Ethyl-iophenoxic acid as a quantitative bait marker for small mammals

Bait markers are indispensable for ecological research but in small mammals, most markers are invasive, expensive and do not enable quantitative analyses of consumption. Ethyl-iophenoxic acid (Et-IPA) is a non-toxic, quantitative bait marker, which has been used for studying bait uptake in several carnivores and ungulates. We developed a bait with Et-IPA, assessed its palatability to common voles (Microtus arvalis), and determined the dose-residue-relation for this important agricultural pest rodent species. Et-IPA concentrations of 40 to 1280 μg Et-IPA per g bait were applied to wheat using sunflower oil or polyethylene glycol 300 as potential carriers. In a laboratory study, common voles were offered the bait and blood samples were collected 1, 7, and 14 days after consumption. The samples were analyzed with LC-ESI-MS/MS for blood residues of Et-IPA. Sunflower-oil was the most suitable bait carrier. Et-IPA seemed to be palatable to common voles at all test concentrations. Dose-dependent residues could be detected in blood samples in a dose-dependent manner and up to 14 days after uptake enabling generation of a calibration curve of the dose-residue relationship. Et-IPA was present in common vole blood for at least 14 days, but there was dissipation by 33-37% depending on dose. Et-IPA meets many criteria for an "ideal" quantitative bait marker for use in future field studies on common voles and possibly other small mammal species.

Iophenoxic acid derivatives as markers of oral baits to wildlife. New tools for their detection in tissues of a game species and safety considerations for human exposure

The bait-marker iophenoxic acid (IPA) and its derivatives are increasingly used for evaluating and optimizing the cost-effectiveness of baiting campaigns on wildlife, particularly on game species such as the wild boar. We aimed to determine whether concentrations of the three main IPA derivatives ethyl, methyl and propyl-IPA measured on thoracic liquid extracts (TLE) of hunted wild boars may be representative of two exposure doses, 40 and 200 mg, from 20 to 217 days after ingestion. Then we developed a method of detection of the three IPA derivatives by LC/ESI-MS-MS in muscle and liver to evaluate the suitability of these two other tissues for monitoring the marked bait consumption and for measuring available residues in the meat of marked animals. Three semi-captive wild boars received 40 mg of each IPA derivative, three received 200 mg, and three, as controls, did not receive IPA. Blood serum was sampled 20, 197 or 217 days after IPA exposure according to animals and to the derivative. Wild boars were shot by gun after the different times of serum sampling times, and TLE, muscle and liver were sampled. Our results suggest that TLE is not a relevant tissue for quantitatively expressing IPA exposure. Due to interference, no analytical method was validated on TLE containing digestive material. On the other hand, quantifications in the muscle and particularly in the liver could discriminate wild boars that had ingested the two IPA doses from 20 days until 7 months after exposure, especially for the two long term markers ethyl and propyl-IPA. So IPA quantifications in the liver sampled on hunted animals appear to be a reliable tool for monitoring bait consumption in the field at a large scale. Nevertheless, whatever the ingested dose, ethyl- and propyl-IPA concentrations measured in the muscle and the liver of tested animals until 217 days after exposure, remained higher than 0.01 mg/kg, the Maximal Residue Limit (MRL) is recommended for molecules for which no toxicological data are available. Based on the range of IPA residues available in these two tissues, implications for humans consuming marked animals are discussed.

Analysis by LC/ESI-MS of iophenoxic acid derivatives and evaluation as markers of oral baits to deliver pharmaceuticals to wildlife

Iophenoxic acid and its derivatives (methyl, ethyl, and propyl) are organic chemicals used as markers in baiting campaigns to deliver vaccines, pharmaceuticals, contraceptives or poisons to wildlife. In this study we develop a method of detection of IPA derivatives by LC/ESI-MS (using butyl-IPA as internal standard) obtaining a limit of detection and quantification in wild boar (Sus scrofa) serum of 0.037 microg/ml and 0.123 microg/ml, respectively. The average recovery of IPA derivatives was 88% at levels >0.2 microg/ml, with coefficients of variation <15%. Wild boars in captivity were orally treated with 5 mg/kg b.w. (three adults) or 15 mg/kg b.w (two piglets and three adults) of methyl-, ethyl- and propyl-IPA and the serum levels of these were monitored during 18 months after dosing. Ethyl- and propyl-IPA were detected up to 18 months after a single oral dose in wild boar, especially at 15 mg/kg. Methyl-IPA was detected until 9 months after dosing. Half-lives of methyl-, ethyl- and propyl-IPA were (mean+/-SD) 41+/-5, 183+/-85 and 165+/-45 days, respectively. One control piglet not exposed to IPA, but housed in the same facility than treated animals showed detectable IPA levels in serum. Piglets born from mothers exposed to marked baits also showed detectable IPA levels in serum. The high persistence of Et- and Pr-IPA must be considered in the field trials, because the presence of the product at low levels in one animal may not reflect a real ingestion of the marked bait.

DNA genotypes reveal red fox (Vulpes vulpes) abundance, response to lethal control and limitations of contemporary survey techniques

Context. Scat genotyping has not been routinely used to measure fox (Vulpes vulpes) abundance and our study sought to provide a benchmark for further technique development and assessment of field methods. Aims. This study sought to provide a comparative assessment of some common methods used to determine fox density and contrast their success with scat DNA genotyping. Methods. DNA recovered from fox scats was used to genotype individual red foxes and determine their abundance at four transects. Population indices were also developed from bait take, scat counts and sand plot tracks using index-manipulation-index (IMI) procedures on the same transects. Known samples of foxes were taken from two treatment transects using cyanide delivered in the M-44 ejector to manipulate the population and to recover foxes at the end of the trial. Key results. Replicated counts on a 41-km-spotlight transect at the field site before and after the population manipulation had low variance and good correlation (r2 = 0.79, P < 0.01). Scat genotypes revealed 54 foxes in eight days and, when combined with biopsy DNA from recovered foxes, a minimum known to be alive (KTBA) density of between 1.6 and 5 foxes km–1 was calculated for the transects. Overall, 15/30 (50%) of all recovered foxes had not been detected by scat genotyping, 23/53 (49%) of KTBA genotypes were detected only once and 5/54 (9.5%) of foxes were found to have moved between two transects. Conclusions. At transects where population manipulation occurred, surviving individuals contributed significantly more scats than at the control transects and some individuals were detected at bait stations at a much greater frequency. This strongly suggested that they had contributed disproportionately to some IMI density estimates that were probably influenced by a change in the activity of some individuals rather than changes in population density alone. At one transect, eight foxes were confirmed to be present by spotlight surveys and were detected by scat and KTBA genotypes, yet were undetected by scat, bait station and sand plot indices. Implications. Scat and other DNA-based survey techniques provide a great deal of information about the identification and movement of individuals and if DNA sampling methods can be made more efficient they have the potential to provide accurate abundance estimates that are independent of the control technique.

Vaccination of feral pigs (Sus scrofa) using iophenoxic acid as a simulated vaccine

OBJECTIVES

To develop an encapsulation method for delivery of vaccines to feral pigs, and quantify the effect of iophenoxic acid on captive feral pig blood iodine concentrations to assist in investigation of factors affecting vaccine uptake.

DESIGN AND METHODS

Feral pigs were administered iophenoxic acid by oral gavage, and consumption was assessed for different encapsulation methods in baits. Blood iodine concentrations were monitored for eight days after consumption. The relationship between dose rate, time since dosing and blood iodine concentration was assessed for gavaged and baited captive feral pigs. Wild feral pigs were baited with PIGOUT baits containing 20 mg of encapsulated iophenoxic acid to simulate a vaccination program. Using knowledge from the pen studies, bait uptake and factors affecting bait uptake were investigated.

RESULTS

Bait-delivered iophenoxic acid led to variable and inconsistent changes in blood iodine concentrations, in contrast to pigs receiving iophenoxic acid by gavage. This precluded accurate assessment of the quantity consumed, but still allowed a conservative determination of bait uptake. Iophenoxic acid in smaller capsules was consumed readily. Increasing baiting intensity appeared to increase bait uptake by wild feral pigs, and pigs of varying sexes, ages and weights appeared equally likely to consume baits.

CONCLUSIONS

Encapsulated liquids can be delivered to feral pigs within baits, should the need to vaccinate feral pigs for fertility or disease management arise. High baiting intensities may be required.

Liquid chromatography–electrospray ionization mass spectrometry for direct identification and quantification of iophenoxic acid in serum

A liquid chromatographic-electrospray ionization mass spectrometric technique was developed for direct quantitation of iophenoxic acid (IA) in serum. IA was spiked into canine, feline, bovine, equine, and porcine sera, extracted, and quantified using negative ion monitoring following chromatographic separation on a Luna C18(2) 3 microm (100 mm x 2.1mm) reversed-phase column. The limit of detection was 25 ng/mL and the limit of quantification was 50 ng/mL. Inter- and intra-assay accuracy (86-113% and 87-115%, respectively) and precision (1.8-7.7%) were calculated. Analysis of serum collected from feral pigs, raccoons, and opossums following ingestion of IA-marked baits confirmed the appropriateness of this method for bait acceptance studies.

Control of pest mammals for biodiversity protection in Australia. I. Patterns of control and monitoring

Foxes, wild dogs, feral cats, rabbits, feral pigs and feral goats are believed to have deleterious impacts on native biodiversity in Australia. However, although considerable resources have been expended controlling these six species, little is known about national patterns and costs of control and monitoring. We therefore conducted a survey of pest-control operations undertaken by conservation-focused organisations in Australia. A total of 1306 control operations were reported, with most conducted during 1998–2003: there was little information prior to 1990. Foxes and rabbits were the most, and feral cats the least, frequently controlled pest species. The total area on which control was undertaken in 2003, the year for which most information was available, ranged from ~0.4 × 104 km2 for feral cats to ~10.7 × 104 km2 for foxes. A wide range of techniques and intensities were used to control each of the six species. The estimated cost of labour expended on control in 2003 ranged from $0.4 × 106 for feral cats to $5.3 × 106 for foxes. Monitoring of the pest or biodiversity occurred in 50–56% of control actions in which foxes, wild dogs and feral cats were targeted, but only 22–26% of control actions in which rabbits, feral pigs and feral goats were targeted. Our results are discussed in relation to previous studies of pest animal control and monitoring in Australia.

Evaluation of the tranquilliser trap device (TTD) for improving the humaneness of dingo trapping

Predation of sheep and cattle by the dingo (Canis lupus dingo) is implicated in significant stock losses throughout much of mainland Australia. Leg-hold traps are commonly used for dingo control and ways are sought to improve the humaneness of these devices. We evaluated the performance of the tranquilliser trap device (TTD) attached to Victor Soft-Catch® traps for their ability to deliver a sedative and anxiolytic drug to trapped dingoes. A trapping programme was conducted in south-west Queensland where traps were set alternatively with a TTD containing either 800 mg of diazepam (drug TTD) or a placebo (placebo TTD). All TTDs included 20 mg of the bait marker iophenoxic acid (IPA) to ascertain dosing success. Each trap was fitted with an activity-monitoring data logger that recorded time of capture and subsequent dingo activity. In 41 out of 48 (85.4%) captures the TTD was ruptured and released its contents. No elevation in serum iodine levels above I mg ml-1 resulting from the ingestion of IPA occurred in 8 out of 36 (22.2%) captures, which suggests a higher rate of dosage failure. Dingo activity was highest in both groups immediately after capture, but declined after the first hour in each. The activity of dingoes that accepted a drug TTD was significantly reduced compared to those that took the placebo. However, tooth and limb damage scores did not differ significantly between the drug and placebo group. Much of the physical trauma may have occurred within the first hour of capture when activity was intense and before drug onset in the TTD drug group. The use of TTDs containing sedative and anxiolytic drugs has the potential to reduce anxiety and distress associated with prolonged captivity, but the delivery of a lethal agent that is rapidly acting and humane may result in better welfare outcomes.

High-performance liquid chromatographic determination of iophenoxic acid in serum

Iophenoxic acid (IPA), a marker used to investigate the feeding behaviour of bait-consuming animals has previously been indirectly determined by measuring protein-bound iodine levels in serum or plasma. For the first time a method is reported for the direct determination of IPA in biological fluids. IPA was determined in de-proteinized serum by high-performance liquid chromatography (HPLC) on a C18 column with a mobile phase of acetonitrile-water. Isocratic and gradient systems are described with limits of detection of 0.2 microgram/ml (isocratic) and 0.05 microgram/ml (gradient). Recoveries from fox serum were 85% at 0.5 microgram/ml, 95% at 5 micrograms/ml and 91% at 50 micrograms/ml.