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Toxins used in the Garden from a Veterinary Perspective- the Rodenticides

By Geoff Stein (palmbobApril 9, 2008
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In our constant efforts to battle the forces of nature while attempting to create our own perfect versions of nature (our gardens), we are often 'forced' to use substances to thwart or even kill garden pests. This article discusses some of the toxins used to kill rodents, but what deadly consequences those may have on our own pets.

Gardening picture 

Fighting garden pests can be a frustrating and full time job. Such pests include insects, weeds, rodents, snails, fungus etc.  Many of the toxins we use to battle these garden pests are not only toxic to the pests, but us as well.  Fortunately we are able to read the labels and try to avoid as much contact with these toxins as much as possible.  Unfortunately we cannot explain to our pets and other ‘innocent' animals that they should avoid these toxins, and they can sometimes be the unintended victims of such poisons.  As a veterinarian, I see a lot of poisoning cases, and probably most fall into this category.  In previous articles I may have made the reader a bit complacent by trying to put some of the toxic plants in proper perspective- turns out most toxic plants are far less worrisome that we would be lead to believe.  However, toxins that we purposefully put out in the garden usually fall under the opposite category: being MORE toxic and dangerous that one would might be lead to believe, particularly to our pets.  It never ceases to amaze me how often dogs (rarely are cats ‘experimental enough' to try most toxins meant for our serious garden pests) are brought in by owners completely oblivious of the toxins they have just allowed their pets to consume.  In this article I will try to cover some of the more commonly used rodenticide toxins we use in the garden and the potential veterinary consequences of such use.  I hope someday someone will do an article on our own personal dangers with such toxins, but I suspect they are somewhat similar to what we see in our poisoned pets.

The largest pests we find ourselves battling in our gardens with toxic brews are the rodents (most larger pests (like deer) probably require something a bit less hazardous than poisons since the amount of poison needed to kill a deer would certainly be an enormous health hazard not only to you and your pets, but perhaps the entire community as well).  There are quite a number of rodenticides on the market, something that always puzzles me, as there are only a few cases of poison resistance in the rodent world.  To me dead is dead, and these ‘super-toxins' seem crazy... especially when our beloved pets gobble them up.  Rodenticides nearly always taste great to dogs (and even cats sometimes eat these) as they are supposed to taste good to rats.  So pets will often seek these poisons out, digging them up out of the soil, climbing shelves in the garage to eat them, and even climbing trees to get to the deadly stuff.  Do NOT believe the labels when they say not toxic to pets.  What they are basically claiming is that the same amount needed to kill a rat may not kill your dog which is not necessarily true in the first place (there are LOTS of dog breeds hardly bigger than rats!).  But even if it was true, most dogs do not just gobble up one morsel as a rat might, but they keep eating more and more of it until they are full.  And unfortunately most rodenticides don't start making dogs sick for many hours to days later, so there is no learning curve.  Dogs poisoned once and treated will often get a taste for these poisons and seek them out more vigorously in the future.

Image 

Dogs sniff out everything and often love the smell, and taste, of rodenticides

The anticoagulants:  Warfarin is the original anticoagulant rat poison.  It was a common rat poison at one time.  It was an easy poison to treat in a dog (if gotten to in time) and dogs would only need to be on the antidote (thank goodness this one has an antidote!) for a week.  Common names included Rodex, Blitz, Rid-a-Rat, Eagles etc.  Unfortunately this was a toxin that a few rats seemed to build up a resistance to (though not our pets of course).  So in response to this spotty resistance we created an entire new generation of super toxins designed to kill rats even deader than before (eg. brodifacoum- D-Con, Havoc, Jaguar, Warrior Chunks, Enforcer etc. ; diphacinone- Assasin, Tomcat, Ditrac, Exterminator's Choice, etc.; difethialone- Decease, Generation, Hombre ; pindone- Enforcer Rat Bait, Duocide;  and bromadialone- Hawk, Maki, Boot Hill, Just One Bite, Tomcat Ultra etc. ).  Poisoning with these newer anticoagulants requires treatment for up to a month or more until all the poison is out of the pet's system.  Yes there is an antidote (vitamin K1).  But the problem with these rat poisons is we veterinarians don't always get a good history of a pet having eaten rat bait and that can seriously delay proper treatment.  And it isn't clear why a pet is acting sick.  We cannot ask them if they ate any pretty turquoise pellets.  And if we don't figure it out in 24 hours or so, it can sometimes be too late to do anything about it. 

Image example of one product and the typical turquoise pellets

Most rat baits are a brilliant turquoise in color. Unfortunately this is not a universal truth- there are other even nastier toxins this color, and some rat baits are not turquoise.  But that is the most common case, and I see a lot of bright turquoise vomit when we see one of these dogs and I have to make them vomit up their psychedelic meals.

The symptoms we see from anticoagulant consumption include lethargy, coughing, lameness, anorexia, dizziness, seizures and sometimes bleeding externally (from nose, mouth, urine and in stools).  Unfortunately external bleeding is actually a relatively uncommon symptom though it is a good one to help guide a veterinarian in the direction of the proper diagnosis.  Another common first symptom is death with no warning.  There are tests that can be done that will quickly diagnose the likelihood of such a poisoning, but often these tests are not done either because an owner, insisting their pet could not have possibly been exposed to rat bait resists, or because the symptoms don't lead one in the direction of poisoning (I see a LOT of limping and coughing dogs and cats and rat bait poisoning is rarely high on my list of possibilities).

Once a diagnosis has been made and the pet has been started on vitamin K1 and given a blood transfusion if needed, the prognosis is good as long as treatment is started soon enough.  But treatment can involve many days in the hospital and end up costing several thousand dollars.  Or it may not even be successful.  Is it worth the risk? 

Bromethalin-  this is a newer rodenticide that sounds a lot like some of the anticoagulants, but it's not.  It is usually sold under the names Assault or Vengeance.  This is a potent neurotoxin but also commonly colored turquoise like the anticoagulants.  Dogs and cats that eat this usually don't show signs of poisoning for up to a week,  and then, if they've eaten enough (doesn't take much) they start to show symptoms of tremors, seizures, crying out, increased heart rate, depression, coma and then death.  Once symptoms start, little can be done to correct the problem, and many pets either die or may develop permanent neurological problems.  If you suspect your pet has eaten this poison, get them to vomit as soon as possible and detoxify right after.  Unlike the case with the anticoagulant poisons, there is no antidote for this poison.  I have no idea why the anticoagulants weren't good enough that something this toxic had to be developed.   Don't use this stuff!!

Zinc Phosphide- this is an inorganic toxin that is not just designed for rats, but just about any pest mammal that is unlikely to vomit it up.  Unfortunately it is also highly toxic to birds, fish and our pets as well.  It is usually hidden in a common food (apples, meat, grain etc.) and mixed with a product that causes vomiting, so if eaten by a dog or cat, it is supposed to make them vomit (rodents and rabbits, the usually target animals, cannot vomit, so they cannot rid themselves of the toxins).  But if a pet has eaten a moderately large meal, they often will not vomit this poison.  Additionally it has a garlic flavor which is supposed to be repellent to dogs and cats (garlic is often added in tiny amounts to dog food to enhance flavor, so this garlic additive does not often work to repel some dogs).  Birds have no sense of smell, so this does not deter them, either.  Fortunately this is a somewhat difficult toxin to acquire for the home gardener, so is not a poisoning I see often.  Common names for this poison include Arrex, Denkarin Grains, Gopha-Rid, Phosvin, Pollux, Ridall, Ratol, Rodenticide AG, Zinc-Tox and ZP.

Cholecalciferol- this is another rodenticide that was designed originally because it was NOT supposed to be a danger to pets.  But sadly that did not turn out to be the case.  The common names for this one include Quintox and Rampage.  This is a toxic form of vitamin D.  Ingestion of this toxin causes the body to poison itself with calcium, and it is a pretty effective toxin.  Pets that eat this product become lethargic, start to vomit and get very weak, usually about 2 days after they eat it.  Almost all the organs in the body are effected, but most toxic animals develop kidney and heart failure before other organs are effected badly enough to cause death.  If treatment is started early enough, most pets can be saved, but it is a painful treatment and there is no guarantee as to the outcome. 

Strychnine- this is an extremely toxic product usually used against rats and gophers, and historically coyotes (now illegal).  I have seen several cases of this toxicity in dogs and it is horrible- constant unending seizures.  Fortunately treated dogs can often be saved, but without treatment, the toxins are usually fatal, causing overheating or respiratory collapse and/or heart failure.  Snail bait, a completely unrelated toxin, has the exact same symptoms of constant seizures and an even more common poisoning (one of the most common toxicities seen in dogs).  This will be discussed in a future article.

ANTU is a rarely used rodent toxin that causes respiratory failure from pulmonary edema (lungs fill up with liquid causing drowning)- it is an extremely effective and difficult to treat toxicity.  It was designed to be vomited by animals that could vomit (eg. People, dogs, cats etc.) but not by rodents since they can't vomit.  Unfortunately animals with a full stomach of food already would not vomit if they then ate this toxin.  Fortunately it is now quite rare.  I have never seen a case of this poisoning.

Red Squill- this is a plant I even have growing in my garden (Urginia maritima), which fortunately is bad tasting and not a serious toxic plant threat.  However, made into a toxin, it can cause heart failure in animals that don't vomit it up.  It, too, is a rarely used toxin today.

Image my own plant in the yard- had no idea they made a rat bait from this!

There are dozens of other rodenticides that have been used over the last 50-100 years, but the ones above are the most commonly seen (though the last two are pretty rare now).  All can potentially cause death in our pets.  I certainly recommend not using these poisons if you have any pets at all.  Even if you think there is no way your pet could be exposed to these poisons, you could be wrong.  There is an amazing number of ways you could be wrong and I see them all the time- a garage door left open, a gardener taking it upon himself to do you a favor by applying the poisons, a professional exterminator misjudging the ability of a pet to seek out the toxins, a ‘secure' poison rodent trap somehow being left open, etc.  It is not worth the risk!  It may not be as effective, but I recommend getting some simple rat traps, cats, snakes, road flares etc. if you simply must do something about the rats and gophers in your garden.  And there are dozens of rat and gopher traps that are not pet hazards you can play with.  And then there is learning to live with your ‘pests' and find some happy compromise in the garden.  But killing your own pets is rarely the best way to go about fighting your rodent situation.


  About Geoff Stein  
Geoff SteinVeterinarian and Exotic Plant Lover... and obsessive, compulsive collector of all oddball tropical and desert plants.

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Discussion about this article:
SubjectTopic StarterRepliesViewsLast Post
safety for our dogs pomegranite 6 27 Feb 3, 2010 11:46 PM
Thanks! critterologist 9 56 Apr 10, 2008 6:32 AM
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