Acute oral toxicity of zinc phosphide: an assessment for wild house mice (Mus musculus)

Irregular plagues of house mice, Mus musculus, incur major economic impacts on agricultural production in Australia. The efficacy of zinc phosphide (ZnP), the only registered broadacre control agent for mice, is reported as increasingly variable. Have mice become less sensitive over time or are they taking a sub-lethal dose and developing aversion? In this laboratory study, the sensitivity of mice (wild caught; outbred laboratory strain) was assessed using oral gavage of a range of ZnP concentrations. The estimated LD₅₀ values (72–79 mg ZnP/kg body weight) were similar for each mouse group but are significantly higher than previously reported. The willingness of mice to consume ZnP-coated grains was determined. ZnP-coated grains (50 g ZnP/kg grain) presented in the absence of alternative food were consumed and 94% of wild mice died. Mice provided with alternative food and ZnP-coated wheat grains (either 25 or 50 g ZnP/kg grain) consumed toxic and non-toxic grains, and mortality was lower (33–55%). If a sublethal amount of ZnP-coated grain was consumed, aversion occurred, mostly when alternative food was present. The sensitivity of wild house mice to ZnP in Australia is significantly lower than previously assumed. Under laboratory conditions, ZnP-coated grains coated with a new higher dose (50 g ZnP/kg grain) were readily consumed. Consumption of toxic grain occurred when alternative food was available but was decreased. Our unambiguous findings for house mice indicate a re-assessment of the ZnP loading for baits used for control of many rodents around the world may be warranted.     

Conservation agriculture practices have changed habitat use by rodent pests: implications for management of feral house mice

Journal of Pest Science - The advent of ‘conservation agriculture’ (CA) farming using zero- or no-tillage practices and an accompanying change in crop rotations in the last...     

Effects of harvesting and stubble management on abundance of pest rodents (Mus musculus) in a conservation agriculture system

BACKGROUND

The shift to more environmentally sensitive agricultural practices over the last several decades has changed farmland landscapes worldwide. Changes including no-till and retaining high biomass mulch has been coincident with an increase in rodent pests in South Africa, India, South America and Europe, indicating a possible conflict between conservation agriculture (CA) and rodent pest management. Research on effects of various crop management practices associated with CA on pest rodent population dynamics is needed to anticipate and develop CA-relevant management strategies.

RESULTS

During the Australian 2020–2021 mouse plague, farmers used postharvest stubble management practices, including flattening and/or cutting, to reduce stubble cover in paddocks to lessen habitat suitability for pest house mice. We used this opportunity to assess the effects of both harvest and stubble management on the movement and abundance of mice in paddocks using mouse trapping and radio tracking. We found that most tracked mice remained resident in paddocks throughout harvest, and that mouse population abundance was generally unaffected by stubble management.

CONCLUSION

Recent conversions to CA practices have changed how pest house mice use cropped land. Management practices that reduce postharvest habitat complexity do not appear to reduce the attractiveness of paddocks to mice, and further research into new management strategies in addition to toxic bait use is required as part of an integrated pest management approach. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Measurement of equine laminar blood flow and vascular permeability by use of dynamic contrast-enhanced computed tomography

OBJECTIVE: To define the reference range for laminar blood flow (BF) and vascular permeability (VPM) in horses without laminitis by use of dynamic contrast-enhanced computed tomography (CT). ANIMALS: 9 adult horses that were not lame and had no abnormalities of the laminae or phalanges detectable via radiographic examination. PROCEDURES: Each horse was anesthetized by use of a routine protocol. Horses were placed in right or left lateral recumbency with the dependent forelimb in the CT gantry; only 1 limb of each horse was scanned. Serial 10-mm collimated transverse CT images were acquired at the same location every other second for 90 seconds during infusion of ionic, iodinated contrast medium. Custom software was used to estimate BF, VPM, and fractional vascular volume (FVV) in the dorsal, dorsomedial, and dorsolateral laminar regions. RESULTS: Among the 9 horses' forelimbs, mean +/- SD dorsal laminar BF was 0.43 +/- 0.21 mL*min(1)*mL(1). Mean dorsomedial and dorsolateral laminar BFs were 0.26 +/- 0.16 mL*min(1)*mL(1) and 0.24 +/- 0.16 mL*min(1)*mL(1), respectively. Mean dorsal laminar VPM was 0.09 +/- 0.03 mL*min(1)*mL(1). Mean dorsomedial and dorsolateral laminar VPMs were 0.16 +/- 0.06 mL*min(1)*mL(1) and 0.12 +/- 0.06 mL*min(1)*mL(1), respectively. Mean dorsal laminar FVV was 0.63 +/- 0.20 and dorsomedial and dorsolateral laminar FVV were 0.37 +/- 0.14 and 0.34 +/- 0.17, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: In horses, laminar BF, VPM, and FVV can be non-invasively measured by use of dynamic contrast-enhanced CT.     

Testing novel methods for assessing rule breaking in conservation

Many approaches to conserving and managing natural resources depend upon rules, but the existence of rules alone does not guarantee compliance. Information on rule breaking behaviour is needed for designing interventions to improve compliance. However, directly investigating rule breaking is difficult as perpetrators may not wish to identify themselves. Other disciplines have developed methods for answering sensitive questions but so far these have not been widely applied in conservation. Using rule breaking among fly fishers as a case study, we tested two methods specifically designed for collecting sensitive data (the randomised response technique (RRT) and the nominative technique), against a conventional self-complete questionnaire. RRT resulted in much higher estimates of the prevalence of rule breaking than the self-complete questionnaire, particularly for more sensitive questions. The nominative technique yielded extremely low estimates, possibly because respondents did not know enough about their friends’ rule breaking behaviour, or did not want to discuss it in a face-to-face interview. Despite requiring large sample sizes we suggest that RRT is a useful method for obtaining information about rule breaking and could be more widely used, for example in studies of poaching and illegal resource extraction.     

Bilateral uveal metastasis of a subcutaneous fibrosarcoma in a cat

A 6‐year‐old neutered male domestic short‐haired cat was presented to the Comparative Ophthalmology service at Michigan State University with a 3‐week history of decreased appetite and redness of the left eye. The left forelimb had been removed 15 months previously because of the presence of a subcutaneous fibrosarcoma. In the left globe, a large iridal mass was associated with increased intraocular pressure and retinal detachment. A smaller mass involving the right iris was also present. Imaging revealed a 2‐cm mass in the left caudodorsal lung lobe, and abdominal ultrasound showed multifocal bilateral renal masses. Aspirates of these masses were nondiagnostic. The left globe was removed for palliative reasons, and histopathology showed that fibrosarcoma was infiltrating the iris, choroid, and optic nerve. Despite systemic chemotherapy with doxorubicin, the animal died 4 months after initial presentation. Histopathology confirmed highly angioinvasive metastatic fibrosarcoma also in the right uveal tract, the lungs, and both kidneys.