Nothing Dies: The First Registered Contraceptive Bait for Rats, and Why That Is Both the Point and the Problem

1. Introduction: attacking the other side of the equation

A population changes by births minus deaths plus immigration. Every rodent technique this journal has covered acts on the second term, and this journal's article on counting urban rats set out the consequence: removal creates vacancy, vacancy is filled, and the population returns.

One registered product acts on the first term instead.

1.1 Why this is worth an article

Because it is the first genuinely different answer to the rodent problem in seventy years, because the evidence is mixed in interesting ways, and because the reason it is not widely used has very little to do with whether it works.

2. What the product is

The basic description.

A non-toxic liquid fertility control bait for rats, containing two chemicals, both of which impair spermatogenesis in male and reduce ovarian ovulations in female rats.¹ It limits the reproductive capacity of both male and female wild Norway and Roof rats.³

It is supplied in 400 mL plastic tanks, with a pre-bait of the same formulation available, and the instruction not to re-use empty tanks.⁵

2.1 Liquid rather than solid

Which is unusual. This journal's articles on rodent baiting have dealt with blocks, pellets and pastes, all competing against available food.

A liquid competes against available water, which in many settings is scarcer than food, and it allows a dose to be taken in small repeated amounts rather than in a single meal. Both matter for §5. The observation is ours.

It also creates handling constraints a block does not have. A liquid in a tank can freeze, spill, evaporate or spoil, which in this climate makes outdoor placement a question the sources do not address.

3. The two compounds

The actives and their concentrations.

The product has very low concentrations of both actives, VCD at 0.09 per cent and triptolide at 0.001 per cent.¹ A closely related study formulation used VCD at 0.098 per cent and triptolide at 0.0012 per cent.⁴

The combination of these two active ingredients acts synergistically to suppress reproduction in both sexes.¹

3.1 Why two compounds rather than one

Because the sexes have different reproductive machinery and one compound was not going to disable both. The pairing covers the female follicle pool and male spermatogenesis,³ and the effect is reported as synergistic.¹

It also means a population in which one sex is under-exposed retains reproductive capacity through that sex, which §5.2 argues is a real possibility.

3.2 The concentrations are the striking part

One part in a thousand and one part in a hundred thousand. This journal's article on sequence-based pesticides noted an active ingredient under one per cent as unusually dilute; this is two orders below that again for the second compound.

Which is what a compound acting on a specific tissue looks like, as against a toxicant that has to reach a lethal systemic dose. The quantity needed is set by the sensitivity of the target organ rather than by the mass of the animal.

4. What they do

The mechanism, as reported.

The two actives deplete all stages of follicles in the female and disrupt spermatogenesis in the male.³ Both are known to target and inhibit ovarian function, and triptolide additionally debilitates spermatogenesis and sperm motility.⁴

4.1 Depleting all stages of follicles

A female mammal is born with a finite follicle reserve and does not generate more. Depleting all stages is therefore not a suppression of a cycle but a reduction of the pool, which is why one compound is described as ovotoxic.⁷

4.2 Why that does not make it a sterilant

Because depletion is partial and dose-dependent at the concentrations used. The manufacturer's own material states plainly that it is not a sterilant, and that if a rat stops drinking ContraPest, over a period of time they will begin to regain their fertility.⁷

That combination, an ovotoxic mechanism producing a reversible effect, is the source of most of the confusion about this product, and the manufacturer says so.

5. Why repeated consumption is required

The pharmacology, which explains the operational demand better than anything else.

The plasma half-life of triptolide in male rats, injected intravenously at a stated dose, is 15.10 plus or minus 4.44 minutes, and given as an oral dose at the same level it is 21.70 plus or minus 3.00 minutes. Triptolide is extensively metabolized, and its oral clearance was 16 times faster in males than in females.⁵

5.1 Twenty-two minutes

A compound cleared from plasma on that timescale is not accumulating in the animal. The effect on the gonad accumulates; the compound does not.

Which is why the products are only able to work through repeated consumption.⁷ A rat that visits once has had an exposure of no consequence.

5.2 The sex difference in clearance

Sixteen times faster in males.⁵ If the male clears it that much faster, the male needs correspondingly more frequent intake to sustain an effect, which predicts that the female effect will be the more reliable of the two in the field.

That inference is ours and the sources do not draw it.

6. The palatability result

The finding that surprised us most.

The bait is described as palatable and repeatedly consumed by rats even when provided with ad libitum food and water.³

And in a controlled comparison, there was no effect of inclusion of the active ingredients in the bait formulation on bait consumption, reported at a probability value of 0.739, that is, no apparent negative effect of active ingredients on how much was taken.²

6.1 Competing against free food and water

Ad libitum chow and water throughout,¹ and the bait still taken repeatedly.³ A rodenticide block in those conditions would often be ignored entirely.

Whether that reflects the liquid format, the matrix, or something about how rats sample novel fluids, the sources do not say. It is the single most commercially important property the product has, because everything else depends on the animal drinking it.

6.2 What that test actually compared

The same bait matrix with and without the actives. A difference would have indicated that the rats could detect and avoid the compounds; no difference indicates they could not, or did not care.

7. Why that matters more than it sounds

Because bait acceptance is where most rodent programmes fail.

This journal's article on rodent behaviour documented neophobia, learned taste aversion and social transmission of avoidance, and its article on glucose aversion in cockroaches documented a population evolving away from a bait matrix within a few years.

7.1 The aversion route is partly closed here

Learned aversion requires the animal to associate the bait with an aversive consequence. A rodenticide produces illness that a survivor can associate; infertility produces no sensation at all.

There is nothing for the rat to learn, which means the principal behavioural failure mode of rodent baiting does not obviously apply. That is our argument rather than a sourced finding, and §22 records it.

7.2 The evolutionary route is not closed

Selection on susceptibility still operates, and strongly: an animal that is less affected leaves more descendants by definition. Fertility control selects for resistance to fertility control more directly than a rodenticide selects for resistance to poison.

We found no source addressing that and flag it as an open question rather than an objection.

8. The laboratory result

The cleanest efficacy evidence.

In one study, laboratory rats were provided ad libitum access to the liquid bait, along with ad libitum chow and water for 21 days, after which rats that took treatment bait were placed in breeding pairs, as were control rats that took bait without active ingredients. Rats that received treatment bait had no offspring, while 100 per cent of control rats had litters after one breeding round. Similar results of no offspring were found in further breeding pairs.¹

8.1 What the control bait establishes

Control animals took bait without active ingredients and every pair produced a litter.¹ So the bait matrix, the station, the handling and the pairing procedure are all ruled out as causes of the result.

Only the actives differ between the arms, which is what makes a small study conclusive.

8.2 The design is sound

A matched control taking the same bait without actives, free food and water throughout, and a binary outcome that cannot be argued about.

No offspring against every control pair producing a litter is about as unambiguous as a laboratory result gets.

9. The free-ranging arena study

The next step out from the cage.

Researchers offered bait ad libitum for 56 days to male and female Norway rats placed in open, indoor arenas and allowed to breed for 4 rounds, a total of 138 days. The first 3 breeding rounds of treatment-matched matings produced fewer pups in the treatment rats compared to control rats, at a probability below 0.001. In the fourth round control rats were cross-bred with treatment rats.⁴

9.1 Why the cross-breeding round matters

Pairing treated animals with untreated ones is how you separate the male effect from the female effect, which §4 says the product claims to have both of.

The abstract we read does not report that round's outcome, which is a gap in our reading rather than in the study.

9.2 The organ weight note

The same abstract mentions kidney, spleen and liver weights compared to control rats.⁴ We do not have the direction or magnitude, and §17 is where general toxicology questions belong.

10. How long the effect lasts

Duration, from manufacturer-sourced material.

Rats exposed for 50 days experienced infertility lasting up to 100 days, with reduced litter sizes in those that could still reproduce.²

10.1 The ratio is the useful part

Fifty days of exposure buying up to a hundred days of effect means the effect outlasts the exposure by roughly two to one, which is what an accumulating gonadal effect from a rapidly cleared compound should look like.

It also sets the outer limit on how long provision could lapse before the population resumes breeding, and §12 is why that matters commercially.

11. The rebound

The most important qualification in the literature, from a trial on a different species.

A short-term laboratory trial with wild-caught adult black rats found that exposure resulted in complete reproductive inhibition for at least 15 consecutive days before mating and throughout a 43-day breeding cycle. The effect persisted through a second breeding cycle, with partial suppression evident in a third cycle. However, fertility rebounded by the fourth cycle.²

11.1 Why this study is the one to read

It used wild-caught animals rather than laboratory strains, and it followed them through four breeding cycles rather than one.² Both choices make it harder for the product to look good, and both are what a sceptical reader would ask for.

11.2 The shape of that result

Complete, then complete, then partial, then gone. A decaying effect rather than a switch, which is consistent with a finite exposure being metabolised and the gonad recovering function.

11.3 Which sex was affected

The account notes that it is uncertain whether the contraceptive effect affects males or females, given that the treatment impacts both sexes.²

An experiment that exposes both sexes and observes fewer pups cannot attribute the effect, which is exactly why the cross-breeding design in §9.1 exists.

12. Reversibility as feature and burden

The same property read two ways.

The effects are reversible over time if the bait is removed, and the manufacturer states that regaining fertility won't happen overnight; it could be months before fertility returns.⁷

12.1 The contrast with the alternative

An anticoagulant is the opposite on every axis. It kills rather than suppresses, it is irreversible, and this journal's article on where the residue goes documented it accumulating in predators at concentrations above reference thresholds.

Whatever else is true of fertility control, a product with a short plasma half-life and a reversible effect does not build up through a food chain in that way.

12.2 As a safety feature

A non-target animal that takes some is not permanently harmed. Combined with the point that the relatively low dose that rats need minimizes any risk to predators or non-target species,⁷ that is a materially different risk profile from the rodenticides this journal examined, where residues accumulate in predators.

12.3 As an operational burden

The programme has no completion. A rodenticide campaign ends; a fertility programme that stops is a programme whose effect expires on the schedule in §10.

This is a subscription rather than a treatment, and the commercial model has to match that or the method fails for reasons unrelated to its biology. Our framing.

13. The species problem

The technical caveat we would most want a client to understand.

Researchers noted a large difference in triptolide concentration that induced infertility in male black versus male brown rats, and reasoned that the product might be ineffective in black rats due to their apparent insensitivity to triptolide, as over a 1000-fold greater triptolide was needed to suppress male rat fertility.¹

13.1 Which species matters here

The product is registered for Norway and roof rats,³ and the Norway rat is the one this province has. The thousandfold caveat concerns the other species.¹

So for Manitoba the sensitivity question is largely moot and the registration question in §22 is the live one.

13.2 A thousandfold

Between two species in the same genus. That is not a species difference of the kind that can be managed by adjusting a rate; it is a different problem.

It also explains why that study existed: the researchers set out to test whether a product developed against one species worked against the other, which is the right question and the kind this journal's identification articles keep arriving at.

13.3 What the study then found

It presented the bait to both sexes of wild-caught black rats, on the reasoning that both male and female black rats would visit the stations.¹ The rebound finding in §11 comes from work on this species.

14. The field figure

The number that matters commercially.

Rat populations on protein production farms decreased by an average of 46 per cent following 100 days of treatment. Trials involving laboratory and wild caught rats demonstrated a 93 to 100 per cent reduction in litter sizes compared with controls.³

A twelve-month field deployment was also conducted at two urban locations, between November 2019 and October 2020.⁸

15. What 46 per cent means

Reading the field number honestly.

Ninety-three to a hundred per cent fewer pups per litter, and forty-six per cent fewer rats after a hundred days.³ Those are different quantities and the gap between them is the whole story of fertility control.

15.1 Why the population figure is so much lower

Because reducing births does not remove the animals already present. The existing adults persist until they die of other causes, and the population declines at whatever rate that happens.

A hundred days is a fraction of a rat's potential lifespan, so a 46 per cent decline over that period reflects natural mortality acting on a population that is no longer replacing itself. That is our reading.

15.2 What would make the number grow

Time. A population not replacing itself declines at its own mortality rate, so the same programme continued for a year should show more than it does at a hundred days, provided provision does not lapse.

That is the argument for measuring this over seasons rather than visits, and it is why the twelve-month deployment in §14 is the study we would most want to read.⁸

15.3 How it compares

A successful rodenticide campaign removes a far higher proportion far faster, which is why nobody should expect this to substitute for one in an acute infestation.

The comparison that matters is not against a rodenticide's first hundred days but against what the population looks like a year later, which this journal's surveillance article argued is where culling programmes lose their gains. We have not found that comparison published.

16. The resistance argument

The case made for fertility control in the research framing.

Rodent population control is a global problem, complicated by evolved non-responsiveness to rodenticide treatment. Contraceptives could help mitigate this challenge, but questions remain about their efficacy, especially for rodenticide-resistant populations.⁸

16.1 Why this is a genuinely different lever

Rodenticide resistance is resistance to a specific biochemical interference. The animals remain ordinary rats in every other respect, including reproductively.

A population selected to survive anticoagulants has not been selected for anything relevant to follicle depletion, so the resistance that closed one door leaves this one open. That is the whole of the argument and it is a good one.

16.2 The appeal is obvious

A mechanism unrelated to vitamin K epoxide reductase is unaffected by every resistance mutation documented in this journal's anticoagulant articles. A population that cannot be poisoned can still be prevented from breeding.

16.3 The caution in the same sentence

Questions remain about their efficacy.⁸ The framing is from researchers proposing to test it rather than from anyone reporting that it is settled.

17. Non-target and toxicology questions

The criticism, which deserves airing.

A critical analysis notes that the safety data sheet for triptolide describes it as fatal if swallowed or if inhaled and suspected of damaging fertility or the unborn child, with a lowest known non-inhaled lethal dose of 2.4 milligrams per kilogram in rats and a lowest known toxic dose of 60 micrograms per kilogram in mice.⁷

The same analysis states that we do not know how many milligrams of triptolide are dissolved in a tank of the product.⁷

17.1 Why the tank quantity is the right question

A concentration is not a dose. Knowing the product is 0.001 per cent triptolide does not tell you how much sits in a 400 millilitre tank, and that is the number relevant to a spill, a child, or a dog.⁵⁷

It is also a number the arithmetic yields immediately from the two figures, which suggests the criticism is about disclosure in customer-facing material rather than about the information being unobtainable. Our reading.

17.2 How much weight to give that

The hazard statements describe the pure compound, which is standard for a safety data sheet and says nothing directly about a formulation at 0.001 per cent. A great many registered products contain actives whose neat form carries severe hazard statements.

The unanswered question is the quantity per tank, and that is a fair thing to want to know, particularly for a product placed in occupied buildings.

17.3 The second-generation concern

The same source raises products in which triptolide would be derived from plant material, so that the concentration of triptolide would be less consistent, and the dosing would be less controlled due to lack of a required bait station.⁷

That is a point about future products rather than this one, and it identifies the bait station and the manufactured consistency as the controls that make the current product's dosing knowable.

18. The mouse question

A gap with a practical consequence.

The product is not approved for use in mice, although there are studies showing that VCD and triptolide also reduce fertility in mice. One observer reasoned that considering mice are much smaller than rats, their population should have dwindled if they were eating the bait, and that they may not have been large enough to access the station.⁷

18.1 The inference and its weakness

The observer reasons from an absence: mice were present, the bait was present, mouse numbers did not fall, therefore the mice were probably not drinking it.⁷

That is an argument from a negative result, and this journal's article on detection probability spent five thousand words on why a negative needs a stated effort behind it before it supports a conclusion. The station-access explanation is plausible and it is not established.

18.2 Why this matters here

House mice are a larger share of this trade's structural rodent work than either rat species. A product registered for rats only addresses the less common problem in many Manitoba buildings.

The station access point is also a design observation worth holding: a station sized for a rat excludes a mouse, which is the same geometry argument this journal's exclusion article made about apertures.

19. The commercial obstacles

Why a working product is not in wide use.

The active ingredients are more expensive than those in popular rodenticides.⁶

And clients may be concerned about having a chemical in their buildings that reduces fertility, even though it is less dangerous to human health than rodenticide poison, which the source attributes to particular fears around fertility, or simply because this risk is less familiar to them than the risk of someone in the building accidentally consuming rat poison.⁶

19.1 Why cost is less of a barrier than it looks

The active ingredients cost more,⁶ but the actives are present at 0.09 and 0.001 per cent,¹ so the quantity of expensive material in a tank is small.

The likely cost driver is the delivery: a 400 millilitre tank that must be replenished continuously, plus the visits to do it.⁵ That is labour rather than chemistry, and §12.3 already said this is a subscription. Our reasoning.

19.2 The familiarity point is well made

A known hazard is rated lower than an unfamiliar one of equal or greater magnitude. Rat poison in a building is a risk people have lived alongside for generations; a fertility-suppressing compound is not.

This journal's articles on consumer products and on sting risk both found the same pattern, where public risk ranking tracks familiarity rather than probability.

20. The visibility problem

The obstacle we think is decisive, and it is not about the chemistry at all.

There is a delay before ContraPest causes the population to be reduced, but beyond that, it's simply less clear when a humane birth control product is working than when a poison is working. When you lay down a rodenticide, you find, or smell, dead rodents. In contrast, when you use ContraPest, it may not be clear what to look for.⁶

20.1 The delay compounds it

Even a working programme shows nothing for months, since §15.1 explains that the existing adults have to die of other causes before numbers move.

So the period during which a client is asked to keep paying with no visible result is exactly the period during which the method is doing what it is supposed to do.

20.2 This is the credence goods problem in its purest form

This journal's article on credence goods established that the customer cannot assess whether the service worked. A rodenticide at least supplies a proxy: carcasses, which are evidence of something even if not of population reduction.

Fertility control supplies nothing. The successful outcome and the complete failure look identical from the corridor.

20.3 What would fix it

Exactly what this journal's detection article prescribed: a monitoring programme with recorded effort, producing a trend that can be shown. Fertility control cannot be sold on its results because it has no visible results, so it has to be sold on measurement.

That raises the cost of delivering it above the cost of the product, and §19 already had the product costing more. Our reasoning.

21. Where we would consider it

Persistent sites, not acute infestations. A 46 per cent decline over 100 days is not an emergency response.³

Where rodenticide is unsuitable. Sites with non-target risk, or where resistance has been demonstrated.⁸

Alongside, not instead. The proposal in the literature is addition to an existing integrated programme.³

Only with monitoring attached. Section 20 makes this a condition rather than an option.

Only where provision will not lapse. Section 12.2, which is a question about the client as much as the site.

And not for mice. Not registered for them.⁷

With the cold weather question answered first. A liquid held outdoors through a prairie winter is a problem the literature does not address, and §2.1 is where we raised it.

22. Limitations and open questions

Several sources are the manufacturer or draw on it. A technical use bulletin, a conference paper by the developing company, and a tertiary encyclopaedia entry summarising company studies.²³⁵

Two sources are advocacy analysis. A forum post evaluating claims and a research organisation's landscape review, both written from an animal welfare standpoint, used for the criticisms and the commercial barriers.⁶⁷

We read abstracts and excerpts. None of the primary trials was read in full, and §9.1 and §9.2 record specific things we could not resolve as a result.⁴

The field evidence is thin. One averaged farm figure and one urban deployment whose results we do not have.³⁸ The manufacturer's claim of a number of large-scale trials showing sustained reduction is a claim we have not verified.⁵

Nothing on cold weather performance. Raised in §2.1 and §21 and unresolved. A liquid bait is a different proposition in a climate with months below freezing, and none of the sources considers it.

No Canadian registration information. We have not established whether this product is registered for use in Canada, which determines whether any of this is legally available here, and the label article in this journal explains why that is dispositive.

Nothing on cost in practice. More expensive actives is not a price, and we found no figures for the delivered cost of a programme.⁶

Sections 2.1, 5.2, 7.1, 7.2, 10.1, 12.2, 15.1, 15.2, 17.1, 18.1, 19.1 and 20 are our reasoning. The liquid bait observation, the sex-clearance inference, the aversion argument, the selection question, the exposure ratio reading, the subscription framing, the population arithmetic, the comparison point, the hazard statement assessment, the mouse relevance, the familiarity argument and the visibility analysis are ours rather than sourced positions.

23. Conclusion

Two compounds at 0.09 and 0.001 per cent in a liquid bait, depleting all stages of ovarian follicle and disrupting spermatogenesis, taken willingly alongside unlimited food with no detectable effect of the actives on consumption.¹²³ Treated rats produced no offspring where every control pair had a litter, and trials report litter size reductions of 93 to 100 per cent.¹³ That is a real result against the term in the population equation that culling cannot touch.

The qualifications are equally real. Effect is reversible and requires uninterrupted provision, because the compound clears from plasma in about twenty minutes.⁵⁷ One rat species reportedly needed over a thousandfold more of one active than another, and in that species fertility rebounded by the fourth breeding cycle.¹² And the field figure, 46 per cent over a hundred days, is a different order of number from the litter result, because preventing births does not remove the rats already there.³

What will decide whether this technology is used is none of that. It is that when a rodenticide works you find bodies, and when fertility control works nothing happens at all.⁶ A method whose success is indistinguishable from doing nothing cannot be sold on its outcome; it can only be sold on measurement, by somebody prepared to count properly and show the trend. Which is the same conclusion this journal reached about audits, about light trap catches and about detection generally, arrived at from an entirely different direction.

References

1. Laboratory Evaluation of the Effectiveness of the Fertility Control Bait ContraPest on Wild-Captured Black Rats (Rattus rattus). Research publication in a human-wildlife interactions journal. Used for the description of the product as a non-toxic liquid fertility control bait containing two chemicals, both of which impair spermatogenesis in the male and reduce ovarian ovulations in the female; for the concentrations of 4-vinylcyclohexene diepoxide at 0.09 per cent and triptolide at 0.001 per cent, described as very low, with the combination acting synergistically to suppress reproduction in both sexes; for the summary of an earlier study in which laboratory rats were provided ad libitum access to the liquid bait along with ad libitum chow and water for 21 days, after which treated rats and control rats taking bait without active ingredients were placed in breeding pairs, with rats receiving treatment bait having no offspring while 100 per cent of control rats had litters after one breeding round and similar results in further pairs; and for the reasoning that the product might be ineffective in black rats due to their apparent insensitivity to triptolide, given that over a thousandfold greater triptolide was needed to suppress male fertility in that species, and that the bait was presented to both sexes because both would visit bait stations. https://www.researchgate.net/publication/347443369_Laboratory_Evaluation_of_the_Effectiveness_of_the_Fertility_Control_Bait_ContraPest_R_on_Wild-Captured_Black_Rats_Rattus_rattus
2. ContraPest, encyclopaedia entry, together with a published figure caption from the black rat study. Tertiary source summarising company studies, cited as attributed material. Used for the report that studies conducted by the manufacturer claim prolonged consumption led to a significant decrease in rat fertility, with rats exposed for 50 days experiencing infertility lasting up to 100 days and reduced litter sizes in those that could still reproduce; for the 2020 short-term laboratory trial with wild-caught adult black rats indicating complete reproductive inhibition for at least 15 consecutive days before mating and throughout a 43-day breeding cycle, persisting through a second breeding cycle with partial suppression in a third, and fertility rebounding by the fourth cycle; for the note that it is uncertain whether the contraceptive effect affects males or females given that the treatment impacts both sexes; and for the reported comparison finding no effect of inclusion of the active ingredients on bait consumption at a probability value of 0.739. https://en.wikipedia.org/wiki/ContraPest
3. ContraPest, a New Tool for Rodent Control. Vertebrate pest conference proceedings paper by the developing company. Source with a direct commercial interest, cited as attributed material. Used for the description of the product as a liquid bait limiting the reproductive capacity of both male and female wild Norway and roof rats; for the statement that the two active ingredients deplete all stages of follicles in the female and disrupt spermatogenesis in the male; for the statement that laboratory and field studies reveal the bait is palatable and repeatedly consumed by rats even when provided with ad libitum food and water; for the reported 93 to 100 per cent reduction in litter sizes of treated rats compared with controls in studies involving laboratory and wild caught rats; for the report that the product was tested on free-ranging rat populations in agricultural and urban settings, with populations on protein production farms decreasing by an average of 46 per cent following 100 days of treatment; and for the authors' position that adding fertility management to an integrated pest management programme would enhance long-term rodent population control. https://escholarship.org/content/qt5n19n3sr/qt5n19n3sr_noSplash_e15329b14e234ae948c3835a0877cfc8.pdf
4. Reduced Fecundity in Free-Ranging Norway Rats After Baiting with a Liquid Fertility Control Bait. Research publication in a human-wildlife interactions journal. Used for the framing that fertility control is emerging as a method of long-term population management and that vinylcyclohexene diepoxide and triptolide are known to target and inhibit ovarian function, with triptolide additionally debilitating spermatogenesis and sperm motility; for the study design in which liquid bait containing no active ingredients or containing the two actives at 0.098 and 0.0012 per cent was offered ad libitum for 56 days to male and female Norway rats in open indoor arenas and allowed to breed for four rounds totalling 138 days; for the result that the first three breeding rounds of treatment-matched matings produced fewer pups in treatment rats than control rats at a probability below 0.001, with control rats cross-bred with treatment rats in the fourth round; and for the reference to kidney, spleen and liver weights compared with control rats. https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1694&context=hwi
5. ContraPest Technical Use Bulletin. Manufacturer technical documentation. Source with a direct commercial interest, cited as attributed material. Used for the statement that the product is the first regulator-registered contraceptive bait, designed to lower birth rates of Norway rats; for the pharmacokinetic figures that the plasma half-life of triptolide in male rats injected intravenously at 0.6 milligrams per kilogram is 15.10 plus or minus 4.44 minutes, that the oral half-life at the same dose is 21.70 plus or minus 3.00 minutes, that oral clearance was 16 times faster in males than in females, and that triptolide is extensively metabolised; for the product presentation in 400 millilitre plastic tanks with a pre-bait of the same formulation and the instruction not to re-use empty tanks; and for the claim that a number of large-scale field trials demonstrate that the product deployed within existing integrated pest management programmes provides significant and sustained reduction in rat populations. https://docs.diypestcontrol.com/SPEC/technical-bulletin/ContraPest_Technical_Use_Bulletin_09.01.23.pdf
6. The rodent birth control landscape. Research organisation review. Advocacy source written from an animal welfare standpoint, cited as attributed material. Used for the statements that the active ingredients, and especially triptolide, are more expensive than those in popular rodenticides; that potential consumers and pest management clients may be concerned about having a chemical in their buildings that reduces fertility even though it is less dangerous to human health than rodenticide poison, attributed to particular fears around fertility or to the risk being less familiar than that of someone accidentally consuming rat poison; and that there is a delay before the product causes population reduction and that beyond that it is simply less clear when a humane birth control product is working than when a poison is working, since laying down a rodenticide produces dead rodents that can be found or smelled while with this product it may not be clear what to look for. https://rethinkpriorities.org/research-area/the-rodent-birth-control-landscape/
7. Evaluating claims about ContraPest. Forum analysis. Advocacy source with a critical standpoint, cited as attributed material. Used for the statements that the products are only able to work through repeated consumption and that their effects are reversible over time if the bait is removed, with the manufacturer's position that the relatively low dose rats need minimises risk to predators or non-target species; for the manufacturer's statement that the product is not a sterilant, that a rat which stops drinking it will begin to regain fertility over a period that could be months, and that one active is considered an ovotoxic product so that confusion about sterilisation is understandable; for the safety data sheet hazard statements for triptolide that it is fatal if swallowed or inhaled and suspected of damaging fertility or the unborn child, together with the reported lowest known non-inhaled lethal dose of 2.4 milligrams per kilogram in rats, lowest known toxic doses of 60 micrograms per kilogram in mice and 1.2 milligrams per kilogram in rats, and a median lethal dose by intraperitoneal injection of 900 micrograms per kilogram in mice; for the statement that it is not known how many milligrams of triptolide are dissolved in a tank of the product; for the concern that in possible future products using plant-derived triptolide the concentration would be less consistent and dosing less controlled due to lack of a required bait station; and for the note that the product is not approved for use in mice although studies show both actives reduce fertility in mice, with the observation that mouse populations should have dwindled if they were eating the bait and that they may not have been large enough to access the station. https://forum.effectivealtruism.org/posts/85gP3mxnpDuqKgSfk/evaluating-claims-about-contrapest
8. Field deployment study of a fertility control product in an urban setting, research publication record. Used for the framing that rodent population control is a global problem complicated by evolved non-responsiveness to rodenticide treatment, that contraceptives could help mitigate this challenge but that questions remain about their efficacy especially for rodenticide-resistant populations; for the identification of the product by its registration number and its two active ingredients as known to control rodent fertility under laboratory conditions; and for the report of a twelve-month application at two locations in an urban area between November 2019 and October 2020. https://www.researchgate.net/publication/323846449_Evaluation_of_ContraPest_fertility_control_on_black_rats_Laboratory_Evaluation_of_the_Effectiveness_of_the_Fertility_Control_Bait_ContraPest_R_on_Wild-captured_Black_Rats_Rattus_rattus