• possumWhether we like it or not, 1080 poison is widely used to kill introduced mammalian species that may threaten native wildlife and harbour TB.
  • Occasionally large pest-killing operations take place in areas not readily accessible on foot. Licensed operators drop 1080-laced bait from planes and helicopters over huge areas of forest.
  • The target animals are usually possums, rats and stoats.
  • The operators take steps to prevent other species being killed, but inevitably accidental poisoning of domestic animals (and wild deer) occurs.

This article helps explain which animals are most at risk and how concerned owners can prevent accidental poisoning.

Species susceptibility

Species vary greatly in their susceptibility to 1080.
Possums and rats are intermediate in susceptibility and birds and mice are relatively resistant, but unfortunately, as this table shows, dogs are extremely susceptible.

 

Lethal dose in mg1080/

kg body weight

 

Relative tolerance

dog = 1

Dog 0.06         1
Cat 0.4   6
Rabbit 0.4   7
 Cattle, sheep, deer  0.2-0.6    3-10
 Possum  0.7    12
 Rat  1.0    17
 Humans  2.0    40
 Mouse  13    220
Birds  3-19   50-300

 

Clinical signs

If an animal eats 1080 there is generally a latent period of at least 1½ hours before signs of poisoning develop.

  • In dogs the signs of 1080 poisoning are very distressing. The dogs show frenzied behaviour or behave as if terrified, and vomiting is common. They may continually bark and howl, become extremely agitated and eventually develop convulsions which may last for hours before they die. The dogs appear to be in great distress although some scientists argue that they may not be fully conscious throughout. Veterinary treatment at a very early stage may save a few, but usually if clinical signs develop it's too late.
  • In ruminants the signs of poisoning are not so extreme. Sheep and cattle become dull and staggery, tremble and develop convulsions before they die.
  • Horses may sweat and tremble.
  • Pigs usually lie quietly with slow laboured breathing, they develop convulsions and die.
  • Rabbits often seem normal for several hours before developing convulsions then they die within minutes.
  • Possums die from 5 to 70 hours (average around 12 hours) after eating 1080 and they may show signs of pain and disorientation before death.

Degradation of 1080

  • 1080 in bait is quickly broken down by bacteria in the soil and in water, but generally it's the amount of rain that falls that determines the time taken for uneaten baits to become harmless to stock.
  • Intermittent rainfall has a greater leaching effect than a single heavy downpour.
  • At least 10 cm of steady rain is required to leach 1080 from one inch cubes of carrot into the soil. Much more rain is needed for thicker slices.
  • Oat baits leach more readily than chopped carrot but at least 2.5 cm of steady rain is required to render the bait harmless.
  • In most environmental conditions, the 1080 disappears within several weeks.

Extended dry periods can result in dehydration and shrivelling of carrot bait but may not reduce its 1080 content, so it can remain toxic for months. The next significant rainfall may serve only to rehydrate the bait, making it palatable for stock and resulting in poisoning.

In decomposing carcases 1080 breaks down quite quickly, but in dry conditions there is a risk that poisoned carcases may dry out (mummify). Then 1080 can remain intact in the stomach for months, and could poison scavengers such as dogs.

Freezing of carcases in winter may allow 1080 to persist in carcases for weeks.

Precautions

Compound 1080 can only be used by approved operators. They know the risks and know what precautions must be taken.
The withholding period (the time that should elapse before animals are allowed onto poisoned areas) depends on the bait used and the weather conditions.
Operators usually warn animal owners to keep animals away from the poisoned area for at least 8 weeks or until at least 10 cm of rain has fallen.
They may also advise farmers to muzzle dogs working in the area.

To target pest species, the operators put the 1080 in bait such as carrots, jam or grain or they may use specially formulated 1080 pellets or paste.
Dying the bait grass-green makes it less attractive to birds but rabbits and possums are not deterred by the colour.

Accidental poisonings

Most recorded accidental poisoning cases involve dogs, reflecting the high susceptibility of dogs and the concern of their owners. Cases occur when dogs eat the poisoned bait or when they scavenge poisoned carcases. In dry conditions it is possible for 1080 and therefore the risk of accidental poisoning to persist for months.

Most accidental poisoning of livestock or pets occurs when poison is dropped outside the designated area, when animals wander onto poisoned areas, or when livestock are moved back to poisoned areas too soon.

However there are cases on record in which poisonings occurred well after the withholding period of 8 weeks. These were generally in areas that had received little or no rain since the poison operation.

  • In one incident over 100 sheep died 10 weeks after a poison drop. The weather had been dry since the drop but a recent rainfall rehydrated shrivelled carrot pieces and they became palatable.
  • A dog was poisoned 5 months after a poison drop when it ate the mummified carcase of a rabbit that still had 1080 carrots in its stomach.

Bottom line

There may be a risk of accidental poisoning of domestic animals after 1080 poisoning operations. Dogs are particularly at risk. Take note of any 1080 operations in your area and keep your animals well clear of them until at least 8 weeks have elapsed and a good deal of rain has fallen, and keep your dogs muzzled if there is any risk.

References available on request.

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