Sensitivity of High Conservation Value Birds to Para-Aminopropiophenone (PAPP) Determined by Sub-Lethal Dose–Response Assay

Abstract

Para-aminopropiophenone (PAPP) is a methaemoglobin (MetHb) forming compound used for the lethal control of invasive carnivores and mustelids. By measuring the dose-dependent inhibition of O2 transport arising from the oxidation of haemoglobin (HbFe2+) to MetHb (HbFe3+), we determined the sensitivity of nine bird species to PAPP. A methaemoglobinaemia absorbance index (MAI) was validated in five common bird species to determine thresholds associated with a 99% probability of survival (ST99) and a 50% probability of mortality (LT50). Dose–response trials in high conservation value birds sought MAI values below the ST99 threshold, projecting the LT50 value and avoiding the need for lethal outcomes. Black-backed gull (LT50 = 1784.7) and eastern rosella (LT50 = 1074 mg kg−1) were the most tolerant species, while brown kiwi (LT50 = 8.4 mg kg−1) and weka (LT50 = 9.3 mg kg−1) were the most sensitive. Takahē were of intermediate acute sensitivity (LT50 = 51 mg kg−1), although protracted impacts on haemoglobin were observed in takahē up to 72 h later and associated with PAPP doses as low as 25.6 mg kg−1. In pukeko (LT50 = 138.4 mg kg−1), protracted declines in haemoglobin 72 h later occurred at doses as low as 29.5 mg kg−1, while at higher doses (253 and 112 mg kg−1), deaths resulted after 4–6 days. Based upon PAPP doses that caused acute and protracted responses, we provide estimates for the lowest observable adverse effect level (LOAEL) and no observable effects level (NOEL) for nine bird species.

Non-Lethal Dose-Response Models Replace Lethal Bioassays for Predicting the Hazard of Para-Aminopropiophenone to Australian Wildlife

“…An experimental endpoint (85% MetHb) had been validated after preliminary trials in red foxes [28] and feral cats (Marks, unpublished data) [32], where the Animal Ethics Committee had permitted death as an endpoint in order to validate the utility of non-lethal endpoints using MetHb thresholds. Published fox data for PAPP + DMSO (Marks et al 2004) were re-analysed in this paper alongside new data developed for PAPP + PEG formulations.…”

Monitoring methaemoglobinaemia in birds using 5 μL of whole blood

“…As an alternative to bioassays that use dichotomous lethal-dose data (survival or death) to establish the hazard of MetHbforming agents, we sought continuous data to directly measure the dose-dependent impacts caused by MetHb-forming agents. This approach was selected to reduce animal use and to permit dose-response modeling that avoids the need to use death as an experimental endpoint in high conservation value bird species [17].…”

“…Consultation with wildlife veterinarians sought to identify ways to accommodate unique behavioral features encountered in new species so to reduce unique causes of stress. Details of the specific anaesthesia, handling procedures and dose-response data are presented elsewhere [17] and are only briefly restated here. A stock solution of 375 mg mL -1 PAPP dissolved in dimethyl sulfoxide (DMSO) was prepared by heating the solution to between 38-41˚C with sonication.…”

“…In highly tolerant birds, doses were increased by more than a factor of x 1.5 until perturbations in absorbance values were detected, enabling a series of doses to be selected to produce more intense clinical signs of methaemoglobinaemia. The overall range of PAPP doses used varied between 0.6-855 mg kg -1 and the full range of doses used in each species are reported elsewhere [17]. All birds were lightly anaesthetised to allow baseline blood samples to be taken at T0, other than for kiwi and weka where no anaesthesia was recommended by attending veterinarians.…”

“…Methaemoglobinaemia, is a functional anaemia where MetHb displaces HbO, in a relationship that is strongly inversely correlated [10,28]. Individually, neither MetHb or HbO concentrations proved to be as successful at predicting bird survival as the MAI [17]. In small blood samples, relative changes in absorbance between 575 nm and 630 nm appeared far less affected by error than those referenced to zero baselines that might shift slightly between samples due to imperfections in the cuvette repositioning or changes in the optical characteristics of the sample itself.…”