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Biological rodent control

Cats are historical predators of small rodents, particularly mice. When introduced on-farm, they instinctively stalk, hunt and kill a small number of rodents. The on-farm presence of cats can influence rodent behaviour, with the higher predation risk making them less likely to move from shelter (Themb’alilahlwa et al., 2017). Cats can also prey on birds, with young chicks particularly vulnerable, so they should be denied access to areas where birds are contained. This has the flow-on effect of making sheds and poultry houses safe spaces for rodents, potentially increasing rodent populations in internal production areas, and raising disease and contamination risk. Cats also serve as intermediate hosts for the intracellular parasite Toxoplasma gondii, which is shed in cat faeces. It can infect all warm-blooded animals, posing a risk to the health of chickens and humans (Meerberg et al., 2014).

The use of anticoagulant rodenticides, which persist in the liver tissue of baited rodents, can lead to the secondary poisoning of cats that predate them (Gillies and Pierce, 1999). Therefore, using cats to supplement chemical control strategies is not viable. Cats can suppress rodent activity, but are unlikely to significantly reduce on-farm rodent numbers (Mahlaba et al., 2017; Brown and Henry, 2018). Because cats also pose a potential hazard to bird and human health, they are not recommended as a suitable rodent control method in poultry operations.

Domestic dogs are commonly used on farms and homes around the world to control rodents, although there is a lack of practical scientific evidence about their level of impact on rodent activity and abundance. Similar to cats, dogs may hunt and kill small numbers of rodents, but because rodents reproduce rapidly, dogs are unlikely to significantly reduce rodent populations on-farm. The presence of dogs on-farm has been observed to create a heightened fear for foraging rodents (Themb’alilahlwa et al., 2017). As a result, rodents become less likely to move from shelter or cover, and overall rodent activity is reduced.

Domestic dogs can serve as well-rounded biological control agents, suppressing rodent activity and acting as deterrents for foxes and wild dogs that pose a threat to livestock. However, as with all biological rodent control agents, the use of chemical rodenticides, either anticoagulants or acute poisons, exposes them to secondary poisoning. While dogs will not typically feed on rodents, they are susceptible to anticoagulant rodenticides. Numerous examples of anticoagulant toxicoses from the inadvertent consumption of bait are published in veterinary literature (Sheafor and Couto, 1999; Valchev et al., 2008; Waddell et al., 2013; DeClementi and Sobczak, 2018). The use of dogs to supplement existing chemical rodent control strategies is potentially hazardous. Poultry producers who use rodenticide baits alongside domestic dogs must ensure that bait is securely housed in lockable, tamper-proof bait stations.

Rodents are a natural part of the diet of Australian native birds, including the barn owl (Tyto alba), Australian boobook (Ninox boobook) and laughing kookaburra (Dacelo novaeguineae). Therefore, native prey bird species are potential candidates for biological rodent control on poultry farms. In many parts of the world, barn owls are used to control rodents (Charter et al., 2010; Meyrom et al., 2009; Motro et al., 2010; Taylor, 1994). They feed on all rodent species found on poultry farms and can be attracted or introduced to specific sites by providing hollow nesting boxes (Newton, 1998). Unfortunately, most other native bird species have natural habitats that can span hundreds of hectares, therefore there are practical limitations in attracting and containing them within the areas near poultry operations.

Using native bird species alongside chemical rodent control may lead to secondary poisoning. Scientific evidence implicates current wide use of anticoagulant rodenticides as the source of some wildlife poisoning (Mendenhall and Pank, 1980; Martin et al., 1994; Thomas et al., 2011; Murray, 2018). Wild bird species are also potentially implicated with the spread of poultry diseases, including Newcastle disease virus and avian influenza (Ip et al., 2015; Brown and Bevins, 2017). The use of native predatory birds to control rodents on Australian poultry operations is novel, but due to the potential environmental and biosecurity implications, it is not recommended.

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