PPC117 | Technical

Cholecalciferol rodenticides have been on the market for some time now. However, there are significant differences between cholecalciferol-baits and anticoagulants, with which we’re probably more familiar.

We asked Richard Faulkner from Envu, the company that manufactures Harmonix Rodent Paste, and Alex Wade from BASF, the manufacturer of Selontra, to give us a back-to-basics run down of cholecalciferol safety. 

How does cholecalciferol work differently to SGARs?

AW: SGARs are also known as AVKs, or Antivitamin Ks. They work by inhibiting enzymes in the rodent’s body, which causes physiological changes due to a loss of a metabolic process downstream.

RF: The mode of action for cholecalciferol is a form of Vitamin D3. It floods the target animal's body and causes hyper-calcification (also known as hyper-vitaminosis).

Once a lethal dose is consumed, the animal is unable to process and assimilate the excess calcium, which builds around the vital organs (liver and kidneys first) and results in death.

Vitamin K1 is needed for blood clotting, so once it is depleted, the animal's blood clotting mechanism fails, which will lead to internal haemorrhaging and death.

AW: Yes, cholecalciferol works with an entirely different mode of action: it is essentially an increase of a substance, which results in too much of a metabolic process occurring in the rodent’s body.

This increase creates an excess, which causes the body to undertake processes such as the mobilisation of calcium and its subsequent calcification onto soft tissues at an increased rate and in critical locations within the rodent’s body.

What are the key environmental considerations when using a cholecalciferol rodent bait compared to an SGAR? Are there any unique risks associated with using a cholecalciferol product?

AW: Pest professionals undertaking a rodent control program should conduct a thorough Environmental Risk Assessment before deploying any lethal control measure.

RF: Cholecalciferol is classified as a sub-acute toxic rodenticide, whereas SGARs are chronic rodenticides. Sub-acute rodenticides are more acutely toxic, so there is a greater likelihood of primary poisoning when ingested directly by a target or non-target animal.

AW: One key difference between cholecalciferol and AVKs is that cholecalciferol is largely metabolised by rodents during calcification, meaning that after the process has occurred, the rodent shows significantly lower risks to non-target scavenging and predatory animals in terms of bioaccumulation.

RF: The principles for conducting an Environment Risk Assessment (ERA) for a cholecalciferol rodenticide are the same as those for conducting an ERA for an SGAR, as both are toxic substances.

First, you need to justify the use of rodenticides. This will identify the target rodent, the level of rodent activity, the risk to human health, and the risk of re-invasion. You also have the same environmental considerations: nontarget species, companion animals, livestock, water bodies, water sources, alternative food sources, proofing, etc.

The main risk associated with using cholecalciferol products (as with all rodenticides) would be that of primary poisoning. As previously mentioned, cholecalciferol is acutely toxic.

Professional pest managers must carry out a thorough Environmental Risk Assessment. They must ensure they follow all product label instructions to the letter; after all, the LABEL IS KING.

Open and thorough communication with the customer is key. If the customer has companion animals, can these be excluded from the area for the duration of treatment? For example, fencing can isolate the area and reduce risk.

When using the bait in bait stations, ensure that the bait is secured and that the bait stations are also secured. A compliance label stating that cholecalciferol is in the bait station must also be in place, and this is a legal requirement (the same for SGARs).

When burrow baiting, ensure that the bait is placed deep into the burrow, that the bait is threaded onto a wire or burrow baiting star, and that the burrow is backfilled and marked.

AW: The biggest risk is treating cholecalciferol like an AVK. Regardless, all rodent control programs require a commitment to ensuring that products are used responsibly to avoid causing exposure to non-target species.

In addition to following the label's detailed, safe handling instructions for proper and effective use, it’s important to ensure that if a risk is identified, a mitigation process is in place:

• Can I eliminate this risk?
• Can I substitute this risk for one of a lesser impact?
• Can I use control tools to separate the risk from the subjects, for example, using tethered and secure tamperresistant bait stations?
• Can I put processes in place to reduce the impacts, such as correct labelling, reporting, and communication of these risks, and having first aid guidance for physicians and vets on file as a last resort in case of emergency?

Does cholecalciferol have any unique benefits pest professionals should consider when selecting these products?

AW: Remember that cholecalciferol is not an AVK. Understanding the differences between the two unlocks a world of potential for professional pest managers to tap into when building their integrated pest management strategies.

RF: The unique benefit of cholecalciferol rodenticides is that there is no known rodent resistance, unlike the resistance exhibited by Mus musculus (House Mouse) and Rattus norvegicus (Common Rat).

Once the rodent consumes a lethal dose, the effects will quickly follow, resulting in mortality.  Also, when a target animal consumes a lethal dose of cholecalciferol, it has a stop-feed effect on the animal, which means that it will not continue to feed.

This is unlike when an animal takes a lethal dose of an SGAR and continues to eat more of the SGAR up until the point of death. The SGAR bioaccumulates in that animal's body and increases the likelihood of secondary poisoning to predators and carrion feeders.

AW: This also means there is a lower chance that rodents will overfeed and waste bait, which means the same efficacy will require fewer visits by professional applicators.

RF: There are two cholecalciferol formulations/products on the market, and they both have different label uses. One is the only rodenticide in the UK and Ireland that can be used in open areas and for burrow baiting.

The other has Apodemus sylvaticus (Field /Wood Mouse) on the label and cannot be used in open areas or for burrow baiting. Both cholecalciferol baits also have label approval and they both can be used for permanent baiting.

WHAT DID YOU LEARN?

An online CPD quiz based on this feature is now available. BPCA Registered members and affiliates can take a CPD quiz at any time.

bpca.org.uk/find-cpd or sign up at bpca.org.uk/affiliate