Assuring that 1080 toxicosis in the red fox (Vulpes vulpes) is humane. II. Analgesic drugs produce better welfare outcomes

Abstract

Fluoroacetic acid (1080) is a widely used vertebrate pesticide in Australia and New Zealand. In Australia it is used in meat baits as the primary method of control for the introduced red fox (Vulpes vulpes). Subsequent to the onset of initial signs, collapse and convulsions are associated with central nervous system disruptions where the animal is unresponsive to external stimuli, making an assessment of humaneness difficult. Prior to collapse and unconsciousness it would appear that there is potential for suffering to occur although its extent and nature during the entire toxicosis remains unclear. We investigated various formulations of 1080 with either analgesic or anxiolytic drugs in order to manage possible suffering experienced during 1080 poisoning of red foxes. Oral doses of 0.5 mg kg−1 1080 alone produced no visible signs for a mean of 205.3 min (±28 min, P < 0.05), but were lethal after signs that lasted a mean of 103 min (±16 min, P < 0.05). Combinations of 0.5 mg kg−1 1080 with either 10 mg kg−1 carprofen (CA), 0.4 mg kg−1 copper indomethacin (CI) or 10 mg kg−1 buspirone (BS) were assessed in pen trials and compared with a group that received 0.5 mg kg−1 1080 only and one that received the drug dose only. CI reduced the time between the onset of signs and death (P < 0.01) and CA reduced the overall intensity of activity from dosage to death (P < 0.05). A significant reduction in the incidence of retching during the onset of signs was observed in foxes that were coadministered CA (P < 0.05) or CI (P < 0.01) with 1080 compared with 1080 alone. The combination of BS and 1080 halved the mean activity from first signs to death, but was not statistically significant. In a separate trial, drug and 1080 combinations were delivered to penned foxes using an M-44 ejector. Neither 70 mg CA nor 2.8 mg CI appeared to affect the lethality of 1080 doses, although 70 mg BS produced a result that was equivocal and warrants further investigation. Coadministration of 70 mg diazepam was associated with the survival of six of nine foxes and suggests that there may be the potential for diazepam to act in the treatment of accidentally poisoned domestic dogs and this is discussed briefly. Given evidence for both central and peripheral analgesia, its potential to reduce the duration of signs and incidence of retching, CI shows immediate potential to be used with 1080 fox baits and to assist in delivering better welfare outcomes in fox control.