“There are just three first generation active ingredients registered as rodenticides in New Zealand: diphacinone, pindone and coumatetryl,” Key Industries explains.
 

As a group, first generation active ingredients were used as rodenticides 20 years before the initial second generation anticoagulants were discovered: warfarin (1950) diphacinone (1952) pindone (1953) and coumatetralyl (1956).
 

Resistance to warfarin in rodents was discovered in 1958 and by the mid to late 1970’s the second generation anticoagulants were developed providing relief from resistance – hence their name.
 

Resistance to the other first generation anticoagulants has not occurred in NZ but today warfarin has been relegated for use as

a human pharmaceutical drug for dissolving blood clots in those suffering from thrombosis or heart disease.
 

So what exactly is a first generation anticoagulant rodenticide?
 

“This group of rodenticides is collectively known as multi-feed anticoagulant toxicants. “That is not to say that they cannot act as a single feed toxicant if enough is ingested, it just means that the lethal dose is much less when fed over several days than in one single dose, e.g. a 450 g Norway rat would need to eat 120 pindone pellets in a single feed to ingest a lethal dose whereas it would only need to eat 2.1 pellets per day (11 pellets) to acquire the same effect over five days.”
 

The same cannot be said for second generation (single feed) anticoagulants, Key Industries says.
 

“These are much more toxic than their first generation cousins.
 

“Once a rat has ingested a lethal dose, it has in effect signed its death warrant even though it may continue to feed for a few days before it dies.”
 

This means that a rat could be carrying several times the lethal dose of second generation rodenticide that is required to kill it.
 

“If the dying rat is eaten by a cat, dog or bird of prey the secondary poisoning effect can also be lethal to the farm animal if not remedied quickly by administering Vitamin K.
 

“Farm dogs can be worth several thousand dollars and a well-trained hunting dog is very hard to replace.”
 

First generation rodenticides therefore need to be administered over several days to be effective, and the bait station should not be allowed to be empty during the baiting period. Rats usually die within five to seven days after feeding starts, but it is useful to bait for longer than this because dominant alpha male rats may sometimes prevent others in the colony from feeding. Rats lower in the social hierarchy may only begin feeding when the dominant rats have died.
 

“Secondary poisoning is less likely with first generation anticoagulants because a dog or cat would have to eat a poisoned rodent

every day for several days in succession to acquire a lethal dose.
 

“This is not impossible, but much less likely to occur than if it eats just one rat that has fed for several days on a second generation poison.”
 

Dispensing rodenticides in a lockable bait station is always recommended so that children and animals cannot gain access.
 

Farm animals are more likely to be poisoned through eating unsecured bait than via secondary poisoning of eating a dying rodent, the company says.
 

Bait stations with an open entry for pelletised baits should not be used around the farm yard and always be placed at heights

where dogs and children cannot gain access.
 

For more detail contact sales@key industries. co.nz.