked off and the owner advised to work with the appropriate authorises to resolve the risk from the contaminated area.
This situation also demonstrates the importance of hazard identification when returning land previously used for another purpose back to grazing. It is vital to identify potential risks to animal health and food safety and put plans in place to mitigate these risks.
Elizabeth Macarthur Agricultural Institute (EMAI): Further tissue examinations.