Pindone residues in rabbits

Penny Fisher

Samantha Brown

Jane Arrow

Anticoagulants

• Inhibit Vitamin-K metabolism in liver, prevent formation of blood clotting

factors

• Clotting factors become depleted in blood, coagulation cannot occur

• Haemorrhage more likely to occur following normal movement or small

injury

• First signs of poisoning within a few days - stop feeding, lethargy

• Poisoning can be treated with Vitamin K1

• Death after several days through massive (usually internal) haemorrhage

Pindone use in NZ

Possum & rat control

• 0.5 g/kg pindone pellet bait

• bait stations

• No CSL required

Rabbit control

• 0.25 g/kg pindone AgTech or RS5 pellets

• bait stations (no CSL)

• ground/aerial broadcast (CSL required)

• Liquid concentrate applied to chopped carrot

bait (target 0.17 g/kg pindone)

• ground/aerial broadcast (CSL required)

Species Oral LD50 (mg pindone / kg bodyweight)

Rabbit 13 mg/kg single dose

0.52 mg/kg / day multiple dose

Rat 280 mg/kg single dose

5 mg/kg / day multiple dose

Possum >100 mg/kg single dose

64 mg/kg / day multiple dose

Toxicity of pindone to targets

• More toxic when ingested as multiple, consecutive

exposures

Sensitivity

to pindone

Pindone for rabbit control

• Pre-feeding not essential (slow onset of poisoning)

• Bait needs to be available over consecutive days

for optimum efficacy (higher chronic toxicity)

• More expensive than 1080 bait (usually)

• Aerial application of pindone - less controversial than 1080?

- perceived lower environmental & non-target risk

….BUT very little research or monitoring of the

effects & risks of pindone (compared to 1080)

Secondary risk of pindone ?

• Anticipated increase in pindone baiting for rabbits

• Anecdotal secondary kills of hawks & gulls

• No studies of residues in poisoned rabbits or non-

target impacts

Laboratory trials: rabbits fed different lethal amounts

of pindone bait & tissues tested for residues

Field monitoring: collect rabbit carcasses after

pindone baiting and tissues tested for residues

INFORMATION GAP

Laboratory trials – pindone residues in rabbits

• Used laboratory (white) rabbits as a model for wild rabbits

• Kept in individual cages but given daily exercise sessions

on floor

• Feed pellets, lucerne hay & carrots as normal diet

• During trials, twice daily checks for signs of pindone

poisoning

• Euthanased if signs of poisoning severe

• Necropsy & tissue samples for pindone residue testing

Laboratory trials – pindone residues in rabbits

Trial 1. Chronic exposure over 7 days - offered c. 12 g of pindone pellets each day, consumption measured

- normal lab diet available

Trial 2. Acute exposure over one day - offered c. 200 g pellets over 24 hours, consumption measured

- normal lab diet available

Trial 3. High exposure over 5 days (worst case) - offered 200 g pellets each day, consumption measured

- normal pellet diet not available but hay & carrots available

Summary results, Trials 1-3

0

5

10

15

20

25

Pin

done ingeste

d (

mg/k

g)

died Trial 2

died Trial 3

died Trial 1

survived

Highest chronic (7 days) sublethal

exposure

Highest single sublethal exposure

Summary results, Trials 1-3

• Confirm greater sensitivity of rabbits to chronic ingestion of

pindone

• Existing LD50 estimates based on oral gavage likely to

overestimate actual toxicity with bait ingestion

• Individual variation in sensitivity & importance of defining

sublethal exposure limits

• Baiting operations need to account for the least sensitive

individuals

Summary results, Trials 1-3

• First signs of poisoning occurs 7 to 8 days after bait first

introduced

• Time to death average 10.37 days after bait first ingested

• Necropsy typically showed massive haemorrhage in

cardiac cavity, leg muscles or abdominal cavity

WARNING: following image may be disturbing…..

Where are the residues?

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16

Female 2 Female 3 Female 6 Male 7 Male 8 Male 9 Male 10 Male 11 Female 1 Female 4 Female 5 Male 12

Pin

done c

oncentr

atio

n in tis

sue (u

g/g

) Liver Muscle Fat

Survived

Residues overall highest in liver, but also high concentrations in fat

Are residue concentrations related to bait intake?

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18

0.00 5.00 10.00 15.00 20.00 25.00

Pin

done r

esid

ue c

oncentr

ation in t

issue (

ug/g

)

Pindone intake by rabbit (mg/kg)

Liver Muscle Fat

Yes for liver residues…..sort of for fat…and less so for muscle tissue

What residue concentrations occur in the field?

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10

20

30

40

50

60

Pin

don

e r

esid

ue c

on

cen

tration

in tis

sue

(ug/g

)

Fat

Muscle

Liver

Field samples post

pindone-baiting

Samples from lab trials 1-3

Preliminary conclusions.....

• Fat tissue can present a similar secondary hazard as liver

• Rabbits eating excessive lethal amounts of bait in pindone

field operations >> increased residue burdens in carcasses,

available to scavengers & predators

• On paper, a high theoretical secondary poisoning risk where

scavengers have chronic feeding on rabbit carcasses (full

risk assessment underway)

• Can we change baiting practices to lower lethal exposures

in rabbits & reduce available residues?